Variable reference voltage source

1. A variable reference voltage source that generates a variable reference voltage corresponding to setting data set from outside, the variable reference voltage source comprising:

a control unit including a calibration control unit that controls operation for calibrating an offset and a predetermined unit voltage inside the variable reference voltage source and an output control unit that controls operation for outputting the variable reference voltage;

a reference voltage unit that outputs a reference voltage; and

an integrated-voltage generating unit that repeats, when the calibration control unit controls the operation, an integrating operation until an integrated voltage obtained by integrating the predetermined unit voltage becomes equal to the reference voltage and outputs, when the output control unit controls the operation, the variable reference voltage corresponding to the setting data,

wherein the integrated-voltage generating unit includes:

a fourth switch that changes magnitude of the unit voltage to a same voltage as the reference voltage or intermediate potential smaller than the reference voltage;

a second crossbar switch that determines polarity of the unit voltage;

an integrating unit that generate an integrated voltage obtained by integrating the unit voltage;

a determiner that determines which of the reference voltage and the integrated voltage is larger; and

a first crossbar switch that switches connection between when the reference voltage is input to one input of the determiner and the integrated voltage is input to another input of the determiner and when the integrated voltage is input to the one input of the determiner and the reference voltage is input to the other input of the determiner.

2. The variable reference voltage source according to claim 1 , wherein the integrating unit includes:

an operational amplifier;

a first capacitor charged by the unit voltage;

a second capacitor that holds an integrated voltage obtained by integrating the unit voltage;

a first switch that switches a voltage of a positive input of the operational amplifier;

a second switch that, when one terminal of the first capacitor is connected to a negative input of the operational amplifier, connects another terminal of the first capacitor to ground potential; and

a third switch that short-circuits both ends of the second capacitor.

3. The variable reference voltage source according to claim 2 , wherein the calibration control unit includes:

an offset-polarity-determination processing unit that determines polarity of an offset voltage of the determiner;

an offset-measurement processing unit that calculates a number of times of integration of a unit voltage equivalent to a sum of offset voltages of the operational amplifier and the determiner;

an intermediate-potential-measurement processing unit that, when a bias voltage of the integrating unit is set to intermediate potential smaller than a reference voltage of the reference voltage unit, calculates a number of times of integration of the unit voltage until an output of the determiner is inverted; and

an integration-unit-measurement processing unit that generates an offset integrated voltage obtained by causing the integrating unit to integrate a unit voltage including an offset voltage of the operational amplifier, causes the determiner to perform comparison of the offset integrated voltage and the reference voltage and acquires a number of times of integration.

4. A variable reference voltage source that generates a variable reference voltage corresponding to setting data set from outside, the variable reference voltage source comprising:

a control unit including a calibration control unit that controls operation for calibrating an offset and a predetermined unit voltage inside the variable reference voltage source and an output control unit that controls operation for outputting the variable reference voltage;

a reference voltage unit that outputs a reference voltage; and

an integrated-voltage generating unit that repeats, when the calibration control unit controls the operation, an integrating operation until an integrated voltage obtained by integrating the predetermined unit voltage becomes equal to the reference voltage and outputs, when the output control unit controls the operation, the variable reference voltage corresponding to the setting data,

wherein the integrated-voltage generating unit includes:

an integrating unit that generates an integrated voltage obtained by integrating the unit voltage;

a determiner that determines which of the reference voltage and the integrated voltage is larger; and

a first crossbar switch that switches connection between when the reference voltage is input to one input of the determiner and the integrated voltage is input to another input of the determiner and when the integrated voltage is input to the one input of the determiner and the reference voltage is input to the other input of the determiner,

the integrating unit includes:

an operational amplifier including positive and negative two kinds of inputs;

a first capacitor charged by the unit voltage;

a second capacitor that holds an integrated voltage obtained by integrating the unit voltage;

a fifth switch that connects the reference voltage and the first capacitor when the first capacitor is charged and connects the first capacitor and a positive input of the operational amplifier when the second capacitor is charged;

a fourth switch that causes the operational amplifier to operate as a unity gain buffer when one terminal of the first capacitor is connected to a negative input of the operational amplifier; and

a third switch that short-circuits both ends of the second capacitor, and

the calibration control unit includes:

an offset-cancel-integration-unit-measurement processing unit that generates an integrated voltage obtained by causing the integrating unit to integrate the unit voltage from which an offset voltage of the operational amplifier is removed, performs comparison of the integration voltage and the reference voltage by switching connection of the first crossbar switch, and acquires a first number of times of offset cancel integration and a second number of times of offset cancel integration; and

an integration-unit-measurement processing unit that generates an offset integrated voltage obtained by causing the integrating unit to integrate the unit voltage including the offset voltage of the operational amplifier and causes the determiner to perform comparison of the offset integrated voltage and the reference voltage and acquires a number of times of integration.

5. The variable reference voltage source according to claim 4 , wherein

the integrated-voltage generating unit further includes:

a voltage generating unit that generates two kinds of intermediate potentials obtained by dividing the reference voltage; and

a determination-voltage switching unit that, when the calibration control unit controls the operation, switches a voltage serving as a reference applied to the determiner via the first crossbar switch to the intermediate potential on a high-potential side or the reference voltage,

the integrating unit further includes:

a sixth switch that connects one of the reference voltage or the intermediate potential on the high-potential side and a terminal of the first capacitor when the first capacitor is charged and connects another of the reference voltage or the intermediate potential on the high-potential side and the terminal of the first capacitor when the second capacitor is charged; and

the output control unit includes:

a positive-offset-cancel-integration processing unit that, when a voltage higher than the intermediate potential on a low-potential side is output based on the setting data, executes processing for connecting the reference voltage and the terminal of the first capacitor when the first capacitor is charged and connecting the intermediate potential on the high-potential side and the terminal of the first capacitor when the second capacitor is charged; and

a negative-offset-cancel-integration processing unit that, when a voltage lower than the intermediate potential on the low-potential side is output based on the setting data, executes processing for connecting the intermediate potential on the high-potential side and the terminal of the first capacitor when the first capacitor is charged and connecting the reference voltage and the terminal of the first capacitor when the second capacitor is charged.

6. A variable reference voltage source that generates a variable reference voltage corresponding to setting data set from outside, the variable reference voltage source comprising:

a control unit including a calibration control unit that controls operation for calibrating an offset and a predetermined unit voltage inside the variable reference voltage source and an output control unit that controls operation for outputting the variable reference voltage;

a reference voltage unit that outputs a reference voltage; and

an integrated-voltage generating unit that repeats, when the calibration control unit controls the operation, an integrating operation until an integrated voltage obtained by integrating the predetermined unit voltage becomes equal to the reference voltage and outputs, when the output control unit controls the operation, the variable reference voltage corresponding to the setting data,

wherein the integrated-voltage generating unit includes:

an integrating unit that generates an integrated voltage obtained by integrating the unit voltage;

a determiner that determines which of the reference voltage and the integrated voltage is larger; and

a first crossbar switch that switches connection between when the reference voltage is input to one input of the determiner and the integrated voltage is input to another input of the determiner and when the integrated voltage is input to the one input of the determiner and the reference voltage is input to the other input of the determiner, and

the integrating unit includes:

a current source;

a sixth switch that connects both ends of a unit capacitor;

a fifth switch that repeatedly connects the current source and the unit capacitor; and

a seventh switch that connects the reference voltage to one terminal of the unit capacitor connected to the fifth switch.