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Why is the capacitance between gate and drain is almost zero after pinch off?

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iVenky

iVenky

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Initially we have oxide capacitance between gate and body. But once we have the channel the capacitance gets distributed between source and drain. I just could get this "distribution" thing - Does that mean that there are some static negative charges in source and drain? Also after pinch off there is no capacitance between gate and drain. Why is that so?

Thanks in advance.
 

iVenky said:
Initially we have oxide capacitance between gate and body. But once we have the channel the capacitance gets distributed between source and drain. I just could get this "distribution" thing - Does that mean that there are some static negative charges in source and drain? Also after pinch off there is no capacitance between gate and drain. Why is that so?

Thanks in advance.
Click to expand...

Hi friend.........

I think the current Igs is zero, so there is no capacitance between drain and gate.
 

The channel is what connects gate plate capacitance to the drain
(and source). When the channel goes away only the overlap &
fringing capacitance is "hooked up", the rest is returned to body
instead of the inversion sheet when not inverted.
 

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