| 摘要 |
PURPOSE:To attain tuning to a desired broadcast frequency by controlling a local oscillation frequency on the basis of the difference between an intermediate and a reference frequency. CONSTITUTION:The intermediate frequency of a two-step intermediate frequency circuit 6 is converted by a frequency counter 11 into a digital signal, which is compared by a digital comparator 13 with digital data corresponding to the reference frequency from a proper frequency storage circuit; when it is within a proper range, a high-level control output is supplied from the digital comparator 13 to a control circuit 10. The frequency division ratio of a programmable divider 91 is controlled by the signal from the control circuit 10 to divide the frequency of a local frequency oscillation circuit 3. This divided frequency is compared by a phase comparator 93 with the output of a crystal oscillator 92 and the oscillation frequency of a local oscillation circuit 3 is controlled by the comparison output to attain electronic tuning. Further, when an automatic search command signal is supplied to the control circuit 10, another frequency division ratio of the programmable divider 91 is selected. |
