Two question about Op amp with single-ended output

[wangkes9]

Like the attached ，cited from Razavi’s book.

1.The total capacitance at this node A roughly equal to CgS5 + CG56 + CDB5 + 2CGD6 + CDb3 + CGd3, Why 2 * Cgd6 ，is this miller effect. So the Av must to be -1 from Gate6 to drain6. How to get this number?

2.There is two paths from input to the output.The poles of A and N only affect path 1 , so in the total transfer function ,these poles only play a role of 50%.
Why in the frequency response picture of the book, it seems these two poles is a factor in whole transfer function (100% effect).

 

[ict_eda]

wangkes9,

Question 1: The impedance seen in N towards M7 is approx. 1/gm7. If M6 and M7 are identical, the gain from the gate of M6 to the drain of M7 is -gm6/gm7 which is considered to be close to -1.

Question 2: On page 357 the author describes the effect of the pole(s) of the current mirror as an overall zero in the input-output transfer function. Please read carefully.


ict