Patent ID: 7279941

Claim:
A voltage-frequency conversion apparatus comprising: a variable current source for charging a capacitor; a current amount adjustment curcuit which has a first resistor for applying a first voltage and a second resistor for applying a second voltage and adjusts the amount of a current from the variable current source to be corresponding to a differential voltage between the first voltage and the second voltage, and a current amount adjustment error amplifier for supplying a current corresponding to the differential voltage between the first voltage and the second voltage to either the first resistor or the second resistor, and to the capacitor; a comparator that compares in level a charging voltage produced at one end of the capacitor and a reference voltage, and generates a frequency signal according to the differential voltage between the first voltage and the second voltage; a discharge circuit that discharges the capacitor according to the comparing result of the comparator when the charging voltage exceeds the reference voltage; and a reference voltage control circuit that, when a resistance of the first resistor or the second resistor varies according to its temperature characteristic, changes the value of the reference voltage according to the variation in the resistance of the first resistor or the second resistor so as to maintain constant a frequency of the frequency signal from the comparator, wherein the reference voltage control circuit comprises: an inversely proportional variable current source that generates a current inversely proportional to the resistance of either the first resistor or the second resistor to which a current corresponding to the differential voltage between the first voltage and the second voltage is supplied, a charge/discharge capacitor, a switch circuit for charging the charge/discharge capacitor only in a first time period with use of a current from the inversely proportional variable current source, then holding a charging voltage of the charge/discharge capacitor only in a second time period and thereafter discharging the charging voltage of the charge/discharge capacitor only in a third time period, a switch control circuit that controls opening and closing of the switch circuit, and an output circuit that outputs the reference voltage from a voltage held across the charge/discharge capacitor.