Author Topic: Opamps - Die pictures  (Read 6891 times)

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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 ;)
 

Offline David Hess

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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.
 

Offline Noopy

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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.

 

Online mawyatt

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

Online mawyatt

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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 »
Research is like a treasure hunt, you don't know where to look or what you'll find!
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Offline David Hess

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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.
 

Online mawyatt

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

Online mawyatt

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

Offline Noopy

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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 ;)
 

Offline Noopy

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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 »

Offline P_Doped

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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 »
 

Offline Noopy

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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 »
 

Offline capt bullshot

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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 »
 

Offline Zero999

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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.
 

Offline capt bullshot

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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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