Total Gm of OTA versus Frequency

[an_82]

How can I plot the total Gm of OTA circuit versus Frequency in HSPICE?

 

[erikl]

Run an ac analysis with an ac unit (1V) input voltage, then plot output-current vs. frequency. Output-current in [A] corresponds to Gm in . Or use 1mV input voltage and get [mS] of Gm.

 

[an_82]

Dear erikl,

I understood what you mean, but I could not get the desired output.

I have two questions:

1. My circuit input is differential and the output is sigle-ended. How do I apply the input? I applied "ac=1 sin(0 1 1meg)" as the input voltage (in open-loop config.).
2. I putted a capacitor at the output. Am I right?

Thanks.

 

[erikl]

1. This is correct, but works only if your inputs are DC biased to a working operation point (i.e. within the ICMR).
2. This doesn't matter if you measure the output current. It just could decrease the output voltage bandwidth because of slew rate limitation.