9.71 An NMOS differential amplifier for which the MOSFETs have a transconductance parameter kn and whose drain resistances R D have a mismatch RD is biased with a current I. (a) Find expressions for Ad and VOS in terms of kn, RD, R D/RD, and I. Use these expressions to relate VOS and Ad. (b) If kn = 4 mA/V2, RD = 10 k, and RD/RD = 0.02, find the maximum gain realized if VOS is to be limited to 1 mV, 2 mV, 3 mV, 4 mV, and 5 mV. For each case, give the value of the required bias current I. Note the trade-off between gain and offset voltage.