PURPOSE: To miniaturize a device by detecting the upper limit voltage value and the lower limit voltage value of a dynamic range of an output voltage of a charge coupling device, operating its average voltage value and comparing the value with the output of a reference charge coupling device so as to eliminate the need for the adjustment of a DC bias of an input section.
CONSTITUTION: Assuming the output of a means 45 detecting the upper limit voltage value of the output voltage dynamic range of the charge coupling device be E1 and then the output of a means 46 detecting the lower limit voltage value be E2, then the two voltages E1, E2 are inputted to a average voltage value detecting means 47 to obtain a voltage value of (E1+E2)/2 from the output. The voltage (E1+E2)/2 and output of the reference charge coupling device 48 are inputted to a comparator 49 to compare the voltages. After an error output being the result of comparison is amplified by an error amplifier, the result is fed to the input bias circuit of the input section of the reference charge coupling device 48 as a negative feedback signal. Thus, when the gain of the error amplifier in the comparator 49 is sufficiently high, the two input voltages to the comparator 49 are made equal. That is, the output voltage of the reference charge coupling device 48 is (E1+E2)/2, which is the center voltage of the output voltage dynamic range of the main chare coupling device.
MATSUMOTO SHIYUUZOU
TSUKASAKI HISANOBU
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