Differential amplifier circuit

• US 5,990,742 A
• Filed: 05/13/1998
• Issued: 11/23/1999
• Est. Priority Date: 11/26/1997
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Fujitsu Limited
• Inventors: Suzuki, Hisao
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): NGUYEN, KHANH V
• Application Number:
  US09/076,919
• Time in Patent Office: 559 Days
• Field of Search: 330/255, 330/253, 330/257, 330/260
• US Class Current: 330/253
• CPC Class Codes: H03F 3/3001 with field-effect transistors

Abstract

A differential amplifier circuit includes a differential input circuit which receives first and second input signals. The differential input circuit amplifies a potential difference between the input signals and outputs first and second voltage signals at first and second output terminals representing the amplified potential difference. A first output transistor is connected between a high potential power supply and a third output terminal of the differential input circuit. The first output transistor pulls up the potential at the third output terminal. A second output transistor is connected between the third output terminal and a low potential power supply for pulling down the potential at the third output terminal. A gate voltage controller is connected to the first and second output terminals and receives the first and second voltage signals and controls voltages applied to each of the gate terminals of the first and second output transistors to control the currents flowing to them.

Claims

1. A differential amplifier comprising:

a differential input circuit having first and second input terminals for receiving first and second input signals, and amplifying a potential difference between the two input signals, and having first and second output terminals for outputting first and second voltage signals, respectively, the first and second voltage signals representing the amplified potential difference between the two input signals;

a third output terminal for outputting a third output signal of the differential amplifier;

a first output transistor connected between a high potential power supply and the third output terminal for pulling-up a potential at the third output terminal wherein the first output transistor includes a P-channel MOS transistor;

a second output transistor connected between the third output terminal and a low potential power supply for pulling-down the potential at the third output terminal wherein the second output transistor includes an N-channel MOS transistor; and

a gate voltage controller connected to the first and second output terminals for receiving the first and second voltage signals, respectively, and for controlling voltages applied to each of the gate terminals of the first and second output transistors based on the first and second voltage signals to control the currents flowing to the first and second output transistors;

wherein the gate voltage controller applies a voltage level substantially equal to the low potential power supply to the gate terminal of the first output transistor when turning on the first output transistor for pull-up operation, and wherein applies a voltage level substantially equal to the high potential power supply to the gate terminal of the second output transistor when turning on the second output transistor for pull-down operation;

wherein the gate voltage controller applies a voltage that is higher than that of the low potential power supply by a predetermined voltage to the gate terminal of the first output transistor for pull-up operation, and applies a voltage that is lower than that of the high potential power supply by the predetermined voltage to the gate terminal of the second output transistor for pull-down operation;

wherein the predetermined voltage is a source-drain voltage of a MOS transistor at an on-state.

3. The differential amplifier according to claim 1 or 2, wherein the gate voltage controller includes:

a first current controller for receiving the first voltage signal from the first output terminal and outputting a current corresponding to the first voltage signal; and

a first MOS transistor for receiving the second voltage signal from the second output terminal and for outputting a drain current corresponding to the second voltage signal;

wherein the gate terminal of the first output transistor is connected to the first current controller and the first MOS transistor, and a voltage corresponding to a current ratio of an output current of the first current controller to the drain current of the first MOS transistor is applied to the gate terminal of the first output transistor.

4. The differential amplifier according to claim 3, wherein the gate voltage controller includes:

a second MOS transistor having a drain current that is substantially equal to the drain current of the first output transistor; and

a second current controller for receiving the drain current from the second MOS transistor and outputting a current corresponding to the drain current from the second MOS transistor;

wherein the gate terminal of the second output transistor is connected to the second current controller and the second MOS transistor, and a voltage corresponding to a current ratio of an output current of the second current controller to the drain current of the second MOS transistor is applied to the gate terminal of the second output transistor.

5. The differential amplifier according to claim 4, wherein the first current controller includes a current mirror circuit for setting an idling current flowing to the first output transistor based on a bias current of the differential input circuit.

6. The differential amplifier according to claim 4, further comprising a current correction circuit for correcting a current difference between an input current provided to the second current controller and an output current from the first current controller and supplying the second current controller with a current corresponding to the current difference.

7. The differential amplifier according to claim 6, wherein the second current controller includes a current mirror circuit, and wherein the current correction circuit supplies the current mirror circuit of the second current controller with the current corresponding to the current difference.

8. The differential amplifier according to claim 6, wherein the second current controller includes a current mirror circuit, and wherein the current correction circuit absorbs the current corresponding to the current difference from the current mirror circuit of the second current controller.

9. The differential amplifier according to claim 1 or 2, further comprising:

a first MOS transistor connected to the first output terminal; and

a second MOS transistor connected to the second output terminal, wherein the first and second MOS transistors generate an operating current for the differential input circuit.

10. The differential amplifier according to claim 1 or 2, further comprising:

a first current mirror circuit connected to the first and second output terminals and formed as part of the differential input circuit; and

a second current mirror circuit connected to the first and second output terminals and formed as part of the gate voltage controller;

wherein the first and second current mirror circuits form a pair, and generate an operating current for the differential input circuit.

11. The differential amplifier according to claim 10, wherein each of the first and second current mirror circuits includes a pair of transistors.

12. The differential amplifier according to claim 1 or 2, wherein the third output terminal is connected to one of the first and second input terminals.

2. A differential amplifier comprising:

a differential input circuit having first and second input terminals for receiving first and second input signals, and amplifying a potential difference between the two input signals, and having first and second output terminals for outputting first and second voltage signals, respectively, the first and second voltage signals representing the amplified potential difference between the two input signals;

a third output terminal for outputting a third output signal of the differential amplifier;

a first output transistor connected between a high potential power supply and the third output terminal for pulling-up a potential at the third output terminal wherein the first output transistor includes a P-channel MOS transistor;

a second output transistor connected between the third output terminal and a low potential power supply for pulling-down the potential at the third output terminal wherein the second output transistor includes an N-channel MOS transistor; and

a gate voltage controller connected to the first and second output terminals for receiving the first and second voltage signals, respectively, and for controlling voltages applied to each of the gate terminals of the first and second output transistors based on the first and second voltage signals to control the currents flowing to the first and second output transistors;

wherein the gate voltage controller applies a voltage level substantially equal to the low potential power supply to the gate terminal of the first output transistor when turning on the first output transistor for pull-up operation, and wherein applies a voltage level substantially equal to the high potential power supply to the gate terminal of the second output transistor when turning on the second output transistor for pull-down operation,

wherein the gate voltage controller applies a voltage that is higher than that of the low potential power supply by a predetermined voltage to the gate terminal of the second output transistor for pull-up operation, and applies a voltage that is lower than that of the high potential power supply by the predetermined voltage to the gate terminal of the first output transistor for pull-down operation;

wherein the predetermined voltage is a source-drain voltage of a MOS transistor at an on-state.

13. A differential amplifier circuit having first and second input terminals for receiving first and second input signals and an output terminal, comprising:

a current mirror circuit including a first current mirror transistor and a second current mirror transistor, wherein a source of the first and second current mirror transistors is connected to a high potential power supply, a gate of the first current mirror transistor is connected to its drain and to a gate of the second current mirror transistor, and a drain of the first current mirror transistor is connected to a low potential power supply by way of a current source;

a differential input circuit connected to the first and second input terminals for receiving the first and second input signals and amplifying a potential difference between the first and second input signals, and generating first and second voltage signals representing the potential difference, and the differential input circuit connected to the current mirror circuit;

a first output transistor connected between the high potential power supply and the output terminal;

a second output transistor connected between the output terminal and the low potential power supply; and

a gate control voltage controller, connected to the differential input circuit and receiving the first and second voltage signals, for controlling voltages applied to the gates of the first and second output transistors based on the first and second voltage signals to control the currents flowing through the first and second output transistors, wherein the gate voltage controller applies a voltage level substantially equal to the low potential power supply to the gate terminal of the first output transistor when turning on the first output transistor and applies a voltage level substantially equal to the high potential power supply to the gate terminal of the second output transistor when turning on the second output transistor.

14. The differential amplifier circuit of claim 13, wherein the output terminal is connected to the second input terminal.

15. The differential amplifier circuit of claim 13, wherein the differential input circuit is connected to the drain of the second transistor of the current mirror circuit.

16. The differential amplifier circuit of claim 13, wherein the differential input circuit comprises:

a first transistor having its gate connected to the first input terminal for receiving the first input signal;

a second transistor having its gate connected to the second input terminal for receiving the second input signal, and its source connected to the source of the first transistor;

a third transistor connected between the first transistor and the low potential power supply, a gate of the third transistor being connected to its drain and to the drain of the first transistor; and

a fourth transistor connected between the second transistor and the low potential power supply, a gate of the fourth transistor being connected to the gate of the third transistor and to the drain of the second transistor, wherein the first voltage signal is provided from a first node between the drains of the first and third transistors, the second voltage signal is provided from a second node between the drains of the second and fourth transistors, and a third output signal is provided to the current mirror circuit from a node between the source of the first and second transistors.

17. The differential amplifier circuit of claim 13, wherein the differential input circuit comprises:

a first transistor having its gate connected to the first input terminal for receiving the first input signal;

a second transistor having its gate connected to the second input terminal for receiving the second input signal, and its source connected to the source of the first transistor;

a third transistor connected between the first transistor and the low potential power supply, a gate of the third transistor being connected to its drain and to the drain of the first transistor; and

a fourth transistor connected between the second transistor and the low potential power supply, a gate of the fourth transistor being connected to its drain and to the drain of the second transistor, wherein the first voltage signal is provided from a first node between the drains of the first and third transistors, the second voltage signal is provided from a second node between the drains of the second and fourth transistors, and a third output signal is provided to the current mirror circuit from a node between the source of the first and second transistors.

18. The differential amplifier circuit of claim 13, wherein the gate voltage controller comprises:

a first current control circuit receiving the first voltage signal;

a second current control circuit connected to the first current control circuit;

a first transistor connected between the first current control circuit and the second current control circuit; and

a second transistor connected between the first current control circuit and the low potential power supply, a first node being defined at a connection of the drain of the second transistor, the first current control circuit and the gate of the first transistor, and a second node being defined at a connection between the first and second current control circuits, wherein a first gate control signal is provided for controlling the gate of the first output transistor and a second gate control signal is provided for controlling the gate of the second output transistor, the first gate control signal being provided from the first node and the second gate control signal being provided from the second node.

19. The differential amplifier circuit of claim 18, wherein the second current control circuit comprises:

a first transistor connected between the first current control circuit and the low potential power supply; and

a second transistor connected between the first transistor of the gate voltage controller and the low potential power supply, wherein the gates of the first and second transistors of the second current control circuit are connected together and to the drain of the second transistor.

20. The differential amplifier circuit of claim 19, wherein the first current control circuit comprises:

a first transistor having a gate connected to the differential input circuit and receiving the first voltage signal and a source connected to the low potential power supply;

a second transistor having a source connected to the high potential power supply, a drain connected to the drain of the first transistor of the first current control circuit, and a gate connected to its drain and to the drain of the first transistor;

a third transistor having a source connected to the high potential power supply, a gate connected to the gate of the second transistor, and a drain connected to the drain of the second transistor of the gate voltage controller; and

a fourth transistor having a source connected to the high potential power supply, a gate connected to the drains of the first and second transistors of the first current control circuit, and a drain connected to the gate of the second output transistor.

21. The differential amplifier circuit of claim 13, wherein the differential input circuit comprises:

a first transistor having its gate connected to the first input terminal for receiving the first input signal;

a second transistor having its gate connected to the second input terminal for receiving the second input signal, and its source connected to the source of the first transistor;

a third transistor connected between the first transistor and the low potential power supply, a gate of the third transistor being connected to its drain and to the drain of the first transistor;

a fourth transistor connected between the second transistor and the low potential power supply, a gate of the fourth transistor being connected to its drain and to the drain of the second transistor;

a fifth transistor connected between the second transistor and the low potential power supply, a gate of the fifth transistor being connected to the gate of the third transistor; and

a sixth transistor connected between the first transistor and the low potential power supply, a gate of the sixth transistor being connected to the gate of the fourth transistor, wherein the first voltage signal is provided from a first node at a connection of the drains of the first, third and sixth transistors, the second voltage signal is provided from a second node at a connection of the drains of the second, fourth and fifth transistors, and a third output signal is provided to the current mirror circuit from a third node at a connection of the sources of the first and second transistors.

22. The differential amplifier circuit of claim 13, further comprising:

a differential current detector circuit;

a first transistor, connected between the high potential power supply and the differential current detector circuit, having a gate connected to the gate voltage controller; and

a second transistor, connected between the high potential power supply and the differential current detector circuit, having a gate connected to the gate of the first output transistor, wherein the differential current detection circuit detects a difference between the drain currents from the first and second transistors and feeds a differential current to the differential input circuit, thereby allowing for a maximum source current at the output terminal of the differential amplifier circuit.