| 摘要 |
PURPOSE:To prevent malfunction of a digital circuit by detecting an input level by a comparator at the time of fading in which the input level is dropped in time and letting a clock oscillator to self oscillate so as to attain waveform shaping. CONSTITUTION:An intermediate frequency protection circuit 26 consists of a comparator, a clock oscillator and a logic circuit. The logic circuit of the circuit 26 outputs with a clock pulse from the clock oscillator usually synchronized with rising of an output of the comparator and outputs a clock pulse from the clock oscillator oscillating with a frequency close to an intermediate frequency when the rising of the output of the comparator does not come within a prescribed period of time. Thus, an omitted pulse at fading is prevented. Since an output of the circuit 26 is inputted to a counter 21, which counts the output, an event of counting a random frequency at the time of fading is prevented and the oscillating frequency of a voltage controlled-temperature compensation quartz oscillator VC-TCXO 25 is more accurately controlled. |
