| 摘要 |
PURPOSE:To obtain a differential variable amplifier circuit with which the effect of the ON resistance of an analog switch can be neglected, by providing the 2nd analog switch means which works in response to the 1st analog switch to a differential amplifier circuit which uses an analog switch for changeover of a gain setting resistance. CONSTITUTION:The effect of the ON resistance of an analog switch can be virtually neglected since the input impedance of an operational amplifier is very high. The amplification degree A is equal to (R2+R3+R4+R5)/R1 in case only a pair of SW1 is kept ON. While A=(R3+R4+R5)/(R1+R2) is satisfied when only a pair of SW2 is kept ON. In such a case, the gain of a differential variable amplifier circuit can be set regardless of the ON resistance of the analog switch. |
