4.4.2FET放大电路的小信号模型分析法 (2)中频电压增益 gS 忽略r由输入输出回路得 Ro gS 吃=V…+8n2DR=V(1+gmB)吃 Rgl Rg2 R R Vn=-8mV、R 则A 1+8mR gs t +8 r (3)输入电阻R =F+(1+r28n)R R=R∥IR3+(Ra∥R2)通常r+(1+8n)R>IR3+(Ra∥R2) 则R≈R3+(R1∥R2 HOME (4)输出电阻「R≈R BACK NEXT(3)输入电阻 (4)输出电阻 忽略 rd V i = Vgs + g m V gsR (1 m ) =V gs + g R V o = g m VgsRd − AVm = g R g R m m d 1+ − // Ri Ri = 由输入输出回路得 则 g i i I V R = [ ( // )] Rg3 + Rg1 Rg2 (1 ) [ ( // )] gs gsgm R Rg3 Rg1 Rg2 通常 r + + r + 则 ( // ) Ri Rg3 + Rg1 Rg2 Ro Rd = rgs + (1+ rgsgm )R gs gs m gs gs gs gs ( ) r V g V R r V V + + = 4.4.2 FET放大电路的小信号模型分析法 (2)中频电压增益