Push-pull amplifier circuit and operational amplifier circuit using the same

1. A push-pull amplifier circuit comprising first, second, and third current paths,

wherein the first current path includes a first transistor that allows a first current to flow through the first current path according to an input signal,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current;

a first resistor; and

a third transistor that has a control terminal directly connected to the first resistor, and

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that is connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current.

2. The push-pull amplifier circuit according to claim 1 , further comprising a constant current source connected between the third transistor and a ground voltage terminal.

3. A push-pull amplifier circuit comprising:

first, second, and third current paths; and

at least one of a first, second, and third capacitor elements,

wherein the first current path includes a first transistor that allows a first current to flow through the first current path according to an input signal,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current:

a first resistor; and

a third transistor that is connected to one end of the first resistor and has a control terminal connected to an other end of the first resistor,

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current,

wherein the first capacitor element is connected between an input terminal and the output terminal, the input terminal receiving the input signal,

wherein the second capacitor element is connected between the first node and the output terminal, and

wherein the third capacitor element is connected in parallel with the first resistor.

4. A push-pull amplifier circuit comprising:

first, second, and third current paths,

wherein the first current path is connected between a first power supply terminal and a second power supply terminal, and the first current path includes:

a first transistor that allows a first current to flow through the first current path according to an input signal;

a sixth transistor; and

a first constant current source,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current;

a first resistor; and

a third transistor that is connected to one end of the first resistor and has a control terminal connected to an other end of the first resistor,

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that is connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current,

wherein the first and sixth transistors are connected in parallel between the first power supply terminal and a second node,

wherein control terminals of the second and sixth transistors are each connected to the second node, and

wherein the first constant current source is connected between the second node and the second power supply terminal.

5. The push-pull amplifier circuit according to claim 4 , wherein the second current path is connected between the first power supply terminal and the second power supply terminal, and further includes a second constant current source,

wherein the second transistor is connected between the first power supply terminal and a third node, and has a control terminal connected to the second node,

wherein the other end of the first resistor is connected to the third node, and

wherein the second constant current source is connected between the second power supply terminal and the third transistor.

6. The push-pull amplifier circuit according to claim 5 , wherein a value of a voltage drop at both ends of the first resistor is substantially equal to a value of a voltage difference between both ends of the second constant current source when the second constant current source allows the second current to flow.

7. The push-pull amplifier circuit according to claim 5 , further comprising a bias voltage generation circuit that includes a second resistor and a seventh transistor, the second resistor and the seventh resistor being connected in series between the first and second power supply terminals,

wherein the seventh transistor has a control terminal connected to a fourth node between the second resistor and the seventh transistor, and

wherein current values output from the first and second constant current sources are determined according to a voltage of the fourth node.

8. The push-pull amplifier circuit according to claim 7 , wherein the first and second constant current sources include eighth and ninth transistors, respectively, and

wherein control terminals of the eighth and ninth transistors are each connected to the fourth node.

9. The push-pull amplifier circuit according to claim 5 , further comprising a bias voltage generation circuit that comprises:

a second resistor;

a third resistor;

a seventh transistor; and

a tenth transistor, the second and third resistors and the seventh and tenth transistors being connected in series between the first and second power supply terminals,

wherein the third resistor is connected between the first power supply terminal and a fifth node,

wherein the second resistor is connected between the fifth node and a fourth node,

wherein the tenth transistor is connected between the fourth node and a sixth node,

wherein the seventh transistor is connected between the sixth node and the second power supply terminal,

wherein the tenth transistor has a control terminal connected to the fifth node,

wherein the seventh transistor has a control terminal connected to the fourth node, and

wherein current values output from the first and second constant current sources are determined according to a voltage of the fourth node.

10. The push-pull amplifier circuit according to claim 9 , wherein the first constant current source includes an eighth transistor,

wherein the second constant current source includes a ninth transistor, and

wherein control terminals of the eighth and ninth transistors are each connected to the fourth node.

11. The push-pull amplifier circuit according to claim 10 , wherein a resistance ratio between the second resistor and the first resistor is substantially equal to a transistor size ratio between the ninth transistor and the seventh transistor.

12. A push-pull amplifier circuit comprising first, second, and third current paths that are connected between a first power supply terminal and a second power supply terminal,

wherein the first current path includes:

a first transistor that allows a first current to flow through the first current path according to an input signal; and

an eleventh transistor connected in series with the first transistor,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current;

a first resistor; and

a third transistor that is connected to one end of the first resistor and has a control terminal connected to an other end of the first resistor; and

first and second constant current sources connected in series with the first resistor and the third transistor, and the second transistor connected in parallel with the second constant current source,

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that is connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current,

wherein the eleventh transistor has a control terminal connected to a seventh node between the first transistor and the eleventh transistor,

wherein the first constant current source is connected between the first power supply terminal and the other end of the first resistor,

wherein the second constant current source is connected between the third transistor and the second power supply terminal, and

wherein the second transistor has a control terminal connected to the seventh node.

13. The push-pull amplifier circuit according to claim 12 , further comprising a bias voltage generation circuit that includes a second resistor and a seventh transistor, the second resistor and the seventh transistor being connected in series between the first and second power supply terminals,

wherein the seventh transistor has a control terminal connected to a fourth node between the second resistor and the seventh transistor, and

wherein a current value output from the second constant current source is determined according to a voltage of the fourth node.

14. The push-pull amplifier circuit according to claim 13 , wherein the second constant current source includes a ninth transistor, and

wherein the ninth transistor has a control terminal connected to the fourth node.

15. The push-pull amplifier circuit according to claim 12 , further comprising a bias voltage generation circuit that includes second and third resistors and seventh and tenth transistors, the second and third resistors and the seventh and tenth transistors being connected in series between the first and second power supply terminals,

wherein the third resistor is connected between the first power supply terminal and a fifth node,

wherein the second resistor is connected between the fifth node and a fourth node,

wherein the tenth transistor is connected between the fourth node and a sixth node,

wherein the seventh transistor is connected between the sixth node and the second power supply terminal,

wherein the tenth transistor has a control terminal connected to the fifth node,

wherein the seventh transistor has a control terminal connected to the fourth node, and

wherein a current value output from the second constant current source is determined according to a voltage of the fourth node.

16. The push-pull amplifier circuit according to claim 15 , wherein the second constant current source includes a ninth transistor, and

wherein the ninth transistor has a control terminal connected to the fourth node.

17. The push-pull amplifier circuit according to claim 16 , wherein a resistance ratio between the second resistor and the first resistor is substantially equal to a transistor size ratio between the ninth transistor and the seventh transistor.

18. A push-pull amplifier circuit comprising first, second, and third current paths,

wherein the first current path includes a first transistor that allows a first current to flow through the first current path according to an input signal,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current;

a first resistor; and

a third transistor that is connected to one end of the first resistor and has a control terminal connected to an other end of the first resistor,

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that is connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current, and

wherein an operational amplifier circuit is formed by connecting an output terminal of a differential amplifier circuit that outputs an output signal according to a differential input signal, with an input terminal that receives the input signal of the push-pull amplifier circuit.

19. An operational amplifier circuit comprising:

a push-pull amplifier circuit comprising first, second, and third current paths; and

a differential amplifier circuit that outputs an output signal according to a differential input signal,

wherein the first current path includes a first transistor that allows a first current to flow through the first current path according to an input signal,

wherein the second current path includes:

a second transistor that allows a second current to flow through the second current path according to the first current, the second current having a phase opposite to a phase of the first current;

a first resistor; and

a third transistor that is connected to one end of the first resistor and has a control terminal connected to an other end of the first resistor,

wherein the third current path includes:

an output terminal;

a fourth transistor that is connected to the output terminal and allows a current to flow through the third current path according to the input signal, the current having a same phase as the first current; and

a fifth transistor that is connected to the output terminal and allows a current to flow through the third current path according to a voltage of a first node between the first resistor and the third transistor, the current having the same phase as the second current, and

wherein an input terminal that receives the input signal of the push-pull amplifier circuit is connected with an output terminal of the differential amplifier circuit.