aamar
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Posts: 57
Germany
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If you want to look for it as a group of current mirrors, then your circuit includes two current mirrors. The first is P1/P2 and the second is N1/N2. From the first mirror Ibias will flow also in P2/N1 in steady state, biasing the source of N1 to Ibias*Rleft. Rleft is used to stabilize the operating point, by its negative Feedback effect on N1, because when current increases in P2/N1 for any reason, the drop on Rleft will increase the source node voltage of N1 high (above the steady state value), reducing the Gate-Source voltage of N2, which will reduce the current back to the steady state value (biasing circuit). The second current mirror between N1/N2 will bias the P3/N2 with the same current Ibias, which will adjust the source of the N2 to Ibias*Rright, the same like we mentioned before the Rright will have a negative Feedback effect on the source follower N2, but this time the current change will be intentionally using the Iin, in the way that when it is high enough above a certain threshold current it will raise the source node voltage of N2 to a level which can turn N2 off (given that the gate voltage of N2 is constant, from the bias circuit), then when it is turned off the output of P3/N2 will be VDD, which will be further amplified by the output stage (P4/N3) (driving the N3 strongly ON) so the Sou will be low (conclusion: Iin is High, Sou is low) and you can conclude the second case when Iin is negative. I wish my discussion was clear.
Best regards
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