vivkr
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Hi Steven,
If you are designing to include functionality for both differential and single-ended operation, you will use a fully differential structure anyway, and either accept the penalty in SNR from using a single-ended input, or overdesign for the differential case. For a high-performance design, you prefer this option.
If you do wish to design a single-ended structure only, then I suppose you are referring to the degradation in the AC response caused by the mirror. Typically, this is fixed by careful design.
You could use an NMOS input and diode-connect the current sources on the NMOS side. This offers double the slew rate compared to diode-connecting the PMOS devices on top of the folding nodes, and has better CMRR. However, the zero is worse here. However, the extra slewing current allows you to compensate the opamp a little more easily.
I hope this is helpful for you. Perhaps others can offer their comments.
Regards Vivek
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