Opamps - Die pictures

[Noopy]

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

 

[magic]

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.

[Noopy]

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. 

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...

[Noopy]

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.

[David Hess]

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.

[magic]

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

[Noopy]

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. 

[magic]

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.

[Noopy]

You are right. The bias circuit is very different, less complex:



 

[David Hess]

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.

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.

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.

[Noopy]

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...

 

[magic]

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

[Noopy]

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. 

[magic]

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

[Noopy]

Yes, the right mixture of negative feedback and feedforward. That's the trick.
What's LB-17?

[magic]

The NatSemi paper about LM118/318 which I mentioned before.

[Noopy]

Of course! Sorry, I was confused somehow. 

[SeanB]

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.

[Noopy]

More coming soon! 

[David Hess]

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.

[Noopy]

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. 

[Hydron]

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).

[Noopy]

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!

[magic]

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.

[macboy]

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.