Can anyone help me in designing a common mode feedback circuit (CMFB). I have applied a 100mV DC common mode input voltage at the input of a differential pair with no Ac signal. My fully differential amplifier output common mode DC voltage is 456mV at one end and 450mV DC voltage on the other end of the differential amplifier. Now what Vref should I place at the Vref of the CMFB circuit?

I have read somewhere it should be at the mid supply voltage. I have used +/- 1V supply means do I have to place the vref at 1V or 0.5V.? what should be the region of operation of the transistors in CMFB circuit. Does the Gain of the common mode feedback not show any impact on the fully differential amplifier?

can any one explain in detail