Author Topic: Opamps - Die pictures  (Read 18399 times)

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Online 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?  :-+

Online 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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Online 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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Online 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!  :-+

Online 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 ;)

Online 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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Online 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 »
 

Online 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).

Online 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.
 

Offline David Hess

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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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Online 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
 

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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.
 

Online Noopy

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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.  :-+

Online Noopy

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Re: Opamps - Die pictures
« Reply #115 on: December 12, 2020, 08:47:36 pm »
(The LT1013 will come soon!)




Today I have a КP597CA1 (KR597SA1) for you, a soviet AM685 clone.
The brown package isn´t lightproof. That can be a problem if you want to compare values with small differences and the light is fluctuating...  >:D




The brown material isn´t easy to remove...




...but the picture is good enough to identify every component.


More pictures here:

https://www.richis-lab.de/Opamp25.htm

 :-/O

Online Noopy

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Re: Opamps - Die pictures
« Reply #116 on: December 22, 2020, 09:52:21 pm »
I'd like to see a photo of LT1013.


Done that:






There is some silicone potting on the die.




A different part and the die is still in the package.




The die is 2,4mm x 1,9mm.




The design dates back to 1987, manufactured in 2000.




The pink part makes it possible to got down to 0V (with single supply).
Datasheet explains that with other opamps negative voltages on one input of such an input stage can lead to a phase reversal. In my view phase reversal is not really the right naming. With negative voltages the differential amplifier (dark green) can be driven into saturation and so the whole circuit is buggy. The output goes high but that´s not really a phase reversal. In the LT1013 the transistors Q21/Q22/Q27/Q28 supply current to the input stage as soon as the voltage is low enough so there is no saturation problem in the following stage.
There is a small mistake in the datasheet schematic. Q28 is connected to the positive supply.
I´m not perfectly sure what the grey part does. In my view you need these components if you drive the differential stage to hard. The next stage can only source current so too much current has to be drained over Q29/Q8. Q9/Q11/Q12/Q13 compensates the current in the left leg.
The VAS (and it´s drivers Q10/Q18) is cyan.
Steering of lowside-output-transistor Q34 is realized by the yellow part. Quite interesting constellation.
The right blue part generates reference voltages. There are a lot of current mirrors generating the currents for the different stages.
The green part is an overcurrent protection.




Most of the parts can be identified on the die.
Interesting that there is a second V+ bondpad...  :-//




The input stage is quite symmetrical and partly cross wired.
The input resistors are placed in parallel too.




That´s interesting. The emitter resistors of the current sources of the input stage can be adjusted (offset adjust).
There are two long resistors. In the red path you can switch in a 2R, a R, a R/2 and a R/4 resistor giving you 16 steps of adjustment. In addition in the green path there is a 4R resistor for inverting the adjustment.
But wait! There are five fuses but only three testpads and one bondpad!  ??? It seems like they found a way to cut only one fuse although there are two in series.




It seems like the metal layer on the green resistors makes it possible to do some bigger adjustment if necessary.




I used my very special simulation tool MS Powerpoint to show the thermal gradients.  ;D
Well you can imagine that the placement of the input transistors is optimized so they see very little temperature difference which gives you low offset drift.




Also very interesting are the capacitors. The 21pF- and the 2,5pF-capacitor are obvious and built like we now integrated capacitors.
But there are a lot of other capacitors which need a lot more area. Thankfully these capacitors are reffered to ground. To reduce the necessary silicon area the capacitors are integrated under the active areas. You can see a green frame, that´s the capacitor.




In the lower right corner there is a metal-fuse and a testpad which doesn´t interact with the circuit. I assume that´s a kind of binning...  :-//


More pictures here:

https://www.richis-lab.de/Opamp26.htm

 8)
 
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Offline David Hess

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Re: Opamps - Die pictures
« Reply #117 on: December 23, 2020, 05:16:38 am »
There is some silicone potting on the die.

Analog ICs require a compliant encapsulation inside of a plastic package to prevent strain on the die from ruining precision.

I remember hearing a story that the managers at National kept asking why linear IC packaging had to cost more and why couldn't they use the cheaper packaging for digital ICs.  Then a management genius shifted packaging to the digital IC group without telling the engineers and a couple months later all of their linear ICs started failing testing, so they were without analog ICs to sell for several months and ended up buying analog ICs where possible from competitors to fulfill orders.
 
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Online magic

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Re: Opamps - Die pictures
« Reply #118 on: December 23, 2020, 09:02:15 am »
I´m not perfectly sure what the grey part does.
My guess: Q13,Q14 generate equal current as Q16 and Q11 base current mirrored by Q12 into Q7 collector makes up for Q7,Q8 base current. Q12 also maintains Q11 Vce at similar level as Q7,Q8. Ideally Q11 would have equal area as Q7+Q8, it seems they didn't bother.
Similarly, Q9 base connected to Q7 collector balances Q10 base current drawn by Q8 collector. This trick is present in LM358, even if not shown on most schematics.
 
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Online Noopy

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Re: Opamps - Die pictures
« Reply #119 on: December 23, 2020, 09:57:18 am »
As always I´m glad for your input, magic.  :-+
Let me check your points one by one:

Q13,Q14 generate equal current as Q16 and Q11 base current mirrored by Q12 into Q7 collector makes up for Q7,Q8 base current.
Sounds quite reasonable.  :-+
But how can you be sure that the current through Q11/Q9 (which is mirrored into base of Q7/Q8) is equal to the base current of Q7/Q8?


Q12 also maintains Q11 Vce at similar level as Q7,Q8.
But Vce of Q7 is Vbe of Q7, isn´t it?
Vce of Q11 is Q11_Vbe + Q12_Vbe.  :-//


Similarly, Q9 base connected to Q7 collector balances Q10 base current drawn by Q8 collector. This trick is present in LM358, even if not shown on most schematics.
You wanted to write "Q29 base connected to Q8 collector...", didn´t you?
Current flowing from "outside" (Q10) into the right leg of the differential amplifier is steering Q29 which gives us more current in the left leg of the current mirror. That gives us more current in the right leg, where the current out of Q10 is compensated and because of that nobody in the upper part of the differential amplifier is bothered by Q10. Is that correct?

Offline exe

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Re: Opamps - Die pictures
« Reply #120 on: December 23, 2020, 12:29:57 pm »
all of their linear ICs started failing testing, so they were without analog ICs to sell for several months and ended up buying analog ICs where possible from competitors to fulfill orders.

I heard this story too and I wonder how realistic it is. How likely that parts from competitors meet same specs like noise, bias, drift, and other parameters?
 

Offline daqq

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Re: Opamps - Die pictures
« Reply #121 on: December 23, 2020, 12:41:34 pm »
Quote
How likely that parts from competitors meet same specs like noise, bias, drift, and other parameters?
Depending on the product could easily be true. The OP07 op amp is made by Ti and Analog currently, at the time was likely made by more. Pretty much everyone makes the venerable 741 or other jellybean op amps. The LM399 is made by both Analog and some time ago was made by National Instruments as well. Also a compatible part was made by Tesla (Czechoslovakia), MAB399.

There may be some minor differences, but they should be drop in replacements.
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Online magic

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Re: Opamps - Die pictures
« Reply #122 on: December 23, 2020, 03:45:36 pm »
I have done some quick and dirty testing of voltage noise in a few opamps (including 553x, 4558, and yes, OP07) and TI tends to have a bit more 10Hz noise than competitors like Analog, vintage Philips, JRC, whichever applicable.
Nothing out of spec, but if you expect parts better than 1970's specs, prepare for |O
TI has some impressive low noise parts on modern processes, but their jellybeans simply didn't look that great in my tests. Observe that they rarely publish typical noise spectrum plots for those parts.

how can you be sure that the current through Q11/Q9 (which is mirrored into base of Q7/Q8) is equal to the base current of Q7/Q8?
Only base current of Q11 is mirrored, and collector current of Q11 appears equal to the total current through Q7 and Q8.

Similarly, Q9 base connected to Q7 collector balances Q10 base current drawn by Q8 collector. This trick is present in LM358, even if not shown on most schematics.
You wanted to write "Q29 base connected to Q8 collector...", didn´t you?
Current flowing from "outside" (Q10) into the right leg of the differential amplifier is steering Q29 which gives us more current in the left leg of the current mirror. That gives us more current in the right leg, where the current out of Q10 is compensated and because of that nobody in the upper part of the differential amplifier is bothered by Q10. Is that correct?
I think Q9 balances Q10 like in LM358 (caution: different numbering below).


I'm not sure what exactly Q29 is trying to achieve, but it only feeds some base current into Q7,Q8 so its own base current should be comparatively lower.
 
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Offline exe

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Re: Opamps - Die pictures
« Reply #123 on: December 23, 2020, 03:55:34 pm »
TI has some impressive low noise parts on modern processes, but their jellybeans simply didn't look that great in my tests. Observe that they rarely publish typical noise spectrum plots for those parts.

That's what I heard on multiple occasions, presumably due to die shrinkage (smaller transistors == more noise, afaik). Still, please post some data and how you measured it if you have them. That's because most people who make such claims don't provide details, and I'm a bit suspicious for claims without data, esp. when people talk about audio amplifiers. So much audiopholery around :(.
 

Online Noopy

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Re: Opamps - Die pictures
« Reply #124 on: December 23, 2020, 09:13:51 pm »
I think now I'm on the right track:
- Q29 is necessary to transfer the base potential of Q10 to Q9.
- Q9 removes the Vbe of Q29.
- Q11 acts like Q10 because
   - it conducts the same current (current sources Q13 and Q14),
   - Q11 (NPN) emitter potential is the same as Q10 (PNP) base potential
- Base current of Q11 will be similar to base current of Q10. Q12 just has to mirror this current into the left leg of the differential amplifier to compensate Q10.


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