| 摘要 |
PURPOSE:To detect the frequency accurately by adding an envelope generating circuit and a zero cross detection circuit for the envelope to a frequency detection circuit so as to utilize the envelope waveform thereby eliminating a part with the synthesized component undetected therefrom comprising two different kinds of frequencies. CONSTITUTION:An envelope generating section 1 applies peak hold to a waveform resulting from full-wave rectifying to an input signal to generate an envelope. The envelope is detected by a zero cross detection section 2 to form bipolar rectangular waves with respect to a O level and they are inputted to a synthesis component frequency detection section 3. The synthesis component frequency detection section 3 receives a synthesis component signal of two different kinds of frequencies and masks a positive portion of the rectangular wave of the envelope frequency from the zero cross detection section 2 and outputs part of the frequency to a counter section 4 as a rectangular wave. The counter section 4 counts the period of the rectangular wave resulting from zero cross detection of the unmasked part to detect the synthesized component frequency. Thus, the envelope of the signal waveform comprising two different kinds of frequencies is used to detect the synthesis component frequency accurately. |
