场应管)2.动态指标分析 gmY gs (2)中频电压增益 Rg3 gS 忽略r由输入输出回路得 Vi Rud rgz R V=Vo+8mL R=Vs(1+gmR) 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 NEXT4.4 结型 场效应管 2. 动态指标分析 （2）中频电压增益 （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     + + =