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自动增益控制(AGC)系统中的非线性是一个突出的问题。和一般的控制系统不一样,它的非线性包含在执行元件中。对于一阶和阶跃输入的情况,本文以状态转移法分析了这种非线性离散系统,并以简单的图解法描绘了状态转移过程。对于高阶和信号幅度任意起伏的情形,则把AGC系统等效为一个易于分析的“标准”的控制系统。这个等效无论对离散系统或连续系统都是严格成立的。文中提出了使AGC系统线性化的方法,它用对数放大器作非线性校正,使具有严重影响的非线性AGC系统变为线性系统。还进而提出了两个互为对偶的应用:一个是利用增益控制原理求出信号幅度的对数值并使之数字化,另一个是用模拟式对数放大器作开环增益控制。
Nonlinearity in automatic gain control (AGC) systems is a prominent issue. Unlike general control systems, its nonlinearity is contained in the actuator. In the case of first-order and step-input, the nonlinear discrete system is analyzed by the state transition method and the state transition process is depicted by a simple graphical method. For high order and arbitrary fluctuations in signal amplitude, the AGC system is equivalent to a “standard” control system that is easy to analyze. This equivalence is strictly established for both discrete systems and continuous systems. In this paper, a method of linearizing the AGC system is proposed, which uses a logarithmic amplifier for nonlinear correction, which makes the nonlinear AGC system with serious influence become a linear system. Furthermore, two dual applications are proposed: one is to use the principle of gain control to find and digitize the logarithm of signal amplitude, and the other is to use an analog logarithmic amplifier for open-loop gain control.