Need of Constant Current Source:

For dual input balanced output, CMRR is given by following formula,

$CMRR=\frac{Ad}{Ac}=\frac{(re+2Re)}{re}$

Hence we can see that CMRR dependent on Re. To improve CMRR we need to increase Re. But Re cannot be increased to a great extent, since the dc current will decrease which …