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Design >> Analog Design >> supply & ground PSRR in opamps
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Message started by rajeee1000 on Jul 2^nd, 2007, 9:19pm

Title: supply & ground PSRR in opamps
Post by rajeee1000 on Jul 2^nd, 2007, 9:19pm

Hello members,

Does anyone know/have a good resource talking about supply and ground PSRR in various different architectures of the operational amplifiers extensively alongwith the concerned tradeoffs involved in the design.

Thanks in advance,

Regards
Rajesh

Title: Re: supply & ground PSRR in opamps
Post by Visjnoe on Jul 3^rd, 2007, 12:08am

Dear,

I don't know of any source where the PSRR topic is covered extensively. Perhaps the book by Laker and Sansen is the best reference: in the chapter on the Miller OTA it has a fairly extensive investigation of the PSRR
(both from VDD and VSS), supported by handcalculations.

Once you understand these, I think you can easily extend this method towards other amplifier topologies.

Regards

Peter

Title: Re: supply & ground PSRR in opamps
Post by vivkr on Jul 10^th, 2007, 3:56am

Hi Rajesh,

It would be quite hard to find a paper on this subject. There was a paper by Sansen and others in JSSC titled "CMRR and PSRR of ..." but I
don't have the exact link to it. Perhaps you can try searching on IEEE Xplore for JSSC papers by Sansen. It is a brief paper.

Some information may be found in the JSSC paper by B K Ahuja "An improved frequency compensation technique ...", Dec. 1983.

I assume you are talking of fully differential amps. Basically, you can improve PSRR by increasing the impedance between the supplies
and the output => more impedance => swing reduction or need for more gain. This is typically the standard tradeoff, and also holds well
for cascoding.

If a differential amplifier is designed in such a manner
that any excitation from the supply shows up as an identical disturbance on both halves of the differential path (magnitude and phase), then
you have a high PSRR. So, you need excellent matching.

Also, in single-ended amps, there are other effects at work. These suffer from inherent asymmetries that reduce PSRR. For instance, in
a current mirror, VGS is the same for both halves, but VDS not, and this will cause reduction in PSRR. In a 2-stage amp, you have poor PSRR
beyond the unity-gain bandwidth (see Ahuja paper).

Regards
Vivek