SIMILAR QUESTION

For OP-AMP explain CMRR

Input modes:

Single ended mode: If i/p sig is applied only to one of the i/p and other i/p terminal is connected to grid. OPAMP is said to be operating in the single ended mode.

The i/p and o/p signal are 180 degree out of phase

If i/p is applied to inverting i/p

The i/p and o/p signals are in phase with each other

If i/p sig is applied to non- inverting i/p

Differential mode : In this, 2 opposite polarity last of phase sig are applied to the 2 i/ps of OP-AMP

This type of operation is double ended operation. The difference between i/p sig is amplified appears at o/p.

Common mode: (CM)

In CM, the same i/p signal is applied to both i/p terminals

Ideally a O o./p voltage should be produced by the OP-AMP.

Producing a zero o/p for a common mode signal is called as common mode rejection.

Common mode rejection radio (CMRR):

The signal which is present at both the i/p terminals of an OP – AMP is called as common mode signal.

The best e.g. is “noise “. The OPAMP should produce a very small o/p voltage corresponding to common mode signal. In other words it should be capable of “rejecting” the common mode signal. CMRR is the ability of differential amplifier to reject the common mode signal successfully. It is called as figure of merit of OP-AMP

Ideally, OP-AMP should produce very high gain for desired sig, i.e., single ended or differential signals..

The value of CMRR should be ideally infinite and practically as high as possible.

$CMRR = Av/ A_{cm}$, Av= open loop gain of OP-AMP

$A_{cm}$= common mode gain of OP-AMP.

Open loop voltage gain is voltage gain of an OP-AMP in the open loop mode (without any feedback) of OP-AMP and it is very high.

In decibels, $CMRR (dB) = 20 \log_10 [Av/A_{cm}]$