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Transistor Saturation

For the circuit of the figure attached, determine the required values of Rd, R1 and R2 so that the transistor operates in the saturation region with Id=0.5mA and Vd=3V. The enhancement mode PMOS transistor has Vt=-1V and K=0.5mAV^-2. What is the largest value Rd can have while maintaining the transistor in saturation?


Solution Preview

1. Rd = Vd/Id, really simple.

2. Calculate Vgs, which is the gate-source voltage. knowing Vgs will help to get the voltage drop on R1: Vr1. The Voltage drop on R2 is simply Vdd - Vr1.
Notice that Saturation Voltage Vsat is Vdd - Vd = 2v.
See the following equations:
Id = (B/2)(Vgs-|Vt|)^2, (eq1) Id is the current at ...

Solution Summary

Here are the explanations how to solve the problems. Only equations and method are provided while most of the values need to be calculated by yourself. That's just simple algebra. 275 words.