D 9.19 Figure P9.19 shows a MOS differential amplifer with the drain resistors R D implemented using diode-connected PMOS transistors, Q3 and Q4. Let Q1 and Q2 be matched, and Q3 and Q4 be matched.(a) Find the differential half-circuit and use it to derive an expression for Ad in terms of gm1,2, gm3,4, ro1,2, and r o3,4. (b) Neglecting the effect of the output resistances ro, find Ad in terms of μn, μp, (W/L)1,2 and (W/L)3,4. (c) If μn = 4μp and all four transistors have the same channel length, find (W1,2/W3,4) that results in Ad = 10 V/V.