| 摘要 |
An audio circuit of a complex tuner is provided to prevent a noise of a channel audio signal when selecting a channel after converting a system according to a transmission method. An audio intermediate frequency amplifier(21) amplifies an audio intermediate frequency. An FM detector(22) detects the amplified audio intermediate signal as an audio signal with high sensitivity. An FM PLL(Phase Locked Loop) filter(23) controls the gain of the detected audio signal. An amplifier(24) amplifies the audio signal detected by the FM detector. A de-emphasis circuit(25) attenuates the audio signal amplified by the amplifier and restores the original audio signal. A noise preventing unit(26) prevents the influence of an audio oscillation signal by reducing the voltage around the boundary of the system in an FM PLL filter. |
