Bias current for voltage amplifier

[kbcheong]

Diagram attached showed a circuit for a voltage amplifier. Assume that the power supply voltage VDD =100V, and the resistances Rs = 22.0 ohm, and RL = 120 ohm, K = 2.0 A/V^2, VT = 2.0V. If the input bias voltage VI is 6.5, what is the bias current ID in Amperes?
May I enquire the formula for bias current?

 

[(*steve*)]

Maybe you should use the discussion forum provided for you as part of 6.002x?

 

[Harald Kapp]

We've had that problem before: https://www.electronicspoint.com/voltage-gain-amplifier-model-t246017.html
Substitute VDD=100 V in that previous post and you have the solution - unless you haven't yet solved the other assignment.

Harald

 

[Laplace]

To find the bias point for this circuit requires two equations. There is the characteristic equation for the MOSFET relating VGS to drain current, and the bias equation relating bias voltage to drain current.

ID=(K/2)(VGS-VT)^2

VI=VGS+IDxRs

Note that the characteristic equation is symmetrical around VT but is only valid for VGS>VT. Plotting the bias equation gives the bias line on the graph. Where these two plots intersect is the bias point. See attachment. If I did this right then the graph should show the same bias point you calculated.