Increasing the Bandwidth of Differential Amplifier
Examine this circuit; each of the diffpairs has gain of 8X at low frequencies; but their F3dB (45 degree point) are not consistent; why?





And Q7/8 do not have gain of 8X. Why?

Also notice the leftmost diffpair has no source resistor, thus CMiller can be infinite but the SPICE source handles the input current (Ibase, Cob) just fine; on the other hand, the 3 right circuits include Rin, and that R along with Cmiller impacts the circuit bandwidth.