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Design >> Analog Design >> Input common mode in differential amplifier
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Message started by giri_lp on Aug 13^th, 2009, 6:21am

Title: Input common mode in differential amplifier
Post by giri_lp on Aug 13^th, 2009, 6:21am

How do we have to understand the Vin CM in a differential amplifier? Is that the offset from 0 or it is DC CM or AC CM of the signal? Please explain this.

Title: Re: Input common mode in differential amplifier
Post by raja.cedt on Aug 16^th, 2009, 10:36pm

hi,
i didn't understand your question properly..but generally opamp input they divide into common mode (dc) +differential mode (ac)....there is no question offset here.........

Thanks,
Rajasekhar.

Title: Re: Input common mode in differential amplifier
Post by aamar on Aug 17^th, 2009, 12:31am

It is the in phase part of the 2 input signals either it is DC or AC. Normally it should be a DC signal in order to keep the operating points of the devices at a fixed point but it can contain also an AC component which has to be attenuated by the amplifier itself. The ability of attenuating the AC common mode signal at the inputs is the CMRR of the differential amplifier.

Best regards,

aamar