| 摘要 |
An automatic switching control circuit is responsive to a command signal as derived from manual tuning operation to change the operating modes of a feedback-controlled system such as automatic frequency control circuit, and includes a first impedance element, an inverting amplifier and a second impedance element in a series circuit between an input terminal to which an error signal from the feedback-controlled signal is applied and an output terminal from which a compensation signal is applied to a modulating element of the feedback-controlled system. A third impedance element is connected between the output terminal and a reference terminal. A switch is provided to establish a short circuit path between the input of the inverting amplifier and the output terminal. The voltage across the third impedance element automatically reduces to substantially zero voltage level in response to the presence of the short circuit path so that the feedback control is suspended. The voltage across the second impedance may be utilized to indicate the signal level of the error signal during the open and closed loop control modes.
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