Hi all,

i'm trying to run a stability analysis on a current output passive mixer which is essentially a passive mixer followed by a trans-impedance amplifier. I first tried modelling the output impedance of the switching stage (the passive mixer) as a resistance, and then ran the normal stability analysis to find the loop gain. Here i found no problems. I used a cmdmprobe to break the loop. However, when I ran the pstb analysis with the LO signal turned on, the DC loop gain dropped from 70 dB down to -30 dB. Has anybody else encountered a problem like this? The PSS and Pnoise analysis give reasonable results.


thanks,
Aaron

Hi,

thanks for the reply.

Quote:


I'll try PAC tomorrow. thanks

Quote:


I'm using an op-amp based TIA, so I inserted the probe at the input of the opamp (connected to the gate of the input transistor).

I expected there to be some difference between stb and pstb analysis, but obviously not that much. BTW in order for PAC analysis to run correctly, I had to change the parameter "version" in the BSIM model file from "version=3.3" to "version=3.2". Could the problem have something to do with that?


thanks,
Aaron

Hi Andrew,

Quote:


the log file says i'm using version 6.2.1.145  from Jan 10, 2008. I'll see if I can update it...

thanks,
Aaron

ok it seems that i wasn't using the model with version=3.2, but the one with version=3.3. Now that i've changed it to version=3.2 it works. I guess i'll try updating the spectre version later when i have more time.

thanks,
Aaron

Thanks a lot! I guess i'll see if I can update MMSIM sooner than I thought,

thanks,
Aaron