| 摘要 |
PURPOSE:To obtain a signal component, while an S/N is improve by means of using a ready- made BPF by making a light receiving element operate at a clock angular frequency, and preparing an optional angular frequency omegao by an oscillator. CONSTITUTION:A CCD 1 outputs the video signal of the angular frequency omegap, corresponding to the clock of the angular frequency omegac. The oscillator outputs the oscillation signal of the angular frequency omegao. A non-linear type circuit 2 operates as a mixer, and mixes the above mentioned video signal and the oscillation signal of the oscillator 3. As the result, the output of the non-linear type circuit comes to be a signal, which has an angular frequency spectrum like a figure (b). This output signal is inputted to the BPF 4, and the output signal of it comes to be the signal, which has the spectrum at the angular frequencies omegao-omegac, omega0-omegac+ or -omegap. This output signal is made to pass through a detection circuit 5, which has a non-linear type element, and LPF 6 and an amplifier 7, and the signal, that the video signal of the angular frequency omegap is amplified, is obtained. In this case, the circuit of the figure A is inserted between the BPF 4 and the detection circuit 5. After the output signal of the BPF 4 is amplified by the amplifier 8, the central part of it, which has no influence on an envelope, is removed by a slice circuit 80, and it is inputted to the detection circuit 5 through the BPF 9. As the result, the S/N is improved.
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