| 摘要 |
PURPOSE:To send a signal from DC to a high frequency without using a special complicated expensive circuit and decreasing the upper limit of the transmission frequency band by using a sampling filter so as to obtain a potential representing a zero level and other potential thereby reproducing the zero potential. CONSTITUTION:A transmission signal from a transmitter 10 is received by a reception circuit 21 in a receiver 20 and demodulated by an IF conversion demodulation circuit 22. The demodulated signal is similar to a modulation waveform outputted from a switch circuit 13 and the DC component is fluctuated by a carrier frequency, e.g., temperature change. The demodulation signal is fed to a PLL 23 and a sampling filter 24 and the PLL 23 extracts the signal of the same period of the zero level synthesized by the transmitter 10 from the demodulation signal, that is, the output signal of an oscillation circuit 12. Since the zero potential is reproduced by obtaining a difference between the potential representing the zero level and other potential by the sampling filter in this way, even when the level of the reception signal and its demodulation signal is suddenly changed, no effect is received.
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