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what are these two circuits? (Read 243 times)
alan kim
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what are these two circuits?
Oct 11th, 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!
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alan kim
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Re: what's these two circuits?
Reply #1 - Oct 11th, 2018, 1:26pm
 
And also this
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vroy_92
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Re: what are these two circuits?
Reply #2 - Oct 21st, 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.
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V Roy
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