PURPOSE: To obtain a narrow band frequency discrimination circuit transmitting only a frequency signal being an odd number of times of the sampling frequency by supplying an input signal having a frequency band including a signal being an odd number of times of the sampling frequency.
CONSTITUTION: A signal at an input terminal is fed to a switched capacitor filter operated according to the sampling signal set to a frequency being 1/(2N+1) of the specific frequency included in the signal frequency band so as to send the specific frequency signal having an odd number (2N+1) times of the frequency of the sampling signal. For example, an input signal Vin is fed to one electrode of an input capacitor CI via a switch means SI and the other electrode is coupled with an inversed input terminal (-) of an operational amplifier circuit OP. A feedback capacitor Cf is provided between the inversed input terminal (-) and an output terminal of the operational amplifier OP. Further, a capacitor C2 whose one electrode is connected to a ground potential and whose other electrode is connected laternately to the inverting input (-) and the output terminal of the operational amplifier circuit OP via a changeover switch means S2 is provided.
FUJII FUMIAKI
SAKAGUCHI JIRO
