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AD797 schematic
AD797 schematic
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Old 14th April 2018, 05:42 PM   #1
myhrrhleine is offline myhrrhleine  Belize
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Default AD797 schematic

hello, I am looking for a schematic of the AD797.
Not the data sheet but the full schematic, please. tia
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Old 14th April 2018, 06:43 PM   #2
DPH is online now DPH  United States
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You need to be a bit more thorough with your searches:
Class A biasing for the AD797?

Is the closest I remember. "jcx" and "ad797" gets you pretty far though.
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Old 15th April 2018, 05:41 PM   #3
myhrrhleine is offline myhrrhleine  Belize
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yes, I do need to be more thorough, but I do need help please.
That link did not help me.
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Old 15th April 2018, 09:32 PM   #4
Elvee is offline Elvee  Belgium
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Scott Wurcer, the designer of the chip is a member of the forum.
If he is inclined to, he may give you first-hand information; let's hope this thread catches his attention....
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Old 15th April 2018, 09:42 PM   #5
DPH is online now DPH  United States
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Quote:
Originally Posted by myhrrhleine View Post
yes, I do need to be more thorough, but I do need help please.
That link did not help me.
Just to be sure, you saw the .asc at the bottom? Scott's own comments were that JCX got pretty close. There's the AES preprint describing the circuit design, but I haven't read it.

There's still relevant reasons AD wouldn't want to have every last bean spilled about it, even ~30 years later, as it's still one of their highest performing precision, low noise opamps.
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Old 15th April 2018, 11:29 PM   #6
scott wurcer is offline scott wurcer  United States
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This was published at the AES, the bias currents are all ordinary current sources and the Ib comp and null are not shown but they are nothing special. I have retired and all my archives are no longer with me. If you have a question I can probably answer it here.
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Old 16th April 2018, 12:19 AM   #7
scott wurcer is offline scott wurcer  United States
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Funny I never noticed before, I used VCC and VSS where typically you would use VCC with VEE and VDD with VSS.
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Old 16th April 2018, 01:35 AM   #8
tomchr is offline tomchr  Canada
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Intriguing with the circuit around Q23 and associated bits. Is that a saturation clamp of sorts?

Tom
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Old 16th April 2018, 02:12 AM   #9
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by tomchr View Post
Intriguing with the circuit around Q23 and associated bits. Is that a saturation clamp of sorts?

Tom
Q23 is just a cascode for Q19. There are clamps in the current mirror shown for both + and - misbehavior (Q50, Q64).

EDIT - Obviously C2 does not go to chassis ground, I honestly don't remember how the metal layers and parasitics were actually wired.
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Old 16th April 2018, 02:54 AM   #10
tomchr is offline tomchr  Canada
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Are Q18 and Q19 then biased at current densities similar to Q15 and Q16/17 to bias the clamp?

Tom
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