How much space you got to waste?
I think you need to give a much more specific question, way too  vague

first design open loop amplifier with specified dc gain. So you would get gm1 and gm2. Generally you have load cap spec from there your second pole would be gm2/cl, for 60 deg PM at least place UGB 4 times below 2nd pole. so now you wil get ugb and that is gm1/cc.

you can refer razaavi for this.
for all feedback and op amp compensations better follow this site.

http://www.ee.iitm.ac.in/~nagendra/videolectures/doku.php?do=login&id=200901vlsi...

vineeth wrote on Jun 7^th, 2011, 9:03pm:


what a terrible waste of area! I would suggest that you go over the basics of miller compensation once so as to better understand how pole splitting works. as you do not mention either power consumption or noise as a reason, I suppose that those are not critical.

with that out of the way, the general rule is that the compensation cap is NEVER made larger than the output load cap in a good design. you have got gm1, gm2, Cc and Cl. Usually, Cl will be fixed by the application. And gm1 is tied to Cc. So you still have two parameters to play with: gm2 and Cc. Use both! Usually, gm2 is about 4x-5x larger than gm1 for decent phase margin. With that, you will also get a decent value for Cc. And don't forget to nullify that RHP zero using one of the various methods available for that purpose...

Vivek

100pf is a ton of real estate inside a chip, that probably needs to be reduced in size.

Funny thing - I have not used pole splitting in many years.

I use a source follower to drive the feedback capacitor, which provides feedback while getting rid of the HF feedforward path. (No resistor anymore in the feedback path that way)

Also, for best swing, outputs are OTA, class AB, so that you can get rail to rail output.

Just my approach, others are viable, but the above has served well for me.

i dnt have a load cap specification..but my high gain opamp has a ugb spec of 10mhz and a Imax of 500u...my rhp zero is taken care of and so is the phase margin..bt to reduce ma ugb and hence to push ma dominant pole inside i need to increase ma miller cap..i mt able to keep ma ugb within 10Mhz only with a miller cap minimum of 80pf

vineeth wrote on Jun 11^th, 2011, 5:59am:

Vineeth - you can also reduce ugbw by reducing the gm of the input diff pair by using less current or more Vgs-Vt. 100pF is huge -- I've only needed something like that to lower the ugb to much less than 100kHz to get total noise down. Why do you need such high tail current?

You are going to have very low slew rate. On the other hand it does not necessarily waste area since mim caps can be placed over active circuitry which would otherwise be unused. Still, it is large compared to most designs.

Vivek - I believe LE's method isn't Ahuja. With Ahuja the feedback path is output -> Ccomp-> source of common gate amp ->  gate of output device. With LE method the path is output -> gate of source follower -> Ccomp -> gate of output device.

[quote author=RobG link=1307475244/0#11 date=1307977438]vineeth wrote on Jun 11^th, 2011, 5:59am:


Rob,

Thanks for pointing out the error. Indeed, the use of a source follower to turn the bidirectional miller coupling cap into a unidirectional (to first order) feedback network would not be the same as the Ahuja method.

The source follower method would also not give rail-rail output swing, although the Ahuja method might work there still. Your comments Jerry?

Vivek