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Question about AC simulation with verilog-A model

dskang

Hello,

I have a question of AC simulation. Thank you in advance for your help.

I'm using verilog-A based device model, and I tried to measure gm of the devices.

So the two method I did was : 

1) I measured Id-Vgs curve (DC sweep)and measured slope at certain bias point.

2) I did AC simulation and measured current gain at drain side.

However, the two simulation results were quite different, 1) showed about 460u, while 2) showed about 350u.

As I'm trying to use AC gain, I need to make AC gain result match with DC slope. (I saw regular pdk devices make similar result in two simulations)

As far as I know AC simulation makes some linearization of the model, so what I'm guessing is that there may be some options can be changed to make linearization more precise. (If not considering changing the model)

Could you tell me what I can do, or what can be the problem?

Regards,

Dongsuk Kang

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