Re: common mode feedback
You can refer to "Design of analog CMOS integrated circuits" by Razavi chapter 9 but most of its circuits are rather hard to implement .A practical CMFB circuit would be the same as the unbalanced diff amplifier (the one loaded with current mirror) but by replacing one of the input transistors by 2 parallel transistors each having its gate connected to one of the different outputs of the original amplifier and the other input is connected to Vref .