| 摘要 |
PURPOSE:To obtain a digital band pass frequency detecting circuit not using any capacitor by inputting an output of a pulse generator and an output of pulse signal to a digital phase comparator and connecting an output to a clock input of the counter. CONSTITUTION:In inputting a frequency fo of a pulse generator 1 and a pulse signal frequency fi to inputs CG and SG of a digital phase comparator 2 respectively, in case of fo>fi, since the frequency less than the fo is outputted as a digital pulse and no frequency over the fo is outputted, the detected upper limit frequency is decided by the fo. When the pulse signal fi is outputted, the signal is latched by a set input S of a flip-flop 5 and its output Q is inputted to an enable input E of a counter 6, which is in standby state and counts a pulse of fo>fi of the comparator 2. The output fo of the pulse generator 1 is inputted to a clock input CLK 1 of the counter 3 to count the fo.
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