[SOLVED] Graph results of common source amplifier.

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MagnumX

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Hello, guys. I'm wondering is it the value of resistance R1 and R4 won't affect the output voltage of amplifier ? For original design, R1 and R4 resistance is 1K respectively. For 2nd design, i have changed their value to 500. After that, I have compared the output voltage between them. I found that there is no different between them. Why? Can anyone provide some opinions ? Thank you . Your help is greatly appreciate.

Ps: Attached here is the design circuits and the results of each design.
Ps: I'm using Mentor Graphic to design these circuits.
 

The resistors have no effect because V3 drives a voltage to the gate node. V3 is also shorting any input signals.

Biasing the gate with a fixed DC voltage is a bad design anyway if you want a linear amplifier.
 
Thank you so much, sir. It helps me a lot. I will try to improve this design. By the way, can i know is it possible to find out the value of small-signal output resistor, ro and transconductance, gm based on this design circuit ? Got any formula can calculate it ?
 

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