| 摘要 |
PURPOSE:To keep an excellent characteristic in response to a battery voltage just before the exhaustion of the service life of the battery source by changing an integration current in response to the level of a power voltage and increasing the conversion gain when the power voltage is high and decreasing the gain when low. CONSTITUTION:Since weighted constant current sources 10, 20 are provided in a buffer amplifier 7, a power voltage dependancy is provided to a reference power supply being a reference of the current source, that is, a post-stage circuit of a transistor (TR) 22 shown in figure. In applying voltage-current conversion to a power voltage 1 by resistors 4, 5 a current having the voltage dependancy is obtained, in order to evade the superimposition power ripple noise onto a reference current, a voltage obtained by inserting an LPF for stabilization to the division of the power supply is connected to the base of the TR 22, a resistor 23 is inserted between the emitter and the power supply terminal to decide a current and a current flowing to the collector is used as the reference current. Thus, the reference current in response to the power voltage is obtained without ripple noise and the conversion gain of the D/A conversion is changed in response to the power voltage.
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