| 摘要 |
<p>A tune detecting circuit that is used, for example, for an FM radio receiver and that has the function of detecting the mute band. The tune detecting circuit helps solve the problem related to setting a band ratio of the tune detecting band to the non-mute band. For this purpose, a resistor for setting a band to be detected is provided between an end of a capacitor that removes AC signals included in the FM detect signals and an end of the power source that supplies reference power source. An input terminal of a first buffer circuit is connected to a point where the resistor and the capacitor are connected together, and an input terminal of a second buffer circuit is connected to a point where the resistor and the power source are connected together. A tuning band detector that detects the tuning band is connected to the output terminals of the first and second buffer circuits. A detuned mute band detector that detects the detuned mute band is provided between any divided point of the resistor and an end of the power source. In response to an output signal from the detuned mute band detector, the mute circuit controls the gain of an amplifier that amplifies FM detect signals.</p> |
