[SOLVED] How to determine the size of transistor in cmfb for folded cascode

[paramis]

Hi all,
I want to design a CMFB for fully differential pmos-folded cascode.
I use this circuit,but I don't know how determine size of transistor?
output diff swing:2v p-p

 

[erikl]

Re: cmfb for folded cascode

View attachment 79493... I don't know how determine size of transistor?

Depends on

• Process
• Supply voltage
• Bandwidth (UGB)
• ... resp. permitted power consumption

 

[paramis]

Re: cmfb for folded cascode

0.35um process
supply:3.3
UGB:1.5gig
total power consumption:25m

 

[erikl]

Re: cmfb for folded cascode

Recommendation for starting:

• For mc11, mc21, mc12, mc22 I'd use L=1µm and W/L = 50 .. 80
• For the rest (mc(0)[12356]) I'd use W/L = 2µm/4µm
• For UGB=1.5GHz use a current 100µA..1mA (via Vctrl)

Simulate!

 

[paramis]

Re: cmfb for folded cascode

Hi erikl,
tnx for your help.
I simulated but it did not correct work.all of mc11, mc21, mc12, mc22 are off.
can you explain how did you determine that size?
I forgot output common mode=vdd/2.

 

[erikl]

Re: cmfb for folded cascode

Hi paramis,

which current did you use? Where did you inject it? Vctrl? What are the Vth's of your MOSFETs?