摘要 |
<p>PURPOSE:To achieve a highly accurate switch over of range with an analog switch control with A/D conversion IC by adding another signal line to an input pad section. CONSTITUTION:When measuring a voltage, the input impedance R1 which is indicated by R1 is normally about 10MOMEGA and the voltage is damped by a resistance division of the R1, R2 and R3. This voltage is inputted into a buffer amplifier OP, through resistances for electrostatic control RP2 and RP3 connected to input pads P2 and P3 and input changeover analog switches S3 and S4. With such an arrangement, resistances RP1, RP2 and RP3 for electrostatic control of pads P1-P3 and an ON resistance of the analog switches S1 and S2 are applied to the resistance R1 and won't affect the resistances R2 and R3 for damping voltage. This enables a highly accurate damping of an input signal within an accuracy of an external resistance.</p> |