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下面的电路是使用场效应晶体管斩波器的低漂移直流放大器,由输入端接入的直流信号经Q_1(FET)斩波变换成交流信号,再由交流放大器Q_2、Q_3、Q_4放大100倍,在交流放大器中,流过Q_4的电流再反馈到Q_2输入端,因此,这级的电压增益差不多取决于R_8与R_(11)的比值。R_(10)、R_5是Q_2偏置电阻,并通过它对直流提供5%的负反馈。Q_4的集电极电平的平均值保持在7.5V左右,Q_5是同步整流器,它把被放大的交流信号再变换成直流信号。IC是运算放大器,它把整流后的信号放大1000倍作为输出电压。输出电压通过R_9负反馈到Q_1的源极,放大器的全部增益几乎完全决定于R_9与R_3之比,图示的情况下,约1000倍。Q_6、Q_7是双稳多谐振荡器,由它驱动Q_1和Q_5,振荡周期由R_(24)、C_1和C_2、R_(25)决定,图示的情况下约200HZ。
The following circuit is a low drift dc amplifier using a field effect transistor chopper. The dc signal from the input is chopped into an ac signal by Q_1 (FET), amplified 100 times by the ac amplifiers Q_2, Q_3, Q_4, In the AC amplifier, the current through Q_4 is fed back to the Q_2 input. Therefore, the voltage gain at this stage depends almost on the ratio of R_8 to R_ (11). R_ (10), R_5 is the Q_2 bias resistor and provides 5% negative feedback to the DC through it. The average collector level of Q_4 remains about 7.5V. Q_5 is a synchronous rectifier that converts the amplified AC signal into a DC signal. The IC is an operational amplifier that amplifies the rectified signal 1000 times as the output voltage. The output voltage is negatively fed back to the source of Q_1 through R_9. The overall gain of the amplifier is almost completely determined by the ratio of R_9 to R_3, which is about 1000 times as high as the case shown. Q_6 and Q_7 are bistable multivibrators driven by Q_1 and Q_5. The oscillation period is determined by R_ (24), C_1 and C_2, R_ (25), and is about 200HZ in the illustrated case.