| 摘要 |
PURPOSE:To obtain a circuit capable of detecting specific frequency signals within a short space of time by a comparison detecting direct current on the theory of the formulaIin a circuit for detecting whether or not input signals meet a specified frequency. CONSTITUTION:Frequency signals to be detected are set at Asin(omega1t+theta) among those inputted from an input terminal 1. When carriers outputted from a carrier supply oscillation circuit 12 are set at Bsinomega2t, the value turns to Bcosomega2t after the carriers pass through a phase shift circuit 11 for advancing the phase by 90 deg.. Therefore, signals in formulas II and III are obtained by passing outputs of a modulation circuit 2 receiving input signals and a circuit 12 and outputs of a modulation circuit 3 receiving input signals and a circuit 11 through LPFs 4 and 5. Signals thus obtained are applied to a summing circuit 8 through squaring circuits 6 and 7 and outputs of a root circuit 9 turns to d.c. signals of (AB)/2 which are checked for the presence of signals to be detected with a comparator 10. Therefore, coinciding the frequency of supply carriers with the frequency to be detected enables the detection of specified frequency signals. |
