| 摘要 |
PURPOSE:To perform phase lock detection securely by adding a function for frequency decision as well as level decision. CONSTITUTION:A digital comparator 32 performs a digital comparison between a frequency at a modulation terminal 7 and the frequency of the output signal of an AC amplifier 31 which is counted by a counter to generate an H-level output only when the both coincide with each other, or an L-level output when not. An AND circuit 36 has a level H only when the control voltage of a voltage-controlled oscillator VCO7' contains no AC component and a DC component within some level range. An OR circuit 37 has a level H when either of the comparator 32 and circuit 36 generates the H-level output. Therefore, only when the modulator is locked, an H-level signal appears at a terminal 38, so this signal is utilized to obtain a lock signal easily. |
