Miller OTA

[danmicro]

Hi,

I am designing a 2-stage miller OTA. I am stuck at 51dB gain with PM 80. I need at least 60dB. How can I reach 60 dB. I'm using gpdk045 in cadence.

 

[dick_freebird]

By "Miller OTA" I guess you mean basic Miller feedback
for frequency compensation?

Your 51dB is DC gain? That doesn't care about the
capacitor.

gm peak and Rout is all you've got. Which can be
improved by OP adjustment (or geom leading to,
to a point)?

If answer is "none" then it's on to toplogy, but seems
you're committed to that.

I've seen craptastic op amps in lower nodes. You
don't mention voltage or bandwidth. Have you
looked at the I/O devices for a better common
mode range (and more headroom, available for
saturated operation, I know you kids love to chase
that with the "methodology" they like to teach)?

gpdk is of course a hoax and no telling how real
or realistic any of it is. Still you might benefit by
better understanding the transistors, where you
will find best gm and best Rout and hopefully,
together - but faint hope, that, as roles and positions
will differ because they must. So then you have to
choose smartly, which you need where in what
proportion and how to get.