Patent ID: 7262640

Claim:
A voltage-frequency conversion apparatus having: a variable current source for charging a capacitor; a current amount adjustment unit that adjusts a current amount of the variable current source for charging the capacitor to be corresponding to a differential voltage between a first voltage and a second voltage; a comparator that compares in level a charging voltage produced at one end of the capacitor and a reference voltage; a discharge unit that discharges the charging voltage of the capacitor according to the comparison result of the comparator when the charging voltage exceeds the reference voltage; and a reference voltage fluctuation unit that makes the reference voltage fluctuate periodically within a predetermined voltage range, wherein the reference voltage fluctuation unit includes: a first voltage source for generating a voltage V 1 , a second voltage source for generating a voltage V 2 smaller in voltage value than the voltage V 1 , a first capacitor, a second capacitor with a capacitance smaller than that of the first capacitor, a first switch circuit for charging the first capacitor by units depending on a capacitance of the second capacitor so that its voltage ascends from the voltage V 2 side to the voltage V 1 side, a second switch circuit for discharging the first capacitor by units depending on the capacitance of the second capacitor so that its voltage descends from the voltage V 1 side to the voltage V 2 side, and a timing control circuit that controls switch timings of the first switch circuit and the second switch circuit, wherein a charging/discharging voltage occurring at one end of the first capacitor is applied as the reference voltage to the comparator, wherein a frequency signal is generated from the comparator corresponding to the differential voltage between the first voltage and the second voltage, and wherein the reference voltage is a voltage with a stepwise waveform ascending and descending repeatedly at a cycle.