| 摘要 |
PURPOSE:To make a differential amplifier circuit low off-set by making the differential amplifier circuit unbalanced state by a variable impedance device, and controlling a variable impedance device in the direction to correct it. CONSTITUTION:The differential amplifier Amp consists of MOSFETQ2, Q3, an FETQ1 that makes constant current operation, FETQ4, Q6 of load circuit in form of a current mirror, FETQ5, Q7 as variable impedance devices to make off-set cancel and capacitors C1, C2. Reference voltage Vref and an input signal IN are changed-over by a switch SW and inputted to non-inversion input + of the Amp, Amp output and Vref are inputted to a voltage comparator VC, and output of VC becomes a control signal of a control circuit PC that outputs timing signals CK1-CK3 for off-set cancel. After charging C1 by the signal CK1 and making impedance of Q5 lower than that of Q7, C2 is charged by CK2, and off-set of Amp is canceled, and thus, low off-set is realized.
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