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# Questions about large signal model,gm and C-V?

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#### pursue

##### Newbie level 5
cv model

Hi, all! i want to get the c-v curves about the GaAs HEMT,but i don't know the measurement environment,also is it at the high freq,the low freq or sth else,i just know the C-V have sth about the Vgs and Vgd etc,plz give some advices or some reading materials.
was the gm modeled in small signal or large signal model, and why the gm is different from DC-IV curve and high freq conditions,may be its the dispersion frequency,some papers model the phenomena with a sub circuit at the output in the drain source,and i have read some papers about that ,but i just don't know how to improved this.
how to implement the C-V model in the large signal model,i just write the equations about the I-V and C-V in the ADS equations, and the topology is just the same as the traditional one,but the S para is different from the small sigal model, this is the disconsistent between the small signal and the large signal model,then how to make the I-V and C-V together to get the large signal model.is the small signal characteristics can be gain from the large signal model? or the small signal model just can get the small signal like gain, S para etc,and the large signal can get the Pout,PAE,IMD etc.is there existed a large signal model not only can reflect the small signal conditions,but also characterize the large signal conditions.
plz give you understanding about the small signal and large signal model, i am confused about the model about the GaAs HEMT large siganl modeling all from the measurement data.

thanks all!
pursue

what is large signal

you just need to fit the I-V and C-V curves,then all the other parasitic parameters are extracted from the small signal model,then you have to setup a subcircuit , maybe all the performances like S_para,gain,p_1dB,etc can be gotten,it's just what i can tell you,maybe others can give some more useful adivces.

Points: 2