biasing and cmfb circuits

[_SquiD_]

common mode feedback circuit

Who can help me with an biasing circuit and a cmfb circuit for the attached LNA ?



_Squ!D_

 

[arunkumar446]

at what frequencies you are going to operate this circuit?

 

[_SquiD_]

I have to make a sampling circuit using such LNA's .... the frequency will be aprox. 100KHz.

 

[arunkumar446]

then you are going to use it in Switched mode. Then you can use SC-CMFB, which is better in performance compared to other CMFB's.
You can refet to this paper Analysis of Switched-Capacitor common-mode feedback circuit by choksi, carley

 

[_SquiD_]

Thanks, arunkumar446 for the paper. I found this CMFB version in Gray's book. But not with an analysis; the paper seems quite useful. Does anyone have any other papers with other CMFB analysis ?

_SquiD_

 

[arunkumar446]

dual phase SC-CMFB is described in this paper

 

[arunkumar446]

this paper has a ota + SC-CMFB it has classic sentences

 

[arunkumar446]

this paper has a little info.

 

[_SquiD_]

Can anyone tell me what influences the value of the compensation capacitor ? How should it be in my LNA ? Can anybody give some advice?


_SquiD_

 

[arunkumar446]

do you mean frequency compensation capacitor or some thing else related to SC_CMFB.

 

[_SquiD_]

do you mean frequency compensation capacitor or some thing else related to SC_CMFB.

I was reffering to Cc of the LNA amplifier shown in the first figure of this topic.

_SquiD_

 

[arunkumar446]

You are usign ribner compensation technique, in general it is said that compensating by this method is quite difficult, The original paper by Ribner is "Design techniques for cascode CMOS opamps with improved PSRR and common mode input range". in general we try to decrease the capacitance by merging cascode devices S and D, as in this technique we are connecting a capacitor so we have to have a contact which increases capacitance.

In this paper with simple mos model, transfer function shows it is a 3rd order. so it makes life difficult with this technique to design. but it's a very clever technique.

Added after 1 minutes:

The paper which i mentioned does the work for designing. Hope this helps.

 

[_SquiD_]

You are usign ribner compensation technique, in general it is said that compensating by this method is quite difficult, The original paper by Ribner is "Design techniques for cascode CMOS opamps with improved PSRR and common mode input range". in general we try to decrease the capacitance by merging cascode devices S and D, as in this technique we are connecting a capacitor so we have to have a contact which increases capacitance.

In this paper with simple mos model, transfer function shows it is a 3rd order. so it makes life difficult with this technique to design. but it's a very clever technique.

Added after 1 minutes:

The paper which i mentioned does the work for designing. Hope this helps.

Are you willing to share this paper with us ?

_Squ!D_

Added after 7 minutes:

The thing is that I'm kinda of blocked. I don't know what to do with this LNA ... I found it in holberg and allen ... and it is beyond me. I can't understand how big the currents should really be all around this circuit, the sizing of the transistors, the analysis of this amp and effectively the low noise functionality of this LNA. I have to admit that I'm more a novice in analogic design but I'm so willing to learn.

 

[philharmonic]

learning