| 摘要 |
PURPOSE:To enable to obtain correct tuning without adding external circuits, by controlling the local oscillator so that the IF of a tuner is compared with specified IF for coincidence. CONSTITUTION:When the signal of desired channel is input to the CPU3 from the input unit 1, the CPU3 reads out the local oscillating frequency fL corresponding to the channel and stores the data. The oscillation output from the local oscillator of the tuner 6 is counted at the counter 9, the count value is input to CPU3, and it is compared with the data in frequency fL stored in the CPU3, and the charge pump 8 is controlled the output of local oscillator can be within the specified frequency range. When the oscillation frequency of local oscillator is within the specified range, the IF signal of the tuner 6 is counted at the counter 9, the count value is input to the CPU3, it is compared with normal IF, the charge pump 8 is controlled so that it corresponds with the normal IF to control the oscillation frequency of the local oscillator. Accordingly, without AFC circuit externally, the accurate IF can always be obtained. |
