Author Topic: Opamps - Die pictures  (Read 6887 times)

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Offline Noopy

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Opamps - Die pictures
« on: June 10, 2020, 07:42:33 pm »

Hi all,

if you are interested in more opamp die pictures I can post them here.


Till know I have taken pictures of a


Raytheon LM318

https://www.richis-lab.de/Opamp05.htm

Thomson LM318

https://www.richis-lab.de/Opamp06.htm

Sescosem SFC2741

https://www.richis-lab.de/Opamp07.htm

Signetics NE5534

https://www.richis-lab.de/Opamp01.htm

 :popcorn:
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #1 on: June 10, 2020, 08:25:26 pm »
Coincidence: LM318 actually has a somewhat similar three stage topology to NE5534, although it may be hard to see it in this jungle of a schematic.
Capacitors are also connected in the same way, only one is not used (or perhaps not included in the datasheet). National's "Linear Brief" LB-17 explains a few things about this design.

Did you have some particular interest in this chip or just opened it because somebody from the forum sent you one?

Many precision amps like OP-07 or LT1028 (LT1115 is at Zeptobars) also use similar three stage topologies with similar compensation. LM118/318 was the first as far as I know.

BTW, those "adjustable" resistors appear to be simply pinch resistors. This has nothing to do with adjustments or precision of any kind, their tolerance is quite poor actually, but everything to do with producing high resistance on minimum die area.
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #2 on: June 10, 2020, 08:34:49 pm »
Coincidence: LM318 actually has a somewhat similar three stage topology to NE5534, although it may be hard to see it in this jungle of a schematic.
Capacitors are also connected in the same way, only one is not used (or perhaps not included in the datasheet). National's "Linear Brief" LB-17 explains a few things about this design.

Interesting!  :-+


Did you have some particular interest in this chip or just opened it because somebody from the forum sent you one?

The opamps just appeared in my inbox.  ;D


BTW, those "adjustable" resistors appear to be simply pinch resistors. This has nothing to do with adjustments or precision of any kind, their tolerance is quite poor actually, but everything to do with producing high resistance on minimum die area.

I agree with you principally.
I speculated whether Raytheon changed the length of the overlay to adjust the resistors. Indeed not very accurate...

Offline Noopy

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Re: Opamps - Die pictures
« Reply #3 on: June 11, 2020, 06:31:59 am »
Two more words about the suspected adjustable resistors.
Since they are pinch resistors they are commonly not very accurate. Anyway one can speculate whether Raytheon had a possibility to tune them (by mask modification perhaps).
It seems not plausible that Raytheon puts the least accurate resistors in places where they originally wanted the most accurate.

Offline David Hess

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Re: Opamps - Die pictures
« Reply #4 on: June 11, 2020, 11:55:49 am »
Coincidence: LM318 actually has a somewhat similar three stage topology to NE5534, although it may be hard to see it in this jungle of a schematic.

...

Many precision amps like OP-07 or LT1028 (LT1115 is at Zeptobars) also use similar three stage topologies with similar compensation. LM118/318 was the first as far as I know.

Unlike those, the 318 uses emitter degeneration to lower transconductance of the first stage allowing better frequency response but this increases noise and drift making it unsuitable for audio and precision applications.  I think it was the first commercial integrated operational amplifier suitable for video applications.
 

Offline magic

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Re: Opamps - Die pictures
« Reply #5 on: June 11, 2020, 06:27:14 pm »
Two more words about the suspected adjustable resistors.
Since they are pinch resistors they are commonly not very accurate. Anyway one can speculate whether Raytheon had a possibility to tune them (by mask modification perhaps).
It seems not plausible that Raytheon puts the least accurate resistors in places where they originally wanted the most accurate.
Yes, I think you're right about the tuning thing. These resistors set things like input/output stage bias currents, etc. Apparently some production variation didn't bother them too much.

I thought they simply used this slashed resistor symbol to indicate pinch resistors for whatever reason, but that's clearly not the case. There are pinch resistors drawn normally on the schematic and there is a resistor drawn with a slash which is not a pinch resistor (R2).

BTW, this is not Raytheon's schematic. Get the original from National, it has component numbers and typical values :-+
Raytheon also cheated in the bias circuit and R2 doesn't even exist in their version, but it exists on the Thomson.

Unlike those, the 318 uses emitter degeneration to lower transconductance of the first stage allowing better frequency response but this increases noise and drift making it unsuitable for audio and precision applications.
So does Douglas Self, though not as much.
Noise seems about on par with RC4558 which often successfully passes as NE5532 on AliBay :) 10~15nV/rtHz isn't terribly bad for line level signals.

On the upside, open loop linearity is improved. There is even an LM318 thread on DIYAudio: somebody swore that it's good for driving an external power stage, but its own DC linearity driving a few kΩ load was reported as "between that of µA709 and µA741".
https://www.diyaudio.com/forums/solid-state/349054-lm318-distortion.html
« Last Edit: June 11, 2020, 07:33:13 pm by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #6 on: June 12, 2020, 06:27:45 am »
BTW, this is not Raytheon's schematic. Get the original from National, it has component numbers and typical values :-+
Raytheon also cheated in the bias circuit and R2 doesn't even exist in their version, but it exists on the Thomson.

You are right but since Raytheon printed this schematic in their datasheet I wanted to refer to this one.
 
Perhaps they had to change one small thing in their design to make it "legal" and selected R2.  :-/O

Offline magic

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Re: Opamps - Die pictures
« Reply #7 on: June 12, 2020, 07:41:44 am »
The whole bias generator is missing. Look near IN+ - it's a simple 1:3 current mirror fed by that long, snaking resistor. At the beginning of the resistor there might be an emitter follower. In other Raytheon circuits the base would be connected to an n-JFET + zener reference, though I can only identify a JFET here. Not sure what's going on, but it certainly is not the real LM318 bias circuit.

Ditto with RC5534. There is a metal layer diagram in the datasheet and it has a black hole where the bias generator ought to be (left of the output transistors). Proper NE5534 bias generator contains a pair of lateral PNPs. Nothing like that is seen anywhere besides the second stage differential pair.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #8 on: June 12, 2020, 08:37:31 am »
You are right. The bias circuit is very different, less complex:



 :-+

Offline David Hess

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Re: Opamps - Die pictures
« Reply #9 on: June 12, 2020, 09:38:38 pm »
Unlike those, the 318 uses emitter degeneration to lower transconductance of the first stage allowing better frequency response but this increases noise and drift making it unsuitable for audio and precision applications.

So does Douglas Self, though not as much.

I should have said low noise audio like microphone amplifiers.  After the first gain stage, the added noise is irrelevant unless it limits dynamic range.

Quote
Noise seems about on par with RC4558 which often successfully passes as NE5532 on AliBay :) 10~15nV/rtHz isn't terribly bad for line level signals.

The datasheets I have show twice the broadband noise and 6 times the low frequency noise of the RC4558.

Quote
On the upside, open loop linearity is improved. There is even an LM318 thread on DIYAudio: somebody swore that it's good for driving an external power stage, but its own DC linearity driving a few kΩ load was reported as "between that of µA709 and µA741".
https://www.diyaudio.com/forums/solid-state/349054-lm318-distortion.html

The 318 has about twice the output current capability as common lower power parts and its high speed allows it to operate inside of a feedback loop.  In the past I have used it as a driver for these reasons.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #10 on: June 27, 2020, 08:14:52 pm »
Hi all!

Today I can show you an opamp configured to act as voltage follower:

https://richis-lab.de/Opamp08.htm

LM310 built by Silicon General






Schematic is taken from National Semiconductor datasheet.
It´s a differential amplifier (red) with an output stage (purple). No VAS since a voltage follower needs no voltage amplification. And with lower amplification you need less negative feedback. With less negative feedback a bigger bandwith is still stable.  :-+




The die is not extremly interesting...

 :popcorn:
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #11 on: June 27, 2020, 09:12:56 pm »
Well, one interesting thing is that the circuit uses a bunch of superbeta NPNs and it looks like there is no obvious way to tell them apart visually.

And class A output stage. Probably that's the true reason why it's so fast: no dirty PNPs in the signal path ;)
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #12 on: June 28, 2020, 05:36:17 am »
You are right. There should be superbeta NPNs but as far as i know you can´t really distinguish them from "normal" NPNs. The base is just thinner…

There is a application note advertising the speed of the LM310 and explaining it with the use u NPNs.  :-+

Offline magic

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Re: Opamps - Die pictures
« Reply #13 on: June 28, 2020, 06:28:24 am »
It's a common thing in "high speed" amplifiers built on 1970's noncomplementary processes. The 318/5534 also bypass their PNP differential stage with capacitors to yield an amplifier which is 100% NPN at high frequencies.

There is one textbook author who will want you to believe that all of these capacitors are for nested Miller feedback, ignore him and read LB-17 ;)
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #14 on: June 28, 2020, 10:08:08 am »
Yes, the right mixture of negative feedback and feedforward. That's the trick.
What's LB-17?

Offline magic

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Re: Opamps - Die pictures
« Reply #15 on: June 28, 2020, 10:49:57 am »
The NatSemi paper about LM118/318 which I mentioned before.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #16 on: June 28, 2020, 12:05:15 pm »
Of course! Sorry, I was confused somehow.  :-+

Offline SeanB

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Re: Opamps - Die pictures
« Reply #17 on: June 28, 2020, 12:55:45 pm »
Now I know how those hundreds of SFC2741 op amps I changed over the years look like inside, thank you. most were changed because of offset drift going outside the limits that could be compensated, which was not bed after 20 years of being alternately baked and chilled.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #18 on: June 28, 2020, 01:11:05 pm »
More coming soon!  :) :popcorn:

Offline David Hess

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Re: Opamps - Die pictures
« Reply #19 on: June 28, 2020, 04:23:22 pm »
Check out Linear Technology application note 16 where Widlar himself describes some details of PNPs on an NPN only process in these types of integrated circuits.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #20 on: July 07, 2020, 08:49:17 pm »
Today I have a comparator, a LM306, for you:








https://www.richis-lab.de/Opamp09.htm


It´s a comparator, not a normal opamp. Note the difference.  :-/O :)

Offline Hydron

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Re: Opamps - Die pictures
« Reply #21 on: July 08, 2020, 09:53:33 pm »
Love the pictures!

Have you looked at any of the more exotic modern analogue parts? Or are they normally covered with lots of metal etc, obscuring the interesting bits? I'm thinking of stuff a bit out of the ordinary like a AD8129/8130 (I assume there will be trimmed parts etc involved in one of those).
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #22 on: July 09, 2020, 03:22:27 am »
That´s nice to hear!  :-+

Right at the moment I just decap the parts people have donated. Often these parts are from the older generation but basically I decap everything.
Especially in the opamp category I mostly have older parts. But I put the AD8129 on my to-do-list. Sounds interesting! :-+

Offline magic

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Re: Opamps - Die pictures
« Reply #23 on: July 09, 2020, 06:55:44 am »
Have you looked at any of the more exotic modern analogue parts? Or are they normally covered with lots of metal etc, obscuring the interesting bits? I'm thinking of stuff a bit out of the ordinary like a AD8129/8130 (I assume there will be trimmed parts etc involved in one of those).
Perhaps not covered by lots of metal, but newer parts may use more than one metal layer which gives a bit of extra headache. You can see what it looks like on Noopy's AD587 voltage reference photos; thankfully that one had only two layers.

The amplifiers you listed certainly use a true complementary process which means NPN and PNP will be much more similar to each other.

Zeptobars probably has photographs of some more advanced analog parts.
 

Offline macboy

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Re: Opamps - Die pictures
« Reply #24 on: July 09, 2020, 01:11:33 pm »
Unlike those, the 318 uses emitter degeneration to lower transconductance of the first stage allowing better frequency response but this increases noise and drift making it unsuitable for audio and precision applications.
So does Douglas Self, though not as much.
Noise seems about on par with RC4558 which often successfully passes as NE5532 on AliBay :) 10~15nV/rtHz isn't terribly bad for line level signals.

On the upside, open loop linearity is improved. There is even an LM318 thread on DIYAudio: somebody swore that it's good for driving an external power stage, but its own DC linearity driving a few kΩ load was reported as "between that of µA709 and µA741".
https://www.diyaudio.com/forums/solid-state/349054-lm318-distortion.html

I have an old instrument, "Precision Filters 602 Dual Anti-Alias Filter", which uses LM318H and LM301 in TO-99 cans for the analog circuitry. Measured with 80 kHz bandwidth, I measure around 3 ppm (0.0003%) THD+N. The THD only (20 harmonics) measures at 0.8 ppm (0.00008%) which is equivalent to the measurement floor of my VP-7722, so it is perhaps much less, but not higher than that. The instrument dates back to ca. 1970's.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #25 on: July 10, 2020, 09:54:41 pm »
Today I have an old LM360 for you:





With the same die you can build a LM361.  :-+

https://www.richis-lab.de/Opamp10.htm

 :popcorn:

Offline Noopy

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Re: Opamps - Die pictures
« Reply #26 on: July 25, 2020, 07:28:36 pm »
Today I have a fake NE5534 for you:

https://www.richis-lab.de/Opamp11.htm

1,40€ for ten of these bugs including shipping.  :palm:




Tried to fake a Texas Instruments Logo? I don´t know.  :-// :-DD




The number 659 doesn´t really fit. It seems to be a RC4558.  :--

 :popcorn:

Offline magic

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Re: Opamps - Die pictures
« Reply #27 on: July 25, 2020, 08:04:41 pm »
You were lucky ;D
I got LM358 and so did some Turkish poster here the other day.

If you are looking for recycled authentic NE5532/4 from China it may be hard. I tend to look for auctions with positive feedback and preferably including buyer's photos of the delivered ICs. Prefer auctions which show unblurred manufacturer logo. But it's still lottery - I once ordered from an auction with a real photograph of ON Semi NE5534 and got a mix of recycled chips from unknown manufacturers with fake NXP branding (NXP never made those chips). At least they weren't completely fake.

edit
Wait, why all the pads look like they had been bonded?
Did they connect the second channel's bonding pads to the compensation/balance pins?
Or is it actually a normally bonded dual opamp, not pin-compatible with single opamps and there will be smoke if somebody tries to use it?
« Last Edit: July 25, 2020, 08:09:31 pm by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #28 on: July 25, 2020, 08:42:58 pm »
I searched for the cheapest NE5534 to find a fake. :D

I assume it's a RC4558 with the pinout of a RC4558. Probably they recycled RC4558 and changed them to NE5534 to make more money.
Normal (NE5534) connection will probably give you magic smoke...

Offline magic

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Re: Opamps - Die pictures
« Reply #29 on: July 25, 2020, 08:57:48 pm »
The shape of the packages looks Chinese and I found this exact die in a few different fake opamps. It's smaller than Raytheon or TI dice. It's some Chinese clone of RC4558 with fake markings.

Smarter fakers modify the pinout to be compatible with single opamps.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #30 on: July 25, 2020, 09:07:57 pm »
The shape of the packages looks Chinese and I found this exact die in a few different fake opamps. It's smaller than Raytheon or TI dice. It's some Chinese clone of RC4558 with fake markings.

That would explain why there are the numbers 659 which don't match with a RC4558.

Offline magic

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Re: Opamps - Die pictures
« Reply #31 on: July 25, 2020, 10:04:35 pm »
Some Chinese opamps:
https://www.eevblog.com/forum/beginners/opamp-input-offsets-working-in-the-opposite-direction-to-what-i-expect/25/
https://www.eevblog.com/forum/projects/whats-inside-the-cheapest-and-fakest-jellybean-opamps/
Have you really not seen those threads yet?

Yes, they sometimes incude some numbers and logos, nobody knows what they mean.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #32 on: July 25, 2020, 10:20:09 pm »
Of course I have seen those threads!  ;D
But that was some time ago and I have forgotten you already had found the numbers 659.

Nevertheless I´m not sure whether these 659-dies are conterfeits.
I know the datasheet describes the RC4558 to be bigger but zeptobars already found one smaller than that (bigger than this one here). Perhaps they did another die shrink and the opamp found here is no fake-RC4558 but a real one?

Offline Noopy

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Re: Opamps - Die pictures
« Reply #33 on: August 03, 2020, 03:18:07 pm »
I have something for you AMD built just before they started up their 7nm-fabrication.  ;D







https://www.richis-lab.de/Opamp12.htm


Looks quite similar to the Silicon General LM310 (https://www.richis-lab.de/Opamp08.htm) but has some differences.  :-/O



Offline David Hess

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Re: Opamps - Die pictures
« Reply #34 on: August 03, 2020, 09:19:15 pm »
I have something for you AMD built just before they started up their 7nm-fabrication.  ;D

Few people remember that AMD second sourced linear ICs.  I remember having to remove them as a supplier because too many parts had popcorn noise which is a processing problem.  I heard cussing over the reliability of their UVEPROMs also.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #35 on: August 17, 2020, 06:47:27 pm »
I took pictures of a OPA676 (thanks to dzseki).
That´s a very interesting opamp! It can go up to 185MHz with a slewrate of 350V/µs and it has two differential inputs which you can switch as you want.
Even more interesting: The OPA676 is integrated on an universal die. Something like an analog gatearray.






The two metal layers are designed by Burr-Brown. The "analog gatearray" is supplied by VTC:






More pictures here:

https://www.richis-lab.de/Opamp13.htm

 :popcorn:
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #36 on: August 20, 2020, 04:01:20 am »


Today I have a LF355 for you. This one was manufactured 1977.  :-+




Although the LF355 is the slowest opamp of the LFx5x-family, the capacitors are not as big as possible. I assume 1977 TI wasn´t sure how big they needed the capacitors to get stable operation and because of that they made the possible capacitor area bigger...  :-/O


https://www.richis-lab.de/Opamp14.htm


 :popcorn:
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #37 on: August 20, 2020, 07:20:32 am »
Damn, thank you, man. I now know what was inside my fake AD797 from AliExpress :-DD

I couldn't figure out how those input transistors work. JFET :palm:

But wait, is this a genuine LF355?
« Last Edit: August 20, 2020, 07:41:33 am by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #38 on: August 20, 2020, 07:48:00 am »
At least it was an opamp! :D

Offline magic

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Re: Opamps - Die pictures
« Reply #39 on: August 20, 2020, 09:07:36 am »
Did you get this chip from eBay?

There is no LF-anything in the 1984 Texas Instruments linear databook. There is a lot of second source LM parts, second sources of half a dozen other manufacturers, and there are TI's own TL07x JFET opamps and many other TL and TLC devices, but I can't see a single National JFET chip of any sort.

Their current datasheet SNOSBH0D dates to year 2000, FWIW.
« Last Edit: August 20, 2020, 09:09:14 am by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #40 on: August 20, 2020, 09:44:44 am »
Hm, you are right, that´s strange...

I got it from Ebay and the printing is very modern and clean. That is somehow suspicious with such an old part.

But it seemed plausible. I have three different National Semiconductor LF355 here. All three have the same design with two different revisions. They look quite similar to the "TI LF355" but are not the same. It seemed quite plausible that both companys had built one.

 :-//

Offline magic

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Re: Opamps - Die pictures
« Reply #41 on: August 20, 2020, 10:26:19 am »
Actually my chip is slightly different but I'm pretty sure it's the same LF15x circuit. Maybe one of the faster versions because the capacitors are smaller.

And there are two capacitors, I think the one near pin 4 is the compensation capacitor indicated on the schematic and the one near pin 1 is something else. One plate is connected to ground.

The large JFETs on the left appear to be the input devices, pins 1 and 5 go to another pair of structures which probably are JEFTs and I have no idea what are the transistors in the middle. Perhaps JFET constant current sinks?

I'm not sure why the connections to input JFET gates are swapped. On my chip, the IN+ JFET is near the IN+ pad and the IN- JFET is near the IN- pad.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #42 on: August 21, 2020, 11:48:19 am »
The second capacitor is connected to the non-inverting output of the differential stage. There is a more detailed schematic in a National datasheet showing this capacitor.


I now have pictures of the other LF355 (National Semiconductor). First one was built 1982:










The second one was built 1988:






That´s odd:



The 1982-LF355 mask revisions were modified often.



The 1988-LF355 shows only A-revisions.  :-//
There is also a C at the bottom of the die. The older LF355 shows an A.  :-//


Still there is the question whether the Texas-LF355 is a fake or not.  :-//

Offline David Hess

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Re: Opamps - Die pictures
« Reply #43 on: August 23, 2020, 03:52:12 am »
Although the LF355 is the slowest opamp of the LFx5x-family, the capacitors are not as big as possible. I assume 1977 TI wasn´t sure how big they needed the capacitors to get stable operation and because of that they made the possible capacitor area bigger...  :-/O

I am sure they knew exactly how large to make the capacitors.

JFETs have lower transconductance at the same current than bipolar transistors so a smaller compensation capacitor is required yielding a higher slew rate.  Bipolar parts get the same advantage by using transconductance reduction which is why the 741 compensation capacitor is several times larger than later 741 replacements like the MC1458 which use transconductance reduction for exactly this reason.  Transconductance reduction is also what made the 324 so economical; its compensation capacitor is tiny.

So early JFET parts had an inherent size, and therefor cost, advantage over early bipolar parts because they had smaller compensation capacitors.
« Last Edit: August 23, 2020, 03:53:50 am by David Hess »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #44 on: August 23, 2020, 06:34:52 am »
But that doesn't explain why the capacitor area is bigger than actually necessary.
If they had known exactly how big the capacitance had to be, they would have integrated the right size and saved the area as in the National Semiconductor LF355.
I'm pretty sure they didn't use the same die for a bipolar opamp...

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Re: Opamps - Die pictures
« Reply #45 on: August 23, 2020, 07:41:58 am »
JFETs have lower transconductance at the same current than bipolar transistors so a smaller compensation capacitor is required yielding a higher slew rate. Bipolar parts get the same advantage by using transconductance reduction
If you mean that LM324 trick of discarding 75% of the input stage current to ground, then no, not exactly the same. Mind that LM324 is the worst opamp in the world in terms of slew rate, besides ultra low power stuff.

IMO "transconductance reduction" is a big misnomer. In practice, it's just reduction of the input stage current as seen by the VAS, with all the usual consequences: lower gain, higher noise, lower slew rate. I don't know what was the supposed advantage of that over simply making these transistors 4x smaller and running them at 25% current. I can guess that maybe they couldn't make them small enough and the additional grounded collector and additional bias were necessary to clear the base of stored charge acceptably fast.

which is why the 741 compensation capacitor is several times larger than later 741 replacements like the MC1458 which use transconductance reduction for exactly this reason.
Not sure if they do, certainly not Raytheon. They conveniently provided schematics of most of their analog parts and specified 25pF on both versions. Their die photographs don't indicate significant difference in capacitor area either. The RC1458 seems more efficiently packed with less wasted space, though, and its die is only 50% larger.

So early JFET parts had an inherent size, and therefor cost, advantage over early bipolar parts because they had smaller compensation capacitors.
Well, for the record, this LF155 die is huge because of all those silly JFETs whose function could be replicated with 5x smaller bipolars ;) But there are much better JFET opamps out there, like TL072, which packs two channels on about the same area IIRC.

I lost my LF155, maybe Noopy could post exact dimensions?
 

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Re: Opamps - Die pictures
« Reply #46 on: August 23, 2020, 07:56:26 am »
I lost my LF155, maybe Noopy could post exact dimensions?

~ 1,87mm x 1,06mm

 :-+

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Re: Opamps - Die pictures
« Reply #47 on: August 25, 2020, 11:10:58 am »
I don't know what was the supposed advantage of that over simply making these transistors 4x smaller and running them at 25% current.

As explained on page 19 of National Semiconductor application note A, reducing the current to reduce the transconductance also reduces phase margin from the mirror pole and the tail pole, so in that case the compensation capacitance must be *increased* to reduce bandwidth maintaining stability.

https://web.ece.ucsb.edu/Faculty/rodwell/Classes/ece2c/resources/an-a.pdf

Quote
which is why the 741 compensation capacitor is several times larger than later 741 replacements like the MC1458 which use transconductance reduction for exactly this reason.

Not sure if they do, certainly not Raytheon. They conveniently provided schematics of most of their analog parts and specified 25pF on both versions. Their die photographs don't indicate significant difference in capacitor area either. The RC1458 seems more efficiently packed with less wasted space, though, and its die is only 50% larger.

Schematics are usually simplified to not show the transconductance reduction, including the Raytheon RC1458 datasheet I just checked, and I suspect the 741 schematic and values were used instead.  Could a process difference explain the capacitor area you saw?  What really matters is the difference so a 741 on the same process should be compared.

I thought I saw an MC1458 schematic which showed a much lower value of compensation capacitor but now I cannot find it.  Hmm, maybe I was thinking of what sure looks like the MC1458 schematic shown on page 20 of the application note linked above which indicates 5 picofarads instead of the customary 30 picofarads.
 

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Re: Opamps - Die pictures
« Reply #48 on: August 25, 2020, 01:49:31 pm »
So there are three schemes described in this appnote: figure 27, 28a and 28b.

They admit that 28a has a problem with increased noise and 28b may be difficult to fabricate accurately at high "reduction ratio".

Figure 27 could in theory be implemented sneakily in lateral PNP input stages, by increasing parasitic collection by the substrate (which normally is undesirable and efforts are made to prevent it), so you could look at a die and never know that a deliberately introduced, significant substrate collector is there.

But the figure 28 schemes are impossible to realize without additional surface collectors and metal traces hooking them up to the mirror and/or ground. So if a chip exists which uses an "advanced" scheme, we could find it, tear it down and see it. So far I haven't seen anything like that. Not in several 358s, not in the RC4558 from Zeptobars and in Chinese RC4558, not in NJM2068 (a Japanese 4558 on steroids), not in the numerous voltage references posted in "metrology". Nor in this LF155 or TL072, for that matter. If these schemes are used, they probably aren't that very common.

This leaves us with the figure 27 scheme, which is hard to disprove by eyeballing because of the aforementioned possibility of a hidden substrate collector. But we can look at its noise implications. Protest if you think I'm wrong, but I'm quite convinced that noise performance of such input stage is simply equivalent to a normal stage running on n-times reduced bias. I will ignore mirror contribution (imagine that it's sufficiently degenerated or whatever) and look at the LTP.

If I got my math right, transconductance of a mirror loaded LTP equals transconductance of each individual transistor. Noise of an undegenerated BJT happens to be equivalent to the Johnson noise of half its intrinsic emitter resistance (which doesn't have real Johnson noise, obviously), and therefore noise of an LTP conveniently equals the "Johnson" noise of 1/gm. And 1/gm happens to be the reactance of Cc at unity gain frequency, so our math is surprisingly easy.

Take a normal 741 with Cc=25~30pF and GBW=1MHz. That's some 5.5~6kΩ impedance and therefore a hair under 10nV/rtHz LTP noise. Multiply by 1.4 because of the NPN emitter followers and we are at 14nV/rtHz. A real 741 has a hair over 20nV/rtHz IIRC.

Now take the "improved" 741 with 5pF. That's 32kΩ and 22nV/rtHz, even before the 1.4x factor. It simply cannot meet the original spec.

Curiously, Raytheon specifies RC1458 noise similarly to 741, but Motorola's MC1458 density plot shows 40nV/rtHz. Hmm... that puppy may need a teardown.
 

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Re: Opamps - Die pictures
« Reply #49 on: August 26, 2020, 08:24:17 pm »
A little bit more modern: LF411





Sorry, have no size for this one.




It seems that the upper five testpads are used to adjust the absolute value of the offset while the lower three testpads change the polarity of the value. Interesting...
By the way: That´s an interesting transistor type!




The LF411 has four cross connected JFETs at the input.
Nevertheless the offset of the LF411 is a bit higher (7µV/°C typ) than the LF355 (5µV/°C typ)!  :o
I assume the higher integration of the LF411 leads to more temperature depending drift.

Offline magic

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Re: Opamps - Die pictures
« Reply #50 on: August 26, 2020, 09:18:14 pm »
more modern: LF411
:D

By the way: That´s an interesting transistor type!
You bet.
[attachimg=1]
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #51 on: September 23, 2020, 06:00:48 pm »
One more "normal" Opamp, a OP-01:

https://www.richis-lab.de/Opamp18.htm




If you have read my DAC-posts you know the OP-01 from DAC80 and DAC800.
BTW: If you support me on patreon you get a free newsletter! https://www.patreon.com/richis_lab ;)






A nice design...




Here you can see how the differential signal is processed in a crisscross way in the input stage. With this arrangement thermal gradients cause contrary drifts that cancel each other out (of course not perfectly). PMI called it "thermally cross-coupled quad".

Online mawyatt

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Re: Opamps - Die pictures
« Reply #52 on: September 23, 2020, 06:59:10 pm »
One more "normal" Opamp, a OP-01:

https://www.richis-lab.de/Opamp18.htm


If you have read my DAC-posts you know the OP-01 from DAC80 and DAC800.

A nice design...




Here you can see how the differential signal is processed in a crisscross way in the input stage. With this arrangement thermal gradients cause contrary drifts that cancel each other out (of course not perfectly). PMI called it "thermally cross-coupled quad".

George Erdi invented this technique, another brilliant linear IC designer like Bob Widlar. Not only helps with thermal gradients, but also process & stress gradients!!

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #53 on: September 23, 2020, 07:52:54 pm »
The latter only if they affect NPN and PNP in the same way. Dunno if it's the case in practice.

If you like that kind of mazes, try OP07 once ;)
 

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Re: Opamps - Die pictures
« Reply #54 on: September 23, 2020, 08:06:14 pm »
Didn't the early precision parts like the OP-05 and OP-07 use a quad of quads?  I have seen various layouts extending to 8 or 16 cross coupled transistors.
 

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Re: Opamps - Die pictures
« Reply #55 on: September 23, 2020, 08:14:47 pm »


OP-07  :-+




OP-27, also nice!  :-+


Both use quite a lot transistors.


...taken from AD1139:
https://richis-lab.de/DAC07.htm
 
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Offline David Hess

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Re: Opamps - Die pictures
« Reply #56 on: September 23, 2020, 08:28:30 pm »
Both use quite a lot transistors.

And a lot of area for capacitors.

Also notice how the output transistors on one side of the die are lined up with the input transistors on the other side.

 

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Re: Opamps - Die pictures
« Reply #57 on: September 24, 2020, 06:55:54 pm »
Didn't the early precision parts like the OP-05 and OP-07 use a quad of quads?  I have seen various layouts extending to 8 or 16 cross coupled transistors.

Think Erdi came up with the single cross coupled quad concept either at Fairchild or PMI, but don't know about the more complex input transistor layouts.

Best,
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Re: Opamps - Die pictures
« Reply #58 on: September 24, 2020, 07:08:28 pm »
Both use quite a lot transistors.

And a lot of area for capacitors.

Also notice how the output transistors on one side of the die are lined up with the input transistors on the other side.


Lining up the output with input transistors helps create a more uniform thermal gradient wavefront across the chip.

A fun story along these lines was when the IEEE was debating whether a high current 5 Volt linear regulator for TTL logic could be integrated on a single chip. Thermal feedback was what the debate was all about, so they decided to ask Bob Widlar what he thought. The story goes Wilder said, "Of course you can't make a high current 5 Volt single chip linear regulator, thermal feedback will completely mess things up, are you guys completely nuts!!", or something like that. >:D

A few months later National introduced the 1st high current 5 Volt Linear Regulator chip :-DD

Best,
« Last Edit: September 24, 2020, 07:10:57 pm by mawyatt »
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Re: Opamps - Die pictures
« Reply #59 on: September 24, 2020, 11:17:36 pm »
Thermal feedback is also what limits open loop gain of a monolithic operational amplifier, so the symmetrical layout and thermal balancing also increase open loop gain.  This is why it is important to minimize loading on precision operational amplifiers, and why the highest precision parts are also lower power.
 

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Re: Opamps - Die pictures
« Reply #60 on: September 24, 2020, 11:48:42 pm »
I remember seeing an open loop plot of a certain brand 741 op amp that showed the thermal feedback actually caused the + and - inputs to reverse :o

Of course this would normally be squashed by massive external negative feedback, but still not a good op amp parameter :P

Best,
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Re: Opamps - Die pictures
« Reply #61 on: September 24, 2020, 11:57:05 pm »


OP-07  :-+




OP-27, also nice!  :-+


Both use quite a lot transistors.


...taken from AD1139:
https://richis-lab.de/DAC07.htm

Thanks for showing, the OP-07 is my favorite precision GP op-amp, really a well behaved and precise device.

Best,
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~Mike
 

Offline David Hess

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Re: Opamps - Die pictures
« Reply #62 on: September 25, 2020, 12:07:07 am »
I remember seeing an open loop plot of a certain brand 741 op amp that showed the thermal feedback actually caused the + and - inputs to reverse :o

Of course this would normally be squashed by massive external negative feedback, but still not a good op amp parameter :P

In precision applications, the thermal time constant can increase settling time, and may provide the largest contribution to it.

Thanks for showing, the OP-07 is my favorite precision GP op-amp, really a well behaved and precise device.

My favorite is the LT1008/LT1012/LT1097 because of its even lower input bias current.
 

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Re: Opamps - Die pictures
« Reply #63 on: October 14, 2020, 06:59:16 pm »


OP-283
Two Opamps, 5MHz bandwith, single supply 3V-36V, 25mA/30mA output current. The datasheet states the OP-283 as a good microphone and earphone amplifier.




The structures are quite symmetrical but the bondpads are not placed perfectly.
The offset of the mono-opamp OP-183 is laser trimmed. The OP-283 contains two complex resistor areas at the bottom of the die which contain the collector resistors. Probably these resistors are laser trimmed.  :-/O




A lot of signatures? Crowns for the developers? OK...  ;D


https://richis-lab.de/Opamp19.htm


Offline magic

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Re: Opamps - Die pictures
« Reply #64 on: October 14, 2020, 08:47:54 pm »
Interesting way of doing phase summing, it seems they feed input stage currents into the emitters rather than collectors of a current mirror.

Not sure if it really is that great for audio, but likely better than a certain jellybean single supply opamp ;)
 

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Re: Opamps - Die pictures
« Reply #65 on: October 14, 2020, 09:05:23 pm »
Interesting way of doing phase summing, it seems they feed input stage currents into the emitters rather than collectors of a current mirror.

Q3/Q4?
That´s a common base amplifier, right? Good for voltage amplification. Sound like a good solution for a VAS if you add some current amplification? *brainstorming*


Not sure if it really is that great for audio, but likely better than a certain jellybean single supply opamp ;)

Well at least it sounds good in a datasheet.  ;D

Offline magic

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Re: Opamps - Die pictures
« Reply #66 on: October 14, 2020, 09:50:47 pm »
Q3/Q4?
That´s a common base amplifier, right? Good for voltage amplification. Sound like a good solution for a VAS if you add some current amplification? *brainstorming*
Q4 might be consider common base but it doesn't do voltage amplification. It feeds current into the base of Q6 which is roughly constant at two diode drops above the negative rail. Q6 drives Q10 which is the VAS and Q11.

Q3 might be seen as common base too, but it operates in a tight negative feedback loop: increasing Q3 current instantly pulls down Q5 which turns off Q3 base and reduces its current. In fact, Q3 current is almost constant, determined by QB7. Q3 and Q5 simply shift R3 voltage one diode up and apply it to Q4 base, whose emitter applies the original R3 voltage across R4.

This way current variations in Q1 are transferred to the Q2 side. And then Q4 feeds that current imbalance into Q6. That's how I see it.

QB7 and QB8 are of course constant sources. Not sure what's the point of Q7 and Q8 because it seems that Q5 and Q6 collectors could simply be connected to VCC. Maybe something to do with phase reversal prevention or a trick to improve open loop linearity. I don't know, that would take some actual thinking :)
« Last Edit: October 14, 2020, 09:54:31 pm by magic »
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #67 on: October 15, 2020, 03:03:18 am »

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Re: Opamps - Die pictures
« Reply #68 on: October 15, 2020, 11:16:08 pm »
I'm assuming this portion of the discussion is about these transistors in the simplified schematic inside the OP07 datasheet.

If so, my guess is that Q3-Q8 are there to perform input bias current cancellation.

If you go around the loop on 1 side, say the inverting input:
Q2 requires base current (call it Ib2).  Q4 is in the collector path of Q2 to "sample" it and create a replica of Ib2 in its base current since they are both NPN transistors.

I'm assuming Q8 is a PNP like Q6.  Bipolar people love to draw diode connected bipolars as diodes.  Assume Q8 is a diode connected PNP. 
Since they both have the same Veb and the same characteristics, they contribute into that common node a current, (beta+2)*Ib6 (Ib6 from Q6 and (beta+1)*Ib8 from Ib8 and Q6 & Q8 are matched with the same Veb, so Ib8 = Ib6).  That has to equal the replica base current of Q4.

So, we have Ib6 = Ib4/(beta+2) = Ib2/(beta+2).

Q6's collector current, Ic6, is beta*Ib6 = beta/(beta+2) * Ib2 ~ Ib2.

Now you've injected a current into the inverting input of approximately the same value as the actual input current creating a nice cancellation.

I may be a bit off, but I think that's the basic idea.
« Last Edit: October 15, 2020, 11:28:50 pm by P_Doped »
 

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Offline magic

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Re: Opamps - Die pictures
« Reply #70 on: October 16, 2020, 06:56:17 am »
If so, my guess is that Q3-Q8 are there to perform input bias current cancellation.
In the OP07, yes, but see above ;)

There is a die photograph of OP07 a few posts above, you can see that this is pretty much exactly how it works.

There is yet another level of bootstrapped cascode over Q3,Q4 before the signal gets to the emitter followers driving the second stage. I presume it's because otherwise Early effect would break bias cancellation accuracy over input common mode range and reduce input resistance.

Q7,Q5 and Q8,Q6 are two 50:50-ratio split collector lateral PNPs above and below the input cascode block and one collector of each (the input) is also connected to base. Classic IC current mirror trick.
« Last Edit: October 16, 2020, 07:02:29 am by magic »
 

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Re: Opamps - Die pictures
« Reply #71 on: October 16, 2020, 07:14:14 am »
Q3/Q4?
That´s a common base amplifier, right? Good for voltage amplification. Sound like a good solution for a VAS if you add some current amplification? *brainstorming*


Had a quick glance at the schematic, didn't go into details as you did.
To me, Q3/Q4 just look like a folded cascode configuration with the input transistors.
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Offline magic

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Re: Opamps - Die pictures
« Reply #72 on: October 16, 2020, 07:19:52 am »
Folded cascode would have its bases held at constant voltage and collectors loaded with a mirror rather than a pair of equal, stiff current sources. But it's a similar thing in principle, I think.

Here those "cascode" transistors track voltage across R3 and transfer it to R4. At some high frequency, parallel capacitance across R3 kills those voltage swings to eliminate phase delay through the phase summing circuit from the amplifier's forward path, apparently.

edit
Okay, I will try more clearly. In a classic folded cascode amplifier, Q3 transfers Q1 current swings to a PNP mirror above and phase summing occurs between the output of said mirror and Q4. Here, phase summing occurs between R4 and Q4 and Q4 is just a cascode over that node, while the Q3,Q5 circuit is basically a voltage follower, with +1Vbe offset rather than -1Vbe as usual. Observe that Q3 current is fixed by QB7.
« Last Edit: October 16, 2020, 08:04:57 am by magic »
 

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Re: Opamps - Die pictures
« Reply #73 on: October 16, 2020, 08:46:21 am »
I remember seeing an open loop plot of a certain brand 741 op amp that showed the thermal feedback actually caused the + and - inputs to reverse :o

Of course this would normally be squashed by massive external negative feedback, but still not a good op amp parameter :P

Best,
Sounds very dodgy. No negative feedback won't help, because once the + and - inputs reverse, it becomes positive feedback, which will most likely result in latchup.
 

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Re: Opamps - Die pictures
« Reply #74 on: October 16, 2020, 09:56:11 am »
Folded cascode would have its bases held at constant voltage and collectors loaded with a mirror rather than a pair of equal, stiff current sources. But it's a similar thing in principle, I think.

Here those "cascode" transistors track voltage across R3 and transfer it to R4. At some high frequency, parallel capacitance across R3 kills those voltage swings to eliminate phase delay through the phase summing circuit from the amplifier's forward path, apparently.

edit
Okay, I will try more clearly. In a classic folded cascode amplifier, Q3 transfers Q1 current swings to a PNP mirror above and phase summing occurs between the output of said mirror and Q4. Here, phase summing occurs between R4 and Q4 and Q4 is just a cascode over that node, while the Q3,Q5 circuit is basically a voltage follower, with +1Vbe offset rather than -1Vbe as usual. Observe that Q3 current is fixed by QB7.

Yes, indeed. It's not the "classic" folded cascode, the circuit just looks somewhat alike. Transferring voltage from R3 to R4 rings some bells (like ideal / diamond transistor), but I don't recognize a known scheme. Could it be an internal current feedback scheme through R4?
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Offline magic

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Re: Opamps - Die pictures
« Reply #75 on: October 16, 2020, 10:52:40 am »
The point of that is to transfer Q1 current to the Q2 branch of the circuit.

Since Q3 current is constant, it really is not a cascode. Therefore Q1 current has nowhere to go but to R3. This increases/decreases R3 voltage, which is transferred to R4, causing identical increase/decrease in R4 current, which adds to the corresponding opposite change in Q2 current. It's phase summing.

A short way to describe it is that Q3,Q4,Q5 is a resistor-degenerated current mirror biased by two equal collector currents, so in quiescent conditions it simply does nothing besides feeding a current equal to Q5 base current into Q6 base. Then two input stage currents with opposite AC components are fed into the degeneration resistors, resulting in the difference of those currents appearing on Q4 collector.

It's not perfect by the way, because Q4 emitter has nonzero input resistance which to AC currents appears in parallel with R4, so part of the AC current summed at Q4 emitter node escapes through R4 to ground. Depends on the ratio of Q4 intrinsic emitter resistance and R4. R4 can't be too high because if it drops significant voltage, the input transistors will saturate and turn off when their emitters approach ground and likely phase reversal will occur, which this chip is advertised to avoid until some -0.6V. I think the point of this unusual mirror arrangement is to enable operation close to ground and avoid phase reversal below the negative rail.

Current feedback? Dunno. To have feedback, you need to feed something back ;D
What signal is supposed to be fed and from where to where?
« Last Edit: October 16, 2020, 10:56:42 am by magic »
 

Offline magic

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Re: Opamps - Die pictures
« Reply #76 on: October 16, 2020, 11:08:32 am »
I remember seeing an open loop plot of a certain brand 741 op amp that showed the thermal feedback actually caused the + and - inputs to reverse :o

Of course this would normally be squashed by massive external negative feedback, but still not a good op amp parameter :P

Best,
Sounds very dodgy. No negative feedback won't help, because once the + and - inputs reverse, it becomes positive feedback, which will most likely result in latchup.
I think it meant that polarity of thermal feedback itself was positive, i.e. the output going one way affected offset voltage in such way that the output went even harder the same way, in absence of normal feedback.
I suppose it shows up as increased open loop gain and perhaps some phase oddity at extremely low frequencies.
Honestly, not sure what's wrong with it.
 

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Re: Opamps - Die pictures
« Reply #77 on: October 16, 2020, 12:06:49 pm »
The point of that is to transfer Q1 current to the Q2 branch of the circuit.
...
Current feedback? Dunno. To have feedback, you need to feed something back ;D
What signal is supposed to be fed and from where to where?

Read your explanation and studied the schematic - doesn't match.

So, find my fault (or I might be finding it while writing) ;)

If Q1 collector current increases, Q2 collector current is supposed to decrease as their sum is set by QB10.
Increasing Q1 collector current causes R3 voltage to rise.
Decreasing Q2 collector current causes R4 voltage to decrease.
Q3 emitter voltage rising causes its base voltage rising, as Q3 current is constant. Q4 emitter will follow.
Q4 emitter voltage rising increases R4 current, which is opposite to decreasing Q2 collector current.

OK, I've got it now. It's phase summing because these opposite changes add to the desired Q4 collector voltage output. Thanks.

Looks like the output stage (Q10, driven by Q6 through R5) has significant LF voltage gain, too.
Quite a bunch of tricks to achieve single rail operation (input and output range includes "GND"), not that easy to follow.
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Offline magic

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Re: Opamps - Die pictures
« Reply #78 on: October 16, 2020, 04:47:50 pm »
OK, I've got it now. It's phase summing because these opposite changes add to the desired Q4 collector voltage output.
Sorry for the jargon, I've seen it in the Self amplifier book with an implication that it's a common term in opamp literature.
But frankly, I now can't find any example of it on the Internet, so :-//

Anyway, I did indeed mean adding/subtracting the two opposite phase signals from the differential pair.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #79 on: October 25, 2020, 10:23:50 pm »
I had started this High-Power-Opamp-thread: https://www.eevblog.com/forum/projects/opa541-high-power-opamp-die-pictures/
Unfortunately there is a OPA541 in the headline and I got some more High-Power-Opamps.  ;D
In future I will post High-Power-Opamps in this thread.



And now welcome the PA-03:




+/-75V, 30A, max. 500W power dissipation and 1MHz cutoff frequency! That´s a power device!  8)




The PA-03 contains three ceramic carrier (beryllium oxide), a highside powerstage, a lowside powerstage and a circuit to control them.
Apex used a lot of different bondwire diameters.




The powerstages were soldered to the package. After that the controlstage was simply glued down. I assume they wanted to protect the controlstage from the heat of the soldering process.




It seems there are three different resistor types, a shiny one, a thin rough one and a thick rough one.
Of course they did laser tuning.




And there are points to identify the aligment of the masks.




Now that doesn´t look quite robust...  ???




Apex also had problems with the bonding process...




Huuuuuge!  8)
The shunt for overcurrent protection is simply one of the traces leading from a transistor to the output.




It´s a Sziklai-Darlington-powerstage.




That´s a really good temperature measurement! Datasheet states a response time of 10ms.
You can´t kill the transistors with second breakdown. Second breakdown only is a danger at durations longer than 10ms and there the temperature protection is fast enough.  :box:




Input stage is of course a Dual-J-FET for most similar characteristics and a similar temperature.


It´s too late for a longer translation. Please use your favourite translator and take a look at a lot more pictures on my website:

https://www.richis-lab.de/Opamp17.htm

Of course you can ask me whatever you want here in english.

 :popcorn:
« Last Edit: October 25, 2020, 10:49:26 pm by Noopy »
 
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Offline RoGeorge

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Re: Opamps - Die pictures
« Reply #80 on: October 25, 2020, 10:27:34 pm »
APEX?!  Like the game?  :D

Offline Noopy

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Re: Opamps - Die pictures
« Reply #81 on: October 25, 2020, 10:28:58 pm »
I´m getting old. Didn´t know there is a game with the name APEX.  ;D :-+

Offline T3sl4co1l

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Re: Opamps - Die pictures
« Reply #82 on: October 26, 2020, 01:11:51 am »
They had the name before the game existed.  8)

Handle that thing carefully, those are BeO substrates!  Fantastic heat conduction, worth every cent too... ;D

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #83 on: October 26, 2020, 04:16:49 am »
Thanks for the hint. It´s not the first BeO-part I have opened. I take care not to cut the ceramic that should be good enough.  :-/O

Offline Noopy

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Re: Opamps - Die pictures
« Reply #84 on: November 02, 2020, 10:14:54 pm »


Let´s look into the famous LM709.




That are very small resistor strings! I have never seen such small resistors (with respect to the transistors).




The pnp-transistor Q9 shows the normal structure of a pnp-transistor manufactured with a npn-process.
But the pnp-transistor Q13 is different! There is a brown emitter area surrounded by the blue, n+ doping. You can´t see a collector. It seems like Q13 uses the substrate as collector. That´s possible because the collector had to be connected to the negative supply. The buried n+ layer was certainly removed. The n+ base contact frame gives you a quite low resistance leading to the active base area.
It would have been possible to use the isolation diffusion as collector but then the base area would have been too long for a good transistor.


https://www.richis-lab.de/Opamp20.htm

 :-/O
 
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Offline David Hess

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Re: Opamps - Die pictures
« Reply #85 on: November 03, 2020, 01:31:55 am »
But the pnp-transistor Q13 is different! There is a brown emitter area surrounded by the blue, n+ doping. You can´t see a collector. It seems like Q13 uses the substrate as collector. That´s possible because the collector had to be connected to the negative supply. The buried n+ layer was certainly removed. The n+ base contact frame gives you a quite low resistance leading to the active base area.

That sounds suspiciously like a charge storage PNP.  Widlar himself describes it on page 3 of Linear Technology application note 16:

https://www.analog.com/media/en/technical-documentation/application-notes/an16f.pdf
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #86 on: November 03, 2020, 03:54:39 am »
But the pnp-transistor Q13 is different! There is a brown emitter area surrounded by the blue, n+ doping. You can´t see a collector. It seems like Q13 uses the substrate as collector. That´s possible because the collector had to be connected to the negative supply. The buried n+ layer was certainly removed. The n+ base contact frame gives you a quite low resistance leading to the active base area.

That sounds suspiciously like a charge storage PNP.  Widlar himself describes it on page 3 of Linear Technology application note 16:

https://www.analog.com/media/en/technical-documentation/application-notes/an16f.pdf

Thanks for the hint, that´s very interesting.  :-+

I hope I got it right:
Usually you try to minimize base-emitter-capacitance to get a fast transistor (fast switch-off).
In the charge storage PNP-transistor you try to get a bigger base-emitter-capacitance with fast charges so you can boost a signal through this area. (I suppose switch off is slower.)
In the LM709 output stage that would speed up the lowside getting low. I assume a slower switch off speed is not extremly important because the highside can pull the output upwards.

Offline Noopy

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Re: Opamps - Die pictures
« Reply #87 on: November 05, 2020, 09:00:22 pm »


Mikroelektronika Botevgrad 1УO709 - 1UO709, another 709-opamp.




Unfortunately the die was damaged a little.
Nevertheless we can clearly see that it is very similar to the LM709.


https://www.richis-lab.de/Opamp21.htm


 :popcorn:

Offline Noopy

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Re: Opamps - Die pictures
« Reply #88 on: November 09, 2020, 03:39:34 pm »
Let´s take a closer look into a OPA627!  8)





The die is quite big (2,9mm x 2,0mm).




The most interesting part is the input stage. There is a matrix of 2x8 transistors forming the two input transistors. Burr-Brown tried to match the metal traces and the silicon traces as good as possible. In the upper left corner there are two green underpasses which are "very" long and wide just to match the underpasses in the lower right corner.

Around the input transistors there are the tuned resistors for input-offset tuning and the current mirror emitter resistors which travel quite a long way to get to the left edge of the die. I assume they wanted to bring some distance between the transistors and the edge of the die and then decided to fill the empty room with the current mirror resistors.

On the right side there are four transistors generating the two cascode transistors of the input stage. The current sink is placed in the center for most equal temperatures.

Above and below the input transistor matrix there are two more input-J-FETs which are connected to two more transistors in the cascode stage.




The circuit is a bit different to the schematic in the datasheet. I dont´really understand what is the purpose of the path Q17/Q18-Q6/Q7...  :-// @magic: any ideas?  ;)


More pictures here:
https://www.richis-lab.de/Opamp22.htm

 :popcorn:
 
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Offline David Hess

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Re: Opamps - Die pictures
« Reply #89 on: November 09, 2020, 04:18:25 pm »
The circuit is a bit different to the schematic in the datasheet. I dont´really understand what is the purpose of the path Q17/Q18-Q6/Q7...  :-// @magic: any ideas?  ;)

Could that be transconductance reduction of the input stage?  It is not in the form that I usually see and it is almost always left off of published schematics.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #90 on: November 09, 2020, 06:46:19 pm »
Could that be transconductance reduction of the input stage?  It is not in the form that I usually see and it is almost always left off of published schematics.

That's possible.  :-+ ...an interesting way of transconductance reduction. Probably a very clever way for the OPA627.  :-//

Offline magic

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Re: Opamps - Die pictures
« Reply #91 on: November 09, 2020, 08:46:21 pm »
If the schematic is to be believed, these are P channel JFETs like in TL071 so you have drawn them upside down. The sources should be "up", the drains should be "down".

Then it looks like Q17,Q18 are simply source followers and Q6,Q7 diodes shift the voltage one Vbe up and drive bases of Q2~Q5. Input stage current is about 8x the current through Q6,Q7 and Q17,Q18, which is set by that current source at the positive rail.

Q8 and Q1 plus something between them (let me guess: a string of diodes or resistor) bootstrap the drains of all those JFETs.

BTW, zeptobars has a higher resolution image.
https://zeptobars.com/en/read/BB-TI-OPA627-opamp-genuine-fake
« Last Edit: November 09, 2020, 08:50:41 pm by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #92 on: November 10, 2020, 04:25:48 am »
Thanks!  :) You are right, the JFETs were rotated. And the numbers were also confusing. I changed that:



Is it correct to call J1-J8/Q2-Q3 a cascode?

I didn´t check the parts between Q8 and Q1 but that should be some kind ob voltage drop.  :-+

That´s an interesting input stage! But why did they double the inputs? Why J17/J18 and Q6/Q7?


I know zeptobars had already pictures but I had to take a look into this one because the owner wanted to know whether it´s genuine.  :-/O

Offline magic

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Re: Opamps - Die pictures
« Reply #93 on: November 10, 2020, 10:16:52 am »
Not sure. Q6 seems to have ⅛ emitter area of Q2+Q3 and J17 is ⅛ of J1~J8 and the resistors are probably in 8:1 ratio too. These two current paths operate almost identically. The only difference I see so far is that Q6 and J17 current is affected only by Early effect in the current source, but Q2+Q3 and J1~J8 current is affected also by Early effect in Q2+Q3.

Is this difference between J17 and J1~J8 operating current significant? Maybe for THD, or maybe not. Maybe this configuration only plays some role in preventing phase reversal. Maybe they didn't want to do a thermally balanced layout for Q6. Maybe it avoids needing to laser trim R7. Maybe simulation would show something.

BTW, if we connect Q6 emitter to Q2+Q3, we get a configuration analogous to inverted LM101A.
« Last Edit: November 10, 2020, 10:21:57 am by magic »
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #94 on: November 10, 2020, 12:08:45 pm »
Thanks for your interpretation!
A mysterious input stage...  :-/O

Offline David Hess

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Re: Opamps - Die pictures
« Reply #95 on: November 10, 2020, 04:37:47 pm »
Is it correct to call J1-J8/Q2-Q3 a cascode?

Yes, I was looking at it completely wrong.  Q2 through Q7 are the cascode transistors for J1 through J8 and J9 through J16.

Quote
That´s an interesting input stage! But why did they double the inputs? Why J17/J18 and Q6/Q7?

J17 and J18 control the base voltage of the cascodes so that they follow the input JFETs making Vds is constant.  The base connection between Q6 and Q8 receives a constant current from the positive supply which creates a constant voltage across R7 and R8.  Q6 and Q7 are connected as diodes so that their Vbe compensates the Vbe of the cascode transistors.

A cascode configuration is common with super-beta input stages because the Vce breakdown voltage is very low, only like 3 to 5 volts.  Sometimes it is used to increase the differential input voltage range by preventing breakdown of base-emitter junction of the input transistors.  I do not know why it would be used with JFETs unless modulation with changing drain voltage was a significant error term, which it could be.  Or maybe these JFETs have a limited maximum Vds?
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #96 on: November 10, 2020, 05:20:55 pm »
That´s an interesting input stage! But why did they double the inputs? Why J17/J18 and Q6/Q7?

J17 and J18 control the base voltage of the cascodes so that they follow the input JFETs making Vds is constant.  The base connection between Q6 and Q8 receives a constant current from the positive supply which creates a constant voltage across R7 and R8.  Q6 and Q7 are connected as diodes so that their Vbe compensates the Vbe of the cascode transistors.

A cascode configuration is common with super-beta input stages because the Vce breakdown voltage is very low, only like 3 to 5 volts.  Sometimes it is used to increase the differential input voltage range by preventing breakdown of base-emitter junction of the input transistors.  I do not know why it would be used with JFETs unless modulation with changing drain voltage was a significant error term, which it could be.  Or maybe these JFETs have a limited maximum Vds?

That is convincing, thanks!  :-+

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Re: Opamps - Die pictures
« Reply #97 on: November 10, 2020, 05:33:32 pm »
I wonder what advantages this topology would have in a discrete design, with JFET (or bipolar) followers driving common-base bipolars to make a differential input stage.  Noise will be higher.

Incidentally, some people object to calling it a cascode and consider it a cascade (?) when it is the emitter or source of the input transistor driving the emitter or source of a cascode transistor and the transconductance is controlled by the emitter and source resistances plus any added resistance as in this case.

If you squint a little, then it is a differential pair made up of complementary transistors and in this case, completely different types of transistors.  I have run across this complementary differential pair before in high frequency and high frequency high voltage circuits.
« Last Edit: November 10, 2020, 05:35:23 pm by David Hess »
 

Offline Kleinstein

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Re: Opamps - Die pictures
« Reply #98 on: November 10, 2020, 06:02:08 pm »
Keeping the DS voltage of the input JFETs about constant also helps getting a constant and reduced input capacitance. With conventional JFET OPs the bootstrapping may extend to not just the drain voltage, but also to the isolation from the substrate.  AFAIK the OPA627 is a kind of SOI device and does not use the conventional junction isolation, so it would not need this extra step.

One weakness of JFET amplifier is a voltage dependent input capacitance that can create THD.
 

Offline magic

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Re: Opamps - Die pictures
« Reply #99 on: November 10, 2020, 06:15:55 pm »
Indeed, high source impedance and variable input capacitance form a variable RC lowpass which (slightly) attenuates positive and negative half-cycles by different amount and distorts the waveform.

OPA6x7 are clearly advertised as dielectric-isolated ICs and have long been known as good performers in this regard. More recently, TI claims that OPA140/OPA1641 offer similar performance. Perhaps they came up with some cheaper SOI process.

Bipolar opamps have similar problems with high source impedance. Their BC capacitance isn't constant and neither are base currents.
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #100 on: November 10, 2020, 07:31:35 pm »
Incidentally, some people object to calling it a cascode and consider it a cascade (?) when it is the emitter or source of the input transistor driving the emitter or source of a cascode transistor and the transconductance is controlled by the emitter and source resistances plus any added resistance as in this case.

Just to be clear (after taking one more closer look):
J1-J18 and Q2-Q7 don´t form a cascode but a cascade.
The whole circuit has a similar effect: It hold´s the DS voltage of the input transistors constant but it´s no cascode.

Does everybody agree with me?  :-+

Offline Noopy

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Re: Opamps - Die pictures
« Reply #101 on: November 13, 2020, 01:08:10 pm »
I have taken pictures of the side of the OPA627-die:




I pretty sure the gap directly under the surface is the dielectrical isolation.  :-/O




Here another OPA627-die. The upper die is ~20µm thick. The whole stack is 250µm high.

 :-/O
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #102 on: November 13, 2020, 02:17:42 pm »
Old SOI processes were pretty crude, involving the following steps:

- etching deep trenches on the top side and filling them with silicon oxide
- covering the whole top surface in silicon oxide
- growing hundreds µm of polycrystalline silicon or thermally fusing another wafer on top
- flipping everything upside down
- precisely grinding away almost all of the original wafer until the isolation trenches are exposed

This die looks like it may have been produced that way. I think it's a big part of why those old BB chips are still one of the most pricey opamps around.
 
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Offline Noopy

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Re: Opamps - Die pictures
« Reply #103 on: November 13, 2020, 03:02:54 pm »
Old SOI processes were pretty crude, involving the following steps:

- etching deep trenches on the top side and filling them with silicon oxide
- covering the whole top surface in silicon oxide
- growing hundreds µm of polycrystalline silicon or thermally fusing another wafer on top
- flipping everything upside down
- precisely grinding away almost all of the original wafer until the isolation trenches are exposed

This die looks like it may have been produced that way. I think it's a big part of why those old BB chips are still one of the most pricey opamps around.

Very interesting! Thanks for the Explanation!  :-+

Offline Noopy

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Re: Opamps - Die pictures
« Reply #104 on: November 15, 2020, 05:30:09 am »
Here some older pitctures of a LM741:





https://www.richis-lab.de/Opamp23.htm

I already had uploaded the pictures in my Gould 4074 teardown but I need the chapter for the next opamp...  :-/O ;)

Offline Noopy

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Re: Opamps - Die pictures
« Reply #105 on: November 16, 2020, 12:25:22 pm »


The "next opamp" is a LH0042, a J-FET-input Hybrid-Opamp.




The LH0042 is built with two dies (J-FET-input and the rest of the opamp) on a ceramic substrate.




On the small die there are two J-FETs apparently built by National Semiconductor.




The second die is a modified LM741-die.




Here you can see the differences.
The actual circuit around Q8 is a little different to the LM741-schematic (no current mirror) but in the LH0042 it is missing completely. The J-FET-die is placed on an area of the positive supply.
The input transistors Q1/Q2 are missing so that the J-FETs can control the cascade transistors Q3/Q4.


https://www.richis-lab.de/Opamp24.htm

 :-/O
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #106 on: November 16, 2020, 05:52:42 pm »
That's fishy, 741 circuit can't work correctly without the Q8/Q9 mirror, it's critical for regulating input stage current.
It looks like they included additional small collectors on Q3/Q4 and connected them to the base, like in LM101A. Then the input stage is fine.
And it seems they cheated and did the same thing on LM741 too.

edit
Perhaps the rest of the circuit is LM101A too. You could try LM107 - an LM101A with internal compensation. It may be the same silicon, with Q1/Q2 connected normally but Q8 disconnected and bypassed.
« Last Edit: November 16, 2020, 06:07:56 pm by magic »
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #107 on: November 16, 2020, 06:10:01 pm »
You are right there are two collectors on Q3 and Q4 and one of each is connected to their common base. (in the LH0042 and in the LM741)

You can find that circuit in the schematic of the LM148 which provides four LM741:




Can you explain to me why exactly the Q8/Q9 is neccesary? At first sight I would say a constant current through the base of Q3/Q4 gives a constant current sum in the differential amplifier so everything is ok?  :-// But the base-collector connection will prevent saturation of Q3/Q4, right?


BTW: NS has printed three different schematics for the LM741 (LM741, LH0042 and LM148). In every schematic the circuit is a little bit different (ignoring the J-FET input in the LH0042).

Offline magic

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Re: Opamps - Die pictures
« Reply #108 on: November 16, 2020, 07:03:38 pm »
Maybe it could work, but Q10 current would need to be reduced by beta of Q3/Q4. And then input stage current would depend on beta of Q3/Q4, which is subject to random production variation and thermal drift. Actually, I think the original 101 may have worked that way but later the 741 and 101A types used more complex biasing to improve input stage regulation.
 

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Re: Opamps - Die pictures
« Reply #109 on: November 16, 2020, 07:07:56 pm »
You are right there are two collectors on Q3 and Q4 and one of each is connected to their common base. (in the LH0042 and in the LM741)

That configuration is used by the LM301A as part of the improvement over the LM301 to control input bias current.  Wouldn't National have used their own chip instead of Fairchild's?

Quote
You can find that circuit in the schematic of the LM148 which provides four LM741

The 5 picofarad compensation capacitance indicates that input stage transconductance was reduced which might be backed up by lower input bias current.  I wonder if the LM148 schematic is complete since Q8 should not be needed; see below.

Quote
Can you explain to me why exactly the Q8/Q9 is necessary? At first sight I would say a constant current through the base of Q3/Q4 gives a constant current sum in the differential amplifier so everything is ok?  :-// But the base-collector connection will prevent saturation of Q3/Q4, right?

Q8 and Q9 make the current pulled out of the bases of Q3 and Q4 constant so the input bias current is constant over the input common mode range.  As the input common mode voltage rises, in bias current rises, increasing current through Q8 and Q9, so less current is provided by the base connections to Q3 and Q4, and input bias current is restored.

Contrast that with the LM301 which lacked that circuit and had a wider range of input bias current, which was improved in the LM301A.

If anybody has a copy of Widlar's paper on the LM301A, I would like to see it.  All I find are references to its existence - Robert J. Widlar, “IC Op Amp with Improved Input-Current Characteristics,” IEEE, December 1968.
 
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Offline magic

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Re: Opamps - Die pictures
« Reply #110 on: November 18, 2020, 11:02:33 am »
Actually I was wrong: input stage current of the original LM101 was not that completely uncontrolled. Base current of Q3/Q4 was generated by mirroring base current of another (presumably similar) PNP, whose collector current was regulated, albeit poorly so and with negative thermal coefficient.

I don't think Widlar's paper exists anywhere on the Internet, but plausible explanations of LM101, LM741 and LM101A circuitry are found here:
http://www.ee.bgu.ac.il/~angcirc/History/Solutions_2003_2004_B/SomeStuff/History18opamp.pdf
 
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Offline djerickson

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Re: Opamps - Die pictures
« Reply #111 on: November 19, 2020, 01:34:01 am »
I'd like to see a photo of LT1013. Precision dual, single supply, multi-sourced, and low cost. Almost a perfect part, BUT.... The SOIC pinout is not standard, I assume because the die had to be rotated to fit the SOIC8 package. So instead I pay lots more for OP279s.   So sad:(
Dave
 

Offline Noopy

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Re: Opamps - Die pictures
« Reply #112 on: November 19, 2020, 04:12:00 am »
I'd like to see a photo of LT1013. Precision dual, single supply, multi-sourced, and low cost. Almost a perfect part, BUT.... The SOIC pinout is not standard, I assume because the die had to be rotated to fit the SOIC8 package. So instead I pay lots more for OP279s.   So sad:(
Dave

I will look for one.  :-+

Offline David Hess

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Re: Opamps - Die pictures
« Reply #113 on: November 20, 2020, 12:43:40 am »
I'd like to see a photo of LT1013. Precision dual, single supply, multi-sourced, and low cost. Almost a perfect part, BUT.... The SOIC pinout is not standard, I assume because the die had to be rotated to fit the SOIC8 package. So instead I pay lots more for OP279s.

The LT1013 was not the only older dual part to suffer from that problem in the SOIC package.  Linear Technology later released newer parts with similar performance and smaller dies but as you note, the LT1013 is the one with multiple sources making it the low cost choice.
 

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Re: Opamps - Die pictures
« Reply #114 on: November 21, 2020, 02:06:48 pm »
I'd like to see a photo of LT1013. Precision dual, single supply, multi-sourced, and low cost. Almost a perfect part, BUT.... The SOIC pinout is not standard, I assume because the die had to be rotated to fit the SOIC8 package. So instead I pay lots more for OP279s.   So sad:(
Dave
I will look for one.  :-+

I have the LT1013 in the line. Next decap session I will put it into the ofen.  :-+


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