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plot CMRR graph of OPA

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always@smart

always@smart

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graph for cmrr

Hi all,

can anyone here suggest me a test method that can plot the OPA's CMRR in frequency response?

thanks so much in advance

regards,
 

cmrr graph

What kind of simulator do you use? For Cadence you can run parametric AC analysis with common mode DC source at input.
 

graph cmrr versus frequency

There is a simulation technique for ploting CMRR vs. Freq. by SPICE in P. Allen's CMOS Analog Circtuit Design. You can look from that.
 

plot cmrr against frequency

You should necessarily make real voltage offset and mismatch of transistors of the input cascade, when will simulate the CMRR.
If it to not make, the result of simulation will be much better, than in silicon.
 

cmrr plot

hi ,
thanks for ur reply.

i'm using hspice and i still don get from ur answer that how can i actually configure the OPamp in order to ge the CMRR vs Freq?

hmm...maybe u can show me in netlist or a diagram.


thanks in advance.

regards
smart
 

you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR
 

devrimaksin said:
you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR
Click to expand...

--------------------------------------------------------------------------------------

but how can i configure the OPAmp to plot the CMRR vs Freq? Has anyone here done it b4, pls give me a suggestion.

thanks in advance.

regards,
 

always@smart said:
devrimaksin said:
you have to connect both input to the same AC source and run AC simulation
This will give you common mode voltage gain
then you have to simulate differential gain (regular AC simulation to extract small signal gain) and the ratio of these two will give you CMRR
Click to expand...

--------------------------------------------------------------------------------------

but how can i configure the OPAmp to plot the CMRR vs Freq? Has anyone here done it b4, pls give me a suggestion.

thanks in advance.

regards,
Click to expand...

Devrimaksin has told you how to do it. The key is to use 2 opamps, one for Avc the other for Avd.
 

hmmm, ok, i get it..i will try it. thanks for ur suggestion.

regards,
smart
 

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