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Effect of input voltage on gate capacitance of a MOSFET

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jiveshgovil

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My query is that what is the effect of input voltage on gate capacitance of a MOSFET?
 

I think gate capacitance not depend on gate voltage,
both of Gate to Drain, and Gate to Source are fixed.
But because of miller effect cpacitor of GD can be appear very greater than initial value.

Regards,
Davood.
 
Davood Amerion said:
I think gate capacitance not depend on gate voltage,
both of Gate to Drain, and Gate to Source are fixed.
But because of miller effect cpacitor of GD can be appear very greater than initial value.

Regards,
Davood.
Click to expand...
The gate capacitance is a huge function of gate voltage. See **broken link removed**.
 
The mos gate capacitance changes with the gate voltage, that's why we can use it as a varactor in LC oscillator
 
In MOSCAP, gate capacitance is a function of gate voltage bias Vgs.

Even in CMOS transistor, gate capacitance is also depending on Vgs. Because total gate capacitance is composed of overlap capacitance with drain/source, and channel capacitance. Overlap capacitance is constant, but channel capacitance is depending on the operation mode. For example, in saturation mode, channel capacitance is (2/3)*W*L*Cox; in linear mode, channel capacitance is W*L*Cox.
 
take a look at this site:

Code: 
http://jas.eng.buffalo.edu/

it contains simulations of applied gate voltage on various behaviors of MOS structure.. and many more

cheers
 
Input capacitance is pretty much constant but the output and the reverse capacitance do vary more with voltage. Take a look at any data sheet for a power MOSFET and you should see the curves of capacitance versus voltage.

For example, take a look at the figure on page 4 lower right hand side
**broken link removed**

Note the following definitions

Input capacitance Ciss = Cgs + Cgd
Output capacitance Coss = Cds + Cgd
Reverse capacitance Crss = Cgd

Best regards,
v_c
 

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