Differential amplifier circuit

• US 8,207,789 B2
• Filed: 03/23/2011
• Issued: 06/26/2012
• Est. Priority Date: 03/29/2010
• Status: Active Grant

• Current Assignee: Ablic Inc. (MinebeaMitsumi Inc.)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Tsuzaki, Toshiyuki
• Primary Examiner(s): Choe, Henry
• Application Number:
  US13/070,151
• Publication Number:
  US 20110234319A1
• Time in Patent Office: 461 Days
• Field of Search: 330/253, 330/255, 330/257, 330/261
• US Class Current: 330/253
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence

Abstract

Provided is a differential amplifier circuit with a small circuit size. When a differential voltage (Vinp−Vinn) is higher than a predetermined voltage, a PMOS transistor (4) is turned ON. At this time, a current source (12) is connected in parallel to a current source (11), and the current source (12) supplies a drive current to a differential amplifier circuit (10). In other words, the current sources (11 and 12), rather than only the current source (11), supply a total current (I11+I12) to the differential amplifier circuit (10) as the drive current. Accordingly, a slew rate of an output voltage (Vout) is increased. Two PMOS transistors and the current source (12) are simply required for controlling the slew rate of the output voltage (Vout), and hence the differential amplifier circuit (10) is small in circuit size.

Claims

1. A differential amplifier circuit, comprising:

a current mirror circuit which includes a first terminal and a second terminal and is provided to a first power supply terminal;

a first current source provided between a first node and a second power supply terminal;

a first transistor of second conductivity type, including a gate connected to a second input terminal, a source connected to the first node, and a drain connected to the first terminal of the current mirror circuit;

a second transistor of the second conductivity type, including a gate connected to a first input terminal, a source connected to the first node, and a drain connected to the second terminal of the current mirror circuit;

a second current source;

a first transistor of first conductivity type, including a gate connected to the second input terminal, a source connected to the first node, and a drain connected to the second power supply terminal via the second current source; and

a second transistor of the first conductivity type, including a gate connected to the first input terminal, a source connected to the first node, and a drain connected to the second power supply terminal via the second current source.

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

a third current source;

a third transistor of the first conductivity type, including a gate connected to the second input terminal, a source connected to the first node, and a drain connected to the second power supply terminal via the third current source, the third transistor having a threshold voltage different from threshold voltages of the first transistor of the first conductivity type and the second transistor of the first conductivity type; and

a fourth transistor of the first conductivity type, including a gate connected to the first input terminal, a source connected to the first node, and a drain connected to the second power supply terminal via the third current source, the fourth transistor having a threshold voltage different from the threshold voltages of the first transistor of the first conductivity type and the second transistor of the first conductivity type.

3. The differential amplifier circuit according to claim 1, wherein the current mirror circuit further comprises:

a fifth transistor of the first conductivity type, including a source connected to the first power supply terminal and a drain connected to the first terminal of the current mirror circuit; and

a sixth transistor of the first conductivity type, including a gate connected to a gate and the drain of the fifth transistor of the first conductivity type and to the first terminal of the current mirror circuit, a source connected to the first power supply terminal, and a drain connected to the second terminal of the current mirror circuit.

4. The differential amplifier circuit according to claim 2, wherein the current mirror circuit further comprises:

a fifth transistor of the first conductivity type, including a source connected to the first power supply terminal and a drain connected to the first terminal of the current mirror circuit; and

a sixth transistor of the first conductivity type, including a gate connected to a gate and the drain of the fifth transistor of the first conductivity type and to the first terminal of the current mirror circuit, a source connected to the first power supply terminal, and a drain connected to the second terminal of the current mirror circuit.

5. The differential amplifier circuit according to claim 3, wherein the first transistor of the first conductivity type and the second transistor of the first conductivity type each have a threshold voltage different from threshold voltages of the fifth transistor of the first conductivity type and the sixth transistor of the first conductivity type.

6. The differential amplifier circuit according to claim 4, wherein the first transistor of the first conductivity type and the second transistor of the first conductivity type each have a threshold voltage different from threshold voltages of the fifth transistor of the first conductivity type and the sixth transistor of the first conductivity type.