how to make the ideal CMFB circuit?

[yikwon]

I want to know making the ideal CMFB circuit.

I saw that ideal CMFB circuit is made using netlist code in some books as below.

>> ecmfb vcmfb vss poly(4) vb1 o vcmref 0 vop 0 von 0 0 1 -1 0.5 0.5

Can I make the ideal CMFB using VCVS?

please answer about that.

 

[gingerjxb]

of course you can use vcvs to constitute the cmfb circuit
in fact, vcvs is represented by Exxx in spice

 

[yikwon]

I tried to make ideal CMFB circuit using VCVS but , it's not correct operation.
so, could you show me the ideal CMFB circuit?

 

[gingerjxb]

refer to this link:
h**p://kabuki.eecs.berkeley.edu/~keitho/ic771ca/pdf/cmfb.pdf
good luck

 

[yikwon]

thank you for your advidce.

I've already read that document. so, i tried to make ideal CMFB refering to the document you said. but, i had the strange results.

*pls, refer to attached file.

compared with opamp using real CMFB circuit, characteristics of the real CMFB is better. i don't understand...

what is my mistakes?

 

[gingerjxb]

is the output common-mode voltage of your amplifier 0.9V?

 

[yikwon]

yes, common mode voltage is 0.9V

because i use TSMC0.18 process.

that is wrong? i'm a beginner in analog circuit design. need your help.

 

[gingerjxb]

can you upload your circuit schematic?

 

[yikwon]

refer to attached file.

that is our opamp architecture.

The ideal CMFB circuit i made don't have any mistake?
if we use that kind of ideal CMFB circuit, the opamp with ideal CMFB have to work corretly. right?

thank you.

 

[gingerjxb]

your amplifier is a two-stage amplifier, so if your ideal cmfb circuit feeds the voltage to the gate of p-current mirror, your cmfb loop is a positive feedback loop. in order to make the amplifier work, change the polarity of cmfb amplifier vcvs

 

[yikwon]

thank you so much.

I solve the problems from your advice. thank you.

 

[graceice]

It's so good!