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Design >> Analog Design >> KT/C noise in switch cap circuits
https://designers-guide.org/forum/YaBB.pl?num=1341231313

Message started by raja.cedt on Jul 2^nd, 2012, 5:15am

Title: KT/C noise in switch cap circuits
Post by raja.cedt on Jul 2^nd, 2012, 5:15am

hello all,
in a normal sample and hold circuit, during sampling phase integrated noise every one says Kt/C, this every one derives by assuming switch as a resister, but my doubt is we have use mosfet noise in triode we get KT*gamma/C. Is this correct?? or where i am going wrong?

Thanks,
Raj.

Title: Re: KT/C noise in switch cap circuits
Post by carlgrace on Jul 11^th, 2012, 6:10pm

When you derive kT/C noise in this way the resistance of the switch cancels out. So it doesn't matter what the resistance is. If the effective noise resistor is a bit bigger, the RC circuits bandwidth will be a bit smaller and vice versa, so you're still stuck with kT/C.

Title: Re: KT/C noise in switch cap circuits
Post by mixed_signal on Jul 22^nd, 2012, 12:53am

When u tell vn2=4kt*gamma/Ron then effective thermal resistance is gamma/Ron. So, due to pole formed by this resistance, gamma gets cancelled out.

Title: Re: KT/C noise in switch cap circuits
Post by mixed_signal on Jul 22^nd, 2012, 1:57am

sorry Ron/gamma :)