Does anyone have a VI to measure capacitance of a mosfet

[jimmydharia]

I am new to Labview and i am currently designing a circuit to measure the voltage, temperature and current  changes in LAbview . But I am having difficulties on measuring the capacitance Does anyone have a tutorial or a VA can Does help me to measure temperature of a mosfet.

any help would be really appreciated

[BrentSchenk]

do you have an instrument that will be measuring the temperature of the mosfet?

[jimmydharia]

thanks for the reply .as of now I m using a virtual instrument that i have simulated using the MAX .  so no i dont have a instrument right now

[smercurio_fc]

It's not clear which part you need help with. Are you seeking help in selecting the instrument, or are you seeking help in programming (i.e., collecting data using DAQmx), or are you seeking help in the technique?

And I hope it's not "all of the above". 

[jimmydharia]

nope not all of above for sure .... welll here this is my problem.. i made a mosfet VI which displays the IDS VGS AND VGS of the mosfet now i also wanna calculate the value of the capacitance of the mosfet

now i know the formula of the capacitance C= 1/2wlcox (or something ) might work but i jsut wanna know a better way of doing it ......

so i was basically seeking a circuit that could measure the capacitance jsut an example or something soo that i can with the aid of that example make modify my circuit for capcitance measurement

[BrentSchenk]

Wow,  you are kind of in the wrong forum here as we arent all electrical engineers (but i am and embarassed to say that i dont know on the fly how to measure the capcitance of the mosfet, or if it can even be done easily, but now you have me curious so ill take a look but dont expect too much around here as thats more of a EE type question).

also there are a few small signal capacitances youc ould be measuring.  is this what you are talking about because there are different models as well.  I forget it, as i havent taken a circuits class in months but there has to be Cds, Cgs, and Cdg right?

Message Edited by BrentSchenk on 04-07-2009 02:26 PM

[BrentSchenk]

oh and fyi if you type "measure capacitance of a mosfet" into google this post is already the first to come up, cant be asked too often then

[jimmydharia]

thanks for ur help 

well as of now i m neglecting the small signal capacitances just to make my formula smaller and simplier 🙂

[johnsold]

The gate capacitance of a MOSFET varies in complicated ways while the device is turning on or off.  You can measure gate voltage and current and calculate the charge and then infer the capacitance from that or use a small high frequency ac signal superimposed on DC gate drive to try to measure the small signal capacitance dynamically.  For any of these measurements you may need to use care to avoid having the measurement circuit modify the behavior of the device you are measuring. 

The formula you mentioned above seems to be based on the device geometry and is not related to external electrical measurements.

As several others have asked, please tell us specifically what you are trying to measure, under what conditions, and what will be the use of the results.

Lynn

Some of us are EEs.