I'm just going through amplifier circuits and I'm having some trouble with amplifiers in which the MOSFET is biased by a constant current arrangement. Here's my issue:
In the MOSFET saturation equation, if we set ID, we will be able to obtain Vgs. Which means that if we plug in the value of I into that saturation equation, it will tell us what Vgs value we need to have between the gate and source for us to achieve that specified current I as Vgs determines the resistance of the MOSFET internal channel and hence the current.
Now, how come in this arrangement, there is no voltage at the gate? Wouldn't that mean that no channel has been established and hence current could never flow? Or is there assumed to be a DC bias voltage at the gate? If there is a DC bias voltage assumed at the gate, wouldn't it be considered biased by a gate voltage and not by a current source? Or is it assumed that the current source dictates what Vgs bias voltage is required and that whatever bias voltage that current source requires will always be present for it?
I have all these doubts that I can't find answers to.