Differential amplifier circuit having plural current mirror circuits

1. A device comprising:

first and second input terminals;

first and second power-supply terminals;

a first current path including:

a first node;

a first transistor coupled between the first power-supply terminal and the first node and having a control electrode coupled to the first node; and

a second transistor coupled between the second power-supply terminal and the first node and having a control electrode coupled to the first input terminal;

a second current path including:

a second node;

a third transistor coupled between the first power-supply terminal and the second node and having a control electrode coupled to the second node;

a fourth transistor coupled between the second power-supply terminal and the second node and having a control electrode coupled to the second input terminal; and

a fifth transistor coupled between the first power-supply terminal and the second node and having a control electrode coupled to the first node; and

a first current mirror circuit generating a first output current based on a first input current flowing through the first transistor;

a second current mirror circuit generating a second output current based on a second input current flowing through the third transistor;

a third current mirror circuit generating a third output current based on one of the first and second output currents;

an output node through which a difference current between the other of the first and second output currents and the third output current flows; and

a driver transistor coupled between the first and second power-supply terminals, the driver transistor having a control electrode coupled to the output node.

2. The device as claimed in claim 1 , wherein

a current ratio of the first input current and the first output current is substantially 1:1, and

a current ratio of the second input current and the second output current is k:1, where k<1.

3. The device as claimed in claim 1 , wherein the third current mirror circuit includes fourth and fifth current mirror circuits that are cascode-connected.

4. The device as claimed in claim 1 , wherein one end of the driver transistor is coupled to the first power-supply terminal and the other end of the driver transistor is coupled to one of the first and second input terminals.

5. The device as claimed in claim 4 , wherein the other of the first and second input terminals is supplied with a reference potential.

6. The device as claimed in claim 4 , further comprising a first constant current source coupled between the other end of the driver transistor and the second power-supply terminal.

7. The device as claimed in claim 1 , further comprising a second constant current source provided in common for the first and second current paths, the second constant current source being coupled between the second and fourth transistors and the second power-supply terminal.

8. The device as claimed in claim 1 , wherein the first transistor has substantially the same in size as a sum of a size of the third and fifth transistors.

9. The device as claimed in claim 1 , wherein the first, third, and fifth transistors are MOS transistors of a first conductivity type, and the second and fourth transistors are MOS transistors of a second conductivity type.

10. A device comprising:

first and second transistors coupled to form a differential circuit;

a first current mirror circuit generating first and second currents in response to a third current flowing through the first transistor;

a second current mirror circuit generating a fourth current in response to a fifth current,

a sum of the second and fifth currents flowing through the second transistor; and

a third current mirror circuit including an input node coupled to receive the fifth current and an output node coupled to receive the first current; and

a driver transistor having a control electrode coupled to the output node.

11. The device as claimed in claim 10 , wherein

a current ratio of third and first currents is substantially 1:1,

a current ratio of the third and second currents is 1:1-k, where k<1, and

a current ratio of the fourth and fifth currents is substantially k:1.

12. The device as claimed in claim 11 , wherein a current ratio of the one of the input and output nodes of the third current mirror circuit is substantially 1:1.

13. A method comprising:

generating first and second currents at a first current mirror circuit in response to a third current flowing through a first transistor coupled to a second transistor to form a differential circuit;

generating a fourth current at a second current mirror circuit in response to a fifth input current, where a sum of the second and fifth currents flow through the second transistor; and

providing the fifth current to an input node of a third current mirror having an output node coupled to receive the first current, where the output node is coupled to a control electrode of a driver transistor.

14. The method of claim 13 , wherein

a current ratio of third and first currents is substantially 1:1,

a current ratio of the third and second currents is 1:1-k, where k<1, and

a current ratio of the fourth and fifth currents is substantially k:1.

15. The method of claim 14 , wherein a current ratio of the one of the input and output nodes of the third current mirror circuit is substantially 1:1.