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Design >> Analog Design >> unity buffer gain
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Message started by studentmember on Oct 9^th, 2009, 2:35pm

Title: unity buffer gain
Post by studentmember on Oct 9^th, 2009, 2:35pm

hi! i have to design a unity buffer gain with a CMOS differential pair with current mirror as active load...how can i start to design it?...i'm inexpert student..and i don't find books that can help me...thanks

Title: Re: unity buffer gain
Post by Mayank on Oct 9^th, 2009, 2:46pm

Hi student,
There's a pretty straight-forward way to design a opamp for unity buffer config. Opamp design is simple, you can choose any topology - differential/single-ended / 1stage/2stage OTA design.
Two important things to keep in mind while designing unity gain buffers are :-
1. ICMR and OCMR should overlap & should satisy your signal swing specs.
2. Output CM level & I/p CM level should match / kept in mind while designing.

Fully Differential topology will allow you to place a good CMFB ckt to control output/input CM level.

Design of OTA is basic and you can use gm/id methodology for it.

Pls lemme know if you hv any further queries.

regards,
Mayank.

Title: Re: unity buffer gain
Post by Mayank on Oct 9^th, 2009, 2:50pm

Also i would suggest you to go through chapter 9 on Opamp Design of 'Design and Analysis of CMOS Analog Integrated Circuits' by Behzad Razavi.

It contains a good enough anaylsis to start opamp design. Rest you can learn in the process of doing it.

-- Mayank.