四、如圖四之電流放大器型反饋電路,不考慮通道長度調變(channel length modulation),假 設 Q1 、 Q2 之 gm1 = gm2 = 5 mA/V , R D = 20 kΩ , R M = 20 kΩ , RL =1 kΩ ,RF = 80 kΩ,求開迴路電流增益(open loop gain)A =?反饋因數(feedback factor)β =?以及閉迴路電流增益(closed loop gain)Af =?(20 分)