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Design >> Analog Design >> Opamp input common mode voltage
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Message started by neuro11 on Mar 17^th, 2013, 8:23pm

Title: Opamp input common mode voltage
Post by neuro11 on Mar 17^th, 2013, 8:23pm

I am little confused about Opamp input common mode voltage. what i learned from a tutorial is this.

VICM = [VIN (+) + VIN (–)]/2

and

VICMR = VICMR_MAX – VICMR_MIN

Where:

VICMR_MIN = limit relative to VCC – supply rail

VICMR_MAX = limit relative to VCC+ supply rail

But thats not clear to me. Can someone explain the two parameters with some values.

Thanks in advance.

Title: Re: Opamp input common mode voltage
Post by raja.cedt on Mar 18^th, 2013, 12:43am

hello,
you are confused with two.
Vicm gives common mode when you signals applied. It is nothing to do with opamp architecture.

Vicmr_max means how max common mode you can apply to opamp and vicmr_min means how min common mode you can.

Always applied input common mode must fall in the range of vicmr_max-vicmr_min.

There is slight modification between the terms in your post and my reply, but you better follow this. Please have a look on Razavi book.

Thanks,
Raj.

Title: Re: Opamp input common mode voltage
Post by neuro11 on Mar 18^th, 2013, 1:39am

hi Raj,
thanks for nthe clarification. I can understand now.