plot gain of a amolifier versus a bias voltage in hspice

[matin-kh]

plot gain of an amplifier versus a bias voltage in hspice

hi every one

I want to simulate an amplifier in hspice which the input of it is a differential amplifier and there is a dc voltage in my amp which i want to plot the gain by varying this dc voltage. i have two question:
1- because in the input there is a differntial amplifier so the input voltage of it should be like below:
Vin+ vin+ GND 1.5 10 1e4Hz 0
Vin- vin- GND 1.5 10 1e4Hz 180
a) a common voltage and sin voltage with opposite phase is it right?
b) which frequency should i choose?

2- what is the code for plotting gain of this amp versus dc voltage when the dc voltage is varying fore example between .5 v and 1 v?

with best regards
matin

 

[eahmadi]

Re: plot gain of an amplifier versus a bias voltage in hspice

Hi dear,
Firstly, as you mentioned in your request, you use differential amplifire so when you are simulating, you should apply common mode and differential voltage. common mode voltages should be same, however differential voltages must have 180 degree difference in phase. you should consider frequency response of your circuit to select optimal frequency.
secondly, I think It's not possible to have both DC and AC sweet at the same time,i.e you can't sweep DC voltage in order to investigate AC gain.I wonder!!!
Kindly regards,
Ebi:wink:

 

[erikl]

Re: plot gain of an amplifier versus a bias voltage in hspice

Vin+ vin+ GND 1.5 10 1e4Hz 0
Vin- vin- GND 1.5 10 1e4Hz 180
a) a common voltage and sin voltage with opposite phase is it right?

Yes, that's fine. Instead of 1.5(V), use a parameter (name of your choice, e.g. 'vbias' , including the apostrophes!)
Vin+ vin+ GND 'vbias' 10 1e4Hz 0
Vin- vin- GND 'vbias' 10 1e4Hz 180

It's possible that you have to declare this parameter - I don't remember:
.param vbias=1.5
The declaration value (1.5) is independent of your 'vbias' sweep values

Then you can sweep 'vbias'.

b) which frequency should i choose?

For the 'vbias' sweep, use the frequency of your interest.

I don't know if hspice can do multiple sweeps (as e.g. SPECTRE can). If so, the frequency in your Vin+, Vin- definitions doesn't matter, the sweep frequencies of your ac simulation are used instead.

2- what is the code for plotting gain of this amp versus dc voltage when the dc voltage is varying fore example between .5 v and 1 v?

Plot the gain versus 'vbias'.