Insane op-amp

150

01:57:55

It's a fine op-amp, but look at the power supply! :D

Inputs are marked by switches:
* push-button: non-inverting input (+in)
* SPST: inverting input (-in)
The output is orange.

Gain: 49,800x (94dB)
Offset: -1.2mV

All the gain happens in the long-tailed pair. The ridiculous voltage levels make that possible. I made gain ten times higher with 100kVx2 power and 30MΩ resistors in the long-tailed pair, but it took like 10 minutes to reach operating conditions. Actually, it did and then it didn't, and then it did again, and I have no idea why. 

It's very slow, anyway. 3kHz is about its limit.

Connecting ground through a closed SPST is another way to prevent convergence errors at startup. Serendipitous discovery today.

published 7 years ago

jason9

7 years ago

It’s hardly rail to rail though, stopping at 3.1kV and 3.7kV (for negative and positive). I didn’t know about the spst switch though. Good to know!

eekee

7 years ago

@jason9: I know! :D In fact I originally built it with +-10V supplies. Output clipped at, if I remember right, +5.6V and -5V.

eekee

7 years ago

@jason9: Sometimes a switch doesn't prevent convergence errors but a capacitor does. I've no idea why.

jason9

7 years ago

Weird.

jason9

7 years ago

Have you checked out my rail-to-rail op-amp? Look at the comments section on your comparator for the link.

jason9

7 years ago

Actually, there isn’t a link there. Just look through my circuits.

eekee

7 years ago

Not really, I've been working on a compact op-amp. (This one was a dead end in developing it, actually.) I got good results today, an 8-component op-amp with 2215x gain, and 11-component one with 250,000x gain. Both will go to one rail and get within about 1.5V of the other.

eekee

7 years ago

They're not very realistic, just meant for using in EC.

eekee

7 years ago

I'm going to look at yours and this one

eekee

7 years ago

http://everycircuit.com/circuit/6056482251472896

eekee

7 years ago

That one has some strange open-loop behaviour, presumably due to the capacitor.

jason9

7 years ago

What strange open loop behavior? Seems fine to me. The capacitor is to prevent oscillations.

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