申論題

4. (30%) Figure 4 shows a MOSFET transistor M that makes a constant current source for a 20-kΩ load. The body terminal and source terminal of MOSFET M are tied together. Assume that = 15 V, and the transistor M has the device parameters: WIL = 80, = 50 μA/V²,=0.7 V,λ = 0.1. Suppose we want to have I_D = 0.5 mA.

(b) (10%) Determine the minimum allowed that still assures that M works properly as a constant current source.