I'm studying the following two-stages class AB amplifier:
Basically it is a standard two-stages op-amp (i.e. the cascade of a differential pair with active current mirror followed by an inverter with active load) to which the source follower M8-M9 has been added in order to provide the single-ended output signal of the differential pair to the gates of both M5 and M6. I have doubts about some sentences of my book.
The book says that the gain of the second stage (i.e. the inverter with active load given by M5-M6) is:
Shouldn't the gain be negative? M5 and M6 give raise indeed to an inverter.
I think that the book has an error: the gate of M1 should be in-, while the gate of M2 should be in+.
Since the book does not provide the expression of the total low frequency gain, I surmise that it is given by the product of the gains of the three stages. Is it correct to assume the gain of the source follower equal to 1 for semplicity?