I mentioned it as reactance as a general case but I know it is mostly capacitance. How do I find input/output capacitance of a gain stage/MOSFET/Network?. Usually it is the imaginary part of the total input/output impedance. So If I do SP simulation and plot the imaginary part of ZP from direct plot, It will give me the input/output capacitance of a gain stage. Correct? But why do some people use YP from direct plot for this purpose. I just want to know which parameter to use (Say ZP) and what modifications I should make if I use the other parameters(Say YP).
P.S I know if the network has series connection it is easier to use Z parameters and If it is parallel connections it is easier to use Y parameters. But If we consider the network as a block box we wouldn't know how the connections are inside.
I mentioned it as reactance as a general case but I know it is mostly capacitance. How do I find input/output capacitance of a gain stage/MOSFET/Network?. Usually it is the imaginary part of the total input/output impedance. So If I do SP simulation and plot the imaginary part of ZP from direct plot
No.. If you are interested in the input impedance, look at ZM1 and for output impedance, look at ZM2. Not Z parameters. V1 = Z11*I1 + Z12*I2. If you only look at Z11, then you don't see the effect of Z12 which is the effect of the feedforward capacitance (aka Cgd). ZM1 captures both of them.
In my eyes the miller effect makes the system unlinear, you see this in the voltage plateau of V_gs.
Thus you can't apply S parameters.
You need to input power to get the gate charged. ... but you don't get the whole power back, because all the power for the miller effect is dissipated within the Mosfet.
It is a lossy unlinear system, depending on V_DS...and can't be simulated with an R C circuit.
No.. If you are interested in the input impedance, look at ZM1 and for output impedance, look at ZM2. Not Z parameters. V1 = Z11*I1 + Z12*I2. If you only look at Z11, then you don't see the effect of Z12 which is the effect of the feedforward capacitance (aka Cgd). ZM1 captures both of them.
Yeah sure.
I used this
1.CinfromY=(1 / (abs(imag((1 / ypm('sp 1 1)))) * 6.28 * xval(ypm('sp 1 1))))
2.Cin=(abs(imag(zm(1 ?result "sp"))) / (2 * 3.14 * xval(zm(1 ?result "sp"))))
There is a lot of difference between two of the results and using 2. the Cin value is not constant over the frequency range. That is the my confusion as to which one to use and the Cgd effect would so much ?
Yeah sure.
I used this
1.CinfromY=(1 / (abs(imag((1 / ypm('sp 1 1)))) * 6.28 * xval(ypm('sp 1 1))))
2.Cin=(abs(imag(zm(1 ?result "sp"))) / (2 * 3.14 * xval(zm(1 ?result "sp"))))
There is a lot of difference between two of the results and using 2. the Cin value is not constant over the frequency range. That is the my confusion as to which one to use and the Cgd effect would so much ?
Yes.. I see your point. I understand my mistake. Y11 = jw(Cgs+Cgd) (because the output would be shorted and both capacitances would come in parallel). Z11 expression will be longer but it will include the effect of Cgd. I apologize for misleading.