Re: folding amplifier
Use an active load. The problem with this folding circuits is the huge DC value of the current (4Xtail current in eachh branch of the output) while only one tail current is used to charge/discharge the load capacitor. So you will have to use a bypass: two current mirros will take most of the DC current, and in parallel you have a diode connected transistor (or an R), but only a small part of the current flows there => you can increse the resistance.
You will never get good BW with this configuratin becuase the Cgd of 8 (or 9) pairs apper as a load. You want more current, but you will have the same ΔVref, so u want same Vgs, so you have to increase trasistors => increased Cgd=> speed stays the same.