| 摘要 |
PURPOSE:To accurately remove a noise by executing the detection after being amplified with a high frequency amplifier for receiving a signal and further, detecting a noise component included in the A/D-converted signal after it is amplified by the high frequency amplifier for receiving a noise. CONSTITUTION:Since the high frequency amplifier 21 for receiving a signal and a high frequency amplifier 22 for receiving a noise are one and the same characteristic, a noise component (Vn+Vin) included in the digital output Fd1 of a first A/D-converter 26 becomes equal to the noise component (Vn+Vin) of a digital output Fd2 of a second A/D-converter 29. Consequently, when the exclusive OR of these Fd1 and Fd2 is obtained, a noise component Vn and an internal noise Vin included in an objective signal Vs are cancelled and only the signal component of Vs can be obtained at the digital output of a digital comparator 30. After a digital output Vs is converted to an analog signal by a D/A-converter 31, it is amplified by an output amplifier 32 and removed as the low frequency signal without having a noise.
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