| 摘要 |
PURPOSE:To prevent troubles such as the occurrence of noise, by providing a holding capacitor. CONSTITUTION:An input changeover switch SW-G' is provided for switching a capacitor array part 1' to the buffer amplifier 2 side and the earth side, and this switching is controlled by a control signal generated by a digital input controlling part 3'. An analogue output voltage Vout of the buffer amplifier 2 is applied to a holding capacitor CH to charge the holding capacitor CH to the same voltage as this output voltage, and the holding capacitor CH holds an input voltage of the buffer amplifier 2 in the same voltage as the analogue output voltage when the input changeover switch SW-G' is switched to the earth side. A holding capacitor switch SW-H is provided for switching the holding capacitor CH to the input side or the output side of the buffer amplifier 2; and the switch SW-H is switched to the positive input terminal of the buffer amplifier 2 when the input changeover switch SW-G' is switched to the earth side by said control signal, and the switch SW-H is switched to the output terminal of the buffer amplifier 2 when the switch SW-G' is switched to the input side of the buffer amplifier 2. |
