The Loop Gain of Wilson Current Mirror

[fhongjin]

Hi,
Could someone please help me understand the underlined statement? I tried to draw an equivalent small signal model of this Wilson Current Mirror but I could not get the same conclusion as mentioned in Allen's book. Did I make some mistake in my small signal model? Thank you for replying in advance.

 

[Jerry.YL]

Maybe you misunderstood the statement. In regard to loop gain, you need to break the loop at gate of M3 and calculate the transfer function from the breakpoint to the drain of M1.

 

[fhongjin]

Maybe you misunderstood the statement. In regard to loop gain, you need to break the loop at gate of M3 and calculate the transfer function from the breakpoint to the drain of M1.

Ahhh. So we are actually calculating voltage gain here right? I am still a little bit confused: why not the current gain? The main purpose of this architecture is to stablize output current right?