| 摘要 |
<p>The circuit comprises a variable gain amplifier (VCA) (71) supplied with a process signal (S55), a signal processor (72-74) for detecting and calculating the level of either the process signal or an output signal of the VCA and the level of a control signal (S56), and outputting a gain control signal (S60) in accordance with the level difference between them. A voltage output type amplifier (77) is switchable to either a normal operating state for delivering at its output terminal the gain control signal obtained from said signal processor or a signal interrupting state for retaining said output terminal at a high impedance state. A converter (78) converts the output voltage of the amplifier (77) into a current and voltage holding means (75) generate a voltage proportional to the current supplied thereto from the converter (78). The VCA (71) amplifies the process signal according to the output voltage of the voltage holding means (75). The servo circuit is adapted for controlling a variable gain amplifier to process an audio signal in a television receiver, a stereo apparatus or the like. When the servo circuit is formed into an IC configuration, a high-precision operating characteristic is attained merely by a bipolar-transistor manufacturing process to consequently minimize the number of required process steps, hence curtailing the production cost. <IMAGE></p> |
