| 摘要 |
PURPOSE:To obtain a signal processing circuit capable of detecting a reference wave period by a simple constitution by successively comparing a rising period and a falling period and detecting the slit of the reference wave period based upon the compared result. CONSTITUTION:In an electronic instrument 10, a microphone 2 picks up humming and applies an obtained sound input signal SA to a waveform shaping circuit 11 through an automatic gain control circuit 3. The circuit 11 is constituted of a comparator and outputs a waveform shaping signal SH whose signal level is rised when the signal SA is raised from the '0' level. The circuit 11 constitutes the 1st period detecting means for successively detecting periods T1 to T5 obtained from the rising of the signal SA from the '0' level up to the 2nd rise to the '0' level or the period from the falling of the signal SA from the '0' level up to the 2nd fall to the '0' level. |
