Another equation, which models the velocity-saturated drain current of an MOS transistor is given by

Using this equation it is possible to see that velocity saturation can be modeled by a MOS device with a source-degeneration resistor.

a. Find the value of RS such that IDSAT(VGS, VDS) for the composite transistor in the figure matches the above velocity-saturated drain current equation. Hint: the voltage drop across RS is typically small. Channel length modulation can be ignored.
b. Given Esat = 1.5 V/µm and k’ = µ0Cox = 20 µA/V2, what value of RS is required to model velocity saturation. How does this value depend on W and L?