The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> what are these two circuits?
https://designers-guide.org/forum/YaBB.pl?num=1539289557

Message started by alan kim on Oct 11^th, 2018, 1:25pm

Title: what are these two circuits?
Post by alan kim on Oct 11^th, 2018, 1:25pm

What are this circuit? It looks like some sort of current mirrors but I am trying to understand what it is and what the merits/drawback of it. Has anyone seen this before? Appreciate that you share your experience!

Title: Re: what's these two circuits?
Post by alan kim on Oct 11^th, 2018, 1:26pm

And also this

Title: Re: what are these two circuits?
Post by vroy_92 on Oct 21^st, 2018, 3:58pm

For circuit #1, note that the drain node of M3 is a very low impedance node. It is a form of regulated cascode I believe if the input is Vbn. What is the input node for this circuit?

For circuit 2, note that current through M3 is always constant. If output voltage goes up by v1, then gate of M1 and M3 will also go up by v1. Because the input current is constant, Vgs,M1 is constant. and therefore the source of M1 (which also happens to be the drain of M2) will also go up by v1. Thus, from a small signal point of view the drain voltages of the current mirror pair (M2,M4) follow each other. This makes it a very good current amplifier/buffer.