jlee
Member level 2
Hi all,
I want to measure the transconductance gm of a PMOS common source circuit. I came up two methods, but they gave me very different results. I want to hear you guys' opinions to see which one is correct.
I want to plot gm versus Vgs of the circuit at the bottom.
Method 1:
Run DC sweep with Vgs from 0 to Vdd. Then choose Results> Direct Plot > main form> dc > transconductance:
Numerator terminal: I click on the one of Vdd supply terminals; Denominator Net: I click on the gate. This generates the plot on the left.
Method 2:
Run AC sweep with variable Vgs from 0 to Vdd, at very low frequency. I removed all capacitance parameters from the model. The when I plot, I choose Results > Direct Plot> main form > ac > current:
I click on one terminal of the Vdd supply. This generates the plot on the right.
I do this because I think the definition of gm is meaning the ac current signal on the source resulting from the ac voltage input on the gate.
Please let me know which method is the correct way to measure gm versus Vgs.
Thank you very much.
I want to measure the transconductance gm of a PMOS common source circuit. I came up two methods, but they gave me very different results. I want to hear you guys' opinions to see which one is correct.
I want to plot gm versus Vgs of the circuit at the bottom.
Method 1:
Run DC sweep with Vgs from 0 to Vdd. Then choose Results> Direct Plot > main form> dc > transconductance:
Numerator terminal: I click on the one of Vdd supply terminals; Denominator Net: I click on the gate. This generates the plot on the left.
Method 2:
Run AC sweep with variable Vgs from 0 to Vdd, at very low frequency. I removed all capacitance parameters from the model. The when I plot, I choose Results > Direct Plot> main form > ac > current:
I click on one terminal of the Vdd supply. This generates the plot on the right.
I do this because I think the definition of gm is meaning the ac current signal on the source resulting from the ac voltage input on the gate.
Please let me know which method is the correct way to measure gm versus Vgs.
Thank you very much.