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直流对数放大器是放大倍数随输入信号的大小按对数规律变化的直流放大器。这种放大器输入动态范围大,输入和输出成对数关系。一、直流对数放大器的基本原理直流对数放大器由直流放大器和提供对数特性的反馈元件两部分组成。提供对数特性的反馈元件通常是晶体二极管或是接成二极管形式的晶体三极管。图1是直流对数放大器的原理图。从图1中可以看到,由于直流放大器A的反馈元件的电压与电流的对数成比例,因此,使整个放大器的输出电压与输入电压的对数成比例。其数字表达式为 (1)式中L_ε是反馈元件BG的发射极-基极结反向饱和电流;α是一常数。证明如下:
DC logarithmic amplifier is the magnification of the logarithm of the input signal with the size of the DC amplifier. This amplifier input dynamic range, input and output logarithmic relationship. First, the basic principles of DC log amp DC log amp from the DC amplifier and the logarithmic characteristics of the feedback components of two parts. The feedback element that provides logarithmic characteristics is usually a crystal diode or a diode in the form of a diode. Figure 1 is a DC logarithmic amplifier schematic. As can be seen in Figure 1, since the voltage across the feedback element of the D.C. amplifier A is proportional to the logarithm of the current, the output voltage of the entire amplifier is proportional to the logarithm of the input voltage. The digital expression is (1) where L_ε is the emitter-base junction reverse saturation current of the feedback element BG; and α is a constant. Prove as follows: