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

Help me with analyzing this opa?

Status
Not open for further replies.
wjxcom

wjxcom

Full Member level 5
Joined
Sep 7, 2005
Messages
281
Helped
4
Reputation
8
Reaction score
3
Trophy points
1,298
Activity points
3,840
How to analyse this opa?

Hi, all: please look at this opa, I have three questions:

1. I do not know what is the role of the transistors M14--M19: why to use these transistors?

2. this circuit should be compensated, so I think the capacitances C3 and C4 should be connected with the output of the first stage and the output of the second stage. But in this circuit, can these two capacitances compensate thie circuit? At the same time, why not use a capacitance to take place the capacitances C3 and C4?

3. what is the role of capacitance C2?

I am a fresh man to design analog circuit, I think I can get answers from this forum.

thax!!!
 

Re: How to analyse this opa?

I'd love to help you but I think you forgot to include the picture of the schematic!
 

How to analyse this opa?

1. M14-19 are used to adaptively bias Pload.
2. u can use one cap to replace c3and c4.
3. c2 is used to compensate amp. This method is proved to be more efficient.
 

How to analyse this opa?

Hi, swicap: can you explain detailed? what's the mean of "Pload"? why C2 can be used as compensate capacitance? and what is the role of C3 and C4?
 

Re: How to analyse this opa?

Here are my findings:

1) M14~M19 are common-mode feedback for the first-stage of this two-stage amplifier. The second-stage of this OTA already has a global CMFB from 'Vcmfb' input pin, so the first-stage CMFB is a local loop. You need to pay some attention to this local loop stability though because I don't see compensation cap for this loop.

2) C0 to C3 are cascode-miller compensation capacitors for this two-stage compensation. Compared with conventional Miller compensation, this Ajhua compensation is more effective because it can use smaller capacitor to achieve the same pole-splitting effect.

Give me some credit if I address your problem properly.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top