Offset fixing operational amplifier circuit

1. An offset fixing operational amplifier circuit comprising:

an operational amplifier circuit including an input stage containing a first constant current source, a second constant current source, a first differential pair and a second differential pair;

a bias circuit for supplying a bias voltage to the operational amplifier circuit; and

an offset fixing circuit for controlling the input stage in accordance with an input voltage of the operational amplifier circuit;

wherein the offset fixing circuit includes:

a first switch for turning on/off the first constant current source;

a second switch for turning on/off the second constant current source;

a voltage generator for determining transition timing of a control signal used for controlling the first switch and the second switch; and

a voltage comparator for generating the control signal on the basis of an input voltage of a noninverted input terminal of the operational amplifier circuit and an output voltage of the voltage generator.

2. An offset fixing operational amplifier circuit comprising:

an operational amplifier circuit including an input stage containing a first constant current source, a second constant current source, a first differential pair and a second differential pair;

a bias circuit for supplying a bias voltage to the operational amplifier circuit; and

an offset fixing circuit for controlling the input stage in accordance with an input voltage of the operational amplifier circuit;

wherein the offset fixing circuit includes:

a first switch for turning on/off a noninverted input of the first differential pair;

a second switch for turning on/off an inverted input of the first differential pair;

a third switch for tuning on/off a noninverted input of the second differential pair;

a fourth switch for turning on/off an inverted input of the second differential pair;

a voltage generator for determining transition timing of a control signal used for controlling the first, second, third and fourth switches; and

a voltage comparator for generating the control signal on the basis of an input voltage of a noninverted input terminal of the operational amplifier circuit and an output voltage of the voltage generator.

3. The offset fixing operational amplifier circuit of claim 2 ,

wherein the offset fixing circuit further includes:

a third constant current source connected in parallel to the first constant current source;

a fifth switch for turning on/off the third constant current source;

a fourth constant current source connected in parallel to the second constant current source; and

a sixth switch for turning on/off the fourth constant current source, and

the control signal is used for controlling the first, second, third, fourth, fifth and sixth switches.

4. The offset fixing operational amplifier circuit of claim 3 ,

wherein the offset fixing circuit further includes:

a first current regulator circuit capable of arbitrarily regulating a current value of the third constant current source; and

a second current regulator circuit capable of arbitrarily regulating a current value of the fourth constant current source.

5. The offset fixing operational amplifier circuit of claim 1 ,

wherein the offset fixing circuit further includes a voltage regulator circuit capable of arbitrarily regulating the output voltage of the voltage generator.

6. The offset fixing operational amplifier circuit of claim 2 ,

wherein the offset fixing circuit further includes a voltage regulator circuit capable of arbitrarily regulating the output voltage of the voltage generator.

7. The offset fixing operational amplifier circuit of claim 1 further comprising, a bias voltage regulator circuit capable of arbitrarily regulating the bias voltage.

8. A D/A converter comprising:

an offset fixing operational amplifier comprising:

an operational amplifier circuit including an input stage containing a first constant current source, a second constant current source, a first differential pair and a second differential pair;

a bias circuit for supplying a bias voltage to the operational amplifier circuit; and

an offset fixing circuit for controlling the input stage in accordance with an input voltage of the operational amplifier circuit;

a voltage generator for generating a plurality of voltages; and

a selector for selecting one of the plurality of voltages in accordance with a data signal of a plurality of bits input thereto and inputting the selected voltage to the operational amplifier circuit,

the offset fixing circuit including:

a first switch for tuning on/off the first constant current source; and

a second switch for turning on/off the second constant current source,

the first switch and the second switch being controlled in accordance with the data signal.

9. A D/A converter comprising:

an offset fixing operational amplifier comprising:

an operational amplifier circuit including an input stage containing a first constant current source, a second constant current source, a first differential pair and a second differential pair;

a bias circuit for supplying a bias voltage to the operational amplifier circuit; and

an offset fixing circuit for controlling the input stage in accordance with an input voltage of the operational amplifier circuit;

a voltage generator for generating a plurality of voltages; and

a selector for selecting one of the plurality of voltages in accordance with a data signal of a plurality of bits input thereto and inputting the selected voltage to the operational amplifier circuit,

the offset fixing circuit including:

a first switch for tuning on/off an inverted input of the second differential pair; and

a second switch for turning on/off a noninverted input of the second differential pair,

the first switch and the second switch being controlled in accordance with the data signal.