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I want to know why we use op amplifier. We can bias directly from some biasing circuit to vco. But why we use op amp between baiasing ckt and vco.
um. I think input impedance of op amp is infinity. Thus if we use op amp between biasing ckt and vco, the vco will not affect to biasing circuit. But if we directly bias vco then it's finite input impedance will affect to the biasing circuit. Is it right :?:
Replicate biasing circuit is a simple straightforward method to ensure that bias current in the active circuit to be biased is exact the refernce current or a fixed ratio to them.
The design principle is that the active part of the circuit is duplicated and driven by a reference current. The voltages of the biased devices in the replicate circuit are then used to bias the active stages. So the bias current in the active stages mathc very close the reference current.