多级共射电路高频段近似计算及实例分析

APPROXIMATE CALCULATION AND EXAMPLE ANALYSIS OF MULTIST AGE COMMON EMITTER AMPLIFIR AT HIGH FREQUENCIES

将求多级共射电路高频段频率响应的问题，近似分析为将等效电路简化为低通网络级联形式。引入一精确方法（特别在计算上限频率ｆ＿ｋ时）与前者近似法进行比较分析，以典型实例计算ｆ＿ｈ，较方便地给出前者计算误差：二级电路时在１０％以内，四级电路时已达２０％以上（信号源内阻Ｒ＿ｓ应较小）；又在较宽频率范围内讨论了波特图（幅频），论证了２种方法的理论依据，指明误差存在原因。

In order to solve multistage CE(common emitter)amplifier response at high frequen-cies,the approximate methods are that the modified eQuivalent circuit has cascade connectionof low-pass networks. Another method is nearly accurate,specilly,when calculation of up-per frequency fh.Both the former and the latter are compared.By caculation of practical ex-amples,the result shows that fh error of the former is less than 10%when two-stage circuitand more than 20%when four-stage(but the source resiStance Rs must be small).On theother hand,the Bode plot(gain-frequency)is ploted at high frequencies.Last,evidence oftwo methods is demonstrated and cause of created error is explained.