Plotting gain vs. VinCM

[EmbdASIC]

Hi all.

i want to plot Adm (differential gain) vs. VinCM (Input common mode level) in spectre. I will probably sweep the DC, but was a bit confused how it will plot gain vs. dc swept parameter ?

 

[sjamil02]

I think you can plot the gain using calculator.

x-axis will be your dc sweep voltage. y-axis is your gain Adm. To plot this go to tool > calculator and plot Adm=gm*rout.

sj

 

[EmbdASIC]

My gain is an expression for a four stage OTA gain, which i want to sweep with my input Common mode level. I guess there is little clue to what-to-do in your reply !

 

[erikl]

Hi all.

i want to plot Adm (differential gain) vs. VinCM (Input common mode level) in spectre. I will probably sweep the DC, but was a bit confused how it will plot gain vs. dc swept parameter ?

Use a closed dc and open ac feedback (iprobe from C@dence lib, or big L / big C feedback). Then run an ac analysis with swept dc (VinCM, as you suggest) at the pos. input, and a VinDM ac sinus source with a frequency of your interest in series with your dc feedback, then plot Vout/VinDM(ac) against VinCM.

 

[EmbdASIC]

Hi thanks for your input.
Rest is fine, the only problem i have is plotting Adm vs. swept DC on the same plot in spectre. Usually it does not plot AC and DC results in the same plot.


Regards,
EA