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Design >> Analog Design >> Slew rate
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Message started by ram on Jul 26^th, 2004, 10:48pm

Title: Slew rate
Post by ram on Jul 26^th, 2004, 10:48pm

Hi All,

I have some problem in understanding the slew rate in diff amp. At large swing inputs it is said that, the rate of output change will be limited by max tail bais current through Cc.

But at small swing inputs what is the limiting factor for the rate of output change.

Please guide me on this.

Regards
Ram

Title: Re: Slew rate
Post by Paul on Jul 28^th, 2004, 12:55am

Hello Ram,

At small inputs you can consider being in the so-called small-signal range of the input device of your amp. Transconductance is then defining the settling of your amplifier. In the slew-rate situation, the output voltage changes linearly over time (constant current charging a capacitor). In small signal behavior, the settling is exponential with a C/gm time constant (you will notice the similarity to a RC time constant in the passive case).

Paul

Title: Re: Slew rate
Post by mannysingh on Dec 17^th, 2004, 5:00pm

all jargon aside, when you have small signal, your output rises exponentially (like RC) but for large signal, your output rises linearly (SR = tail current / Cc).