| 摘要 |
PROBLEM TO BE SOLVED: To surely compensate a DC offset voltage or a wide frequency. SOLUTION: Differential amplifier circuits 41, 43, 44 are connected in cascade through DC couplings. A smoothing circuit 51 smoothes a noninverting amplified signal outputted at a terminal P4 by using a smoothing resistor R17 and a smoothing capacitor C11, provides an output of a mean DC voltage Vp4 of the noninverting amplified signal to a terminal D as a detected voltage Vd and smoothes an inverting amplified signal outputted at a terminal rP4 by using a smoothing resistor R18 and the smoothing capacitor C11, provides an output of a mean DC voltage Vrp4 of the inverting amplified signal to a terminal rD as a detected voltage Vrd. A DC compensation circuit 52 applies differential adjustment to compensation currents Ic, Irc, so that the voltages Vp4 and Vrp4 are equal to each other to compensate for the DC offset voltage. For example, in the case of Vp4>Vrp4 (Vd>Vrd), the current Ic is increased to decrease the mean DC voltage Vp1 at the terminal P1 and to decrease the Irc, thereby increasing the mean DC voltage Vrp1 at the terminal rP1. |
