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概述

Fig. 8.1 shows a negative-feedback system.

• $H(s)$ is called the feedforward networks or jopen-loop transfer function
• $G(s)$ is called the feedback networks
• the input to $H(s)$ is $X(s)-G(s)Y(s), called the feedback error

The close-loop transfer function is

$$ Y(s) = H(s) [X(s)-G(s)Y(s)]\\ \frac{Y(s)}{X(s)} = \frac{H(s)}{1+G(s)G(s)} $$