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Simulators >> Circuit Simulators >> How to plot gain vs. Vout of an amplifier
https://designers-guide.org/forum/YaBB.pl?num=1141904026

Message started by mimic on Mar 9^th, 2006, 3:33am

Title: How to plot gain vs. Vout of an amplifier
Post by mimic on Mar 9^th, 2006, 3:33am

Hi,

is there a way of plotting gain vs. output-voltage curve of an amplifier ? The problem I am solving is how to make a sort of test-bench for single stage amplifiers that would show the gain/voltage-swing tradeoff when tweaking such amplifier .. to clearly show the effect of the cascode transistors etc. I am talking about amplifier stages with single-ended input and output. The simulator I use is eldo.

I'll appreciate any hints on this. thanks
MM

Title: Re: How to plot gain vs. Vout of an amplifier
Post by aamar on Mar 9^th, 2006, 5:59am

Hello,

I think what you need to do is called pareto diagram, which shows the tradeoff between different performance parameters.

but first let us discuss the testbench which should be used

1. you should fix the frequency you are going to use in simulation.

2. Set transient analysis using an input sinsoidal wave source and the frequency you defined.

3. This transient simulation should run several times using parametric analysis in which you sweep an optimization parameter, which may be the size of the cascoded transistors as I understood or anything else.

4. Plot the output then you will have what is called a family (group of waves)

5. If you are using cadence then use the calculator and the special functions to define the gain and the swing, and plot them versus the optimization parameter.

6. You will have two waves, one representing the gain and the other representing the swing.

7. Plot them against each other, I am not sure if the calculator can do it or not and this should be the Pareto diagram.

8. Another solution, I think you can define a weight function ( W(gain,swing)= A*gain + B*swing ) which is the sum of the both gain and swing with adjusting a weight for each of them and try to optimize this function to what you need.

I hope this would be helpful.

amar

Title: Re: How to plot gain vs. Vout of an amplifier
Post by Ken Kundert on Mar 9^th, 2006, 10:12am

Another possible approach if you are using Spectre is to simply perform an AC analysis to compute the gain while sweeping the DC input voltage to drive the output over it intended range. In this case the frequency would be fixed.

-Ken