15.31 Figure P15.31 shows a PMOS transistor operating as a switch in the on position. (a) If initially vO= 0 and at t = 0, vI is raised to VDD, what is the final value VoH reached at the output? (b) If initially vO = VDD and at t = 0, vI is lowered to 0 V, what is the final value VOL reached at the output? (c) For the situation in (a), find tPLH for vO to rise from 0 to VDD/2. Let kp = 125 uA/V^2, VDD = 1.2 V, and |Vtp| = 0.4 V.