Circuit for generating identical output currents

• US 7,436,248 B2
• Filed: 04/19/2006
• Issued: 10/14/2008
• Est. Priority Date: 05/06/2005
• Status: Expired due to Fees

• Current Assignee: Oki Semiconductor Company Limited (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Furuichi, Shuji
• Primary Examiner(s): Wells; Kenneth B.
• Assistant Examiner(s): Hiltunen; Thomas J
• Application Number:
  US11/406,460
• Publication Number:
  US 20060261863A1
• Time in Patent Office: 909 Days
• Field of Search: 327/530, 327/538, 327540-543, 323312-317
• US Class Current: 327/543
• CPC Class Codes: G05F 3/262 using field-effect transistors only
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

A current driving circuit includes a bias voltage generator that generates a bias voltage and multiple constant current drivers that output driving currents. Each constant current driver includes first and second transistors coupled in series between two power supply potentials, and a third transistor that forms a current mirror with the second transistor. The control terminal of the first transistor receives the bias voltage. The control terminals of the second and third transistors are both connected to the node at which the first and second transistors are interconnected. This circuit configuration makes the output current, which is obtained from the third transistor, comparatively immune to fabrication process variations and variations in power-supply potentials.

Claims

1. A current driving circuit supplied with power having a first potential and a second potential and receiving a reference voltage, the current driving circuit having a bias voltage generator and a plurality of constant current drivers, the bias voltage generator receiving the reference voltage, generating a bias voltage, and using the bias voltage to regulate a reference current, the constant current drivers receiving the bias voltage and outputting driving currents related to the reference current, wherein each constant current driver comprises:

a first node;

a first transistor of a first conductive type, having a first main electrode receiving the first potential, a second main electrode connected to the first node, and a control terminal receiving the bias voltage;

a second transistor of a second conductive type, having a first main electrode receiving the second potential, a second main electrode connected to the first node, and a control terminal connected to the first node; and

a third transistor of the second conductive type, having a first main electrode receiving the second potential, a second main electrode outputting one of the driving currents, and a control terminal connected to the first node,

wherein the bias voltage generator comprises;

a second node;

a third node;

an operational amplifier having a non-inverting input terminal receiving the reference voltage, an inverting input terminal connected to the second node, and an output terminal outputting the bias voltage;

a fourth transistor of the first conductive type, having a first main electrode receiving the first potential, a second main electrode connected to the third node, and a control terminal connected to the output terminal of the operational amplifier;

a fifth transistor of the second conduetive type, having a first main electrode receiving the second potential, a second main electrode connected to the third node, and a control terminal connected to the third node;

a sixth transistor of the first conductive type, having a first main electrode receiving the second potential, a second main electrode connected to the second node, and a control terminal connected to the third node; and

a resistor having one terminal connected to the second node and another terminal receiving the first potential.

2. The current driving circuit of claim 1, wherein the first and fourth transistors have mutually identical dimensions and are formed simultaneously under identical processing conditions, the second and fifth transistors have mutually identical dimensions, the third and sixth transistors have mutually identical dimensions, and the second, third, fifth, and sixth transistors are formed simultaneously under identical processing conditions.

3. The current driving circuit of claim 1, wherein the bias voltage generator further comprises a seventh transistor of the second conductive type for supplying the second potential to the fifth and sixth transistors, the seventh transistor having a first main electrode receiving the second potential, a second main electrode connected to the first main electrodes of the fifth and sixth transistors, and a control electrode receiving the first potential.

4. The current driving circuit of claim 1, wherein the fourth, fifth, and sixth transistors are field-effect transistors.

5. The current driving circuit of claim 4, wherein the fourth transistor is an NMOS transistor, and the fifth and sixth transistors are PMOS transistors.

6. The current driving circuit of claim 4, wherein the fourth transistor is a PMOS transistor, and the fifth and sixth transistors are NMOS transistors.