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OpAmp design - from theory to practice

Thanks JM for posting it before me!

I was not directly involved with the project, but from the notes I found ar ound it seems that the main "problems" they had with the first version (the one in the article) were:

- too much leakage (degrading the low current measurements)

- the need of an FPGA to operate the chip (to control it and readout the da ta)

- some linearity issues

I don't know if I can really say I want to "improve" it. The chip itself wa s working quite nice, but for several reasons (I can explain, but it would take a long post and it is not super-relevant to the discussion here) we ne ed a new version with a new technology.

Now, I can keep the same approach (no problem on my side) but changing tech nology node means doing a redesign and re-dimension of the OTA, for starter s. And this is where I struggle, because I am a bit in the dark about how t o "obtain" the specs of the amplifier.

But I think I might be starting from the wrong point (after reading the pos ts here): I probably should start with the OpAmp as a black box and conside r it ideal, and from there calculate the behavior of the circuit in ideal c onditions; and after this, probably the OpAmp becomes a bit more straightfo rward.

Thanks for all the info. I have some reading to do!

Francesco

Reply to
Francesco Zappon
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around it seems that the main "problems" they had with the first version (t he one in the article) were:

data)

was working quite nice, but for several reasons (I can explain, but it woul d take a long post and it is not super-relevant to the discussion here) we need a new version with a new technology.

chnology node means doing a redesign and re-dimension of the OTA, for start ers. And this is where I struggle, because I am a bit in the dark about how to "obtain" the specs of the amplifier.

osts here): I probably should start with the OpAmp as a black box and consi der it ideal, and from there calculate the behavior of the circuit in ideal conditions; and after this, probably the OpAmp becomes a bit more straight forward.

Hmm, I guess a lot depends on where the problems are. Are the caps in the silicon? (could they be external?)

Radiation damage seems like it would cause leakage everywhere.. (~proportional to area.)

George H.

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Reply to
George Herold

Can't find the P/N RHFL4913 but yes, of course you need sufficient output caps in such an application.

Then with many LDOs there is often inadequate stability and those I would never use in hi-rel.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Maybe you should then look into SOI like Phil suggested. Then guard rings and all the usual low-current tricks.

Linearity will always be tough because of your 120dB. FPGA could be done in space. Work together with Gerhard maybe? He is located close to you and is self-employed as far as I know.

If it is more or less a transfer from an obsolete technology to a new one for foundry reasons and such I'd talk to an analog IC design house.

I can't imagine going to another node being a large obstacle. You can always use larger geometries as you did before, it's just the minimum that is now lower. Plus of course process differences but that is where a good IC design house helps. We always used those for IC designs, never went it alone.

Just keep in mind that in the real world nothing is ideal and you will always have offset, offset drift, offset tempco and such effects.

It sure is a nice engineering challenge. Those are the things that keep us young :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I'm right here. Francesco and I are even in the same beam instrumentation group (although I've never met him, I think). I have my own little problems at the moment. We're about to start up the accelerators and I have lots of work that can't wait.

Jeroen Belleman

Reply to
Jeroen Belleman

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