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利用晶体三极管的非线性特点,我们可以做出具有对数特性的放大器.在输入信号很小时放大器的增益很高,但当输入信号继续增大时放大器的增益即下降.图1为此放大器的输入输出特性. 电路由四级运算放大器组成,如图2所示.运算放大器F_1、F_2组成同相输出放大器.W_1用来调节零点,当无输入信号时,G点输出电压U_1应为零. 运算放大器F_3与BG_1组成对数放大器,其工作原理如下:因为晶体三极管的集电极电流I_c为
The use of the transistor nonlinear characteristics, we can make an amplifier with logarithmic characteristics of the amplifier input gain is very high, but when the input signal continues to increase the gain of the amplifier that is reduced. Input and output characteristics of the circuit consists of four operational amplifiers, shown in Figure 2. Operational amplifier F_1, F_2 constitute a non-inverting output amplifier .W_1 used to adjust the zero point, when there is no input signal, G point output voltage U_1 should be zero. Amplifier F_3 and BG_1 composed of logarithmic amplifier, its working principle is as follows: Because the transistor transistor collector current I_c is