Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

CMFB Loop and stability

Status
Not open for further replies.
A

asuprash

Newbie level 6
Joined
Dec 6, 2006
Messages
11
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,371
Hi
In a CMFB employing a DDA, how do we provide compensation.
In the Baker L Boyce Book he discusses that capacitors at the input
of the CMFB amplfifer can be used for Differential compensation as
well as for CMFB compensation.

If we increase the capaciatance at the leads of a diff amp, then we would
get compensation (increase of stability) due to the dominant pole having roll
-off much earlier.
However, these load compensation caps from an Diff-amplifer act as
input caps to the CMFB amplifier.

How can these input caps provide compensation ?
Is there some Miller effect I am missing ?

Regards Prashanth
 

note that what u need to compensate is the CMFB loop not the CMFB amplifier and as u say by increasing the load capacitance u push the dominant pole to roll-off earlier and the dominant pole of the differential amplifier is at the same time the dominant pole of the CMFB loop(assuming that the mirror pole introduced by the DDA is much larger than that dominant pole) and thus by this way u compensate both the differential amplifier and the CMFB loop
 

Hi Thanks,
I realised that. Whenever you compensate you compensate the whole loop,
and it doesnt matter where exactly you put those capacitances as long as the dominant pole exists there.

Regards Prashanth
 

I suggest you to read carefully final chapter of Gray & Hurst's book, where they discussed about different CMFB configs. as well as CMFB loops and their compensation techqniues.
Also to measure CMFB loop specs. you may use their references.

Regards,
SAZ
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top