Constant current driver with auto-clamped pre-charge function

• US 6,323,631 B1
• Filed: 01/18/2001
• Issued: 11/27/2001
• Est. Priority Date: 01/18/2001
• Status: Expired due to Term

• Current Assignee: Orise Technology Co., Ltd (FocalTech Systems Co.,Ltd)
• Original Assignee: Sunplus Technology Co., Ltd
• Inventors: Juang, Dar-Chang
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/761,685
• Time in Patent Office: 313 Days
• Field of Search: 323/312-315, 327/535, 327/537, 327/538
• US Class Current: 323/315
• CPC Class Codes: G05F 3/205 Substrate bias-voltage generators for static stores G11C5/146
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• 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 constant current driver with auto-clamped pre-charge function includes a reference bias generator and a plurality of constant current driver cells, each being connected to the reference bias generator to form a respective current mirror. Each constant current driver cell has a switch transistor, a current output transistor and a pre-charge transistor. When a constant current is outputted from the current output transistor for driving an organic light emitting diode, the pre-charge transistor is turned on to provide a drain to source current as an additional large current for rapidly pre-charging the organic light emitting diode until the gate to source voltage of the pre-charge transistor is smaller than the threshold voltage.

Claims

1. A constant current driver with auto-clamped pre-charge function, comprising:

a reference bias generator having a bias output terminal for providing a reference bias; and

a plurality of constant current driver cells, each being connected to the reference bias generator to form a respective current mirror, wherein each constant current driver cell comprises;

a switch transistor controlled by an input terminal for being turned on or off;

a current output transistor connected to the switch transistor and the bias output terminal of the reference bias generator for outputting a constant current when the switch transistor is on; and

a pre-charge transistor having a gate connected to the gate of the current output transistor and further connected to the bias output terminal of the reference bias generator, a drain and a source connected to the drain and source of the current output transistor, respectively, whereby, when a constant current is outputted from the current output transistor for driving an organic light emitting diode, the pre-charge transistor is turned on due to the gate to source voltage thereof being larger than its threshold voltage, so as to provide a drain to source current as an additional large current for rapidly pre-charging the organic light emitting diode until the gate to source voltage of the pre-charge transistor is smaller than the threshold voltage.

2. The constant current driver with auto-clamped pre-charge function, as claimed in claim 1, further comprising a multiplexer connected between the bias output terminal of the reference bias generator and the gates of the pre-charge transistor and the current output transistor of each of the constant current driver cells, the multiplexer having a first and a second input terminals connected to the bias output terminal of the reference bias generator and ground, respectively, and an output terminal connected to the gates of the pre-charge transistor and the current output transistor.

3. The constant current driver with auto-clamped pre-charge function as claimed in claim 1, wherein the constant current driver cell further comprises a discharge transistor connected to the current output transistor for discharging when the discharge transistor is turned on.

4. The constant current driver with auto-clamped pre-charge function as claimed in claim 3, wherein the switch transistor and the current output transistor are PMOS transistors and the discharge transistor and the pre-charge transistor are NMOS transistors.

5. The constant current driver with auto-clamped pre-charge function as claimed in claim 4, wherein the switch transistor has a source connected to a supplied voltage, a drain connected to the source of the current output transistor, and a gate connected to the input terminal;

the gate of the current output transistor is connected to the bias output terminal of the reference bias generator and the drain thereof is used as a constant current output terminal;

the drain of the discharge transistor is connected to the drain of the current output transistor, the source thereof is grounded, and the gate thereof is used as a discharge control terminal.

6. The constant current drive with auto-clamped pre-charge function as claimed in claim 4, wherein the current output transistor has a source connected to a supplied voltage, a drain connected to the source of the switch transistor, and a gate connected to the bias output terminal of the reference bias generator;

the gate of the switch transistor is connected to the input terminal, and the drain thereof is used as the constant current output terminal;

the drain of the discharge transistor is connected to the drain of the switch transistor, the drain thereof is grounded, and the source thereof is used as the discharge control terminal.

7. A constant current driver with auto-clamped pre-charge function comprising:

a reference bias generator having a bias output terminal for providing a reference bias; and

a plurality of constant current driver cells, each being connected to the reference bias generator to form a respective current mirror, wherein each constant current driver cell comprises;

a switch transistor controlled by an input terminal for being turned on and off;

a current output transistor connected to the switch transistor and the bias output terminal of the reference bias generator; and

a diode array having an anode and a cathode connected to the drain and the source of the current output transistor, respectively, wherein when a constant current is outputted from the current output transistor to drive an organic light emitting diode, the diode array is turned on for providing an additional large current to rapidly pre-charge the organic light emitting diode until the voltage of the diode array is smaller than its cut-in voltage.

8. The constant current driver with auto-clamped pre-charge function as claimed in claim 7, wherein the diode array is comprised of one diode or more than one diodes connected in series.

9. The constant current driver with auto-clamped pre-charge function as claimed in claim 8, wherein the diode array includes at least one diode formed by NMOS or PMOS transistor.

10. The constant current driver with auto-clamped pre-charge function as claimed in claim 7, further comprising a multiplexer connected between the bias output terminal of the reference bias generator and the gates of the pre-charge transistor and the current output transistor of each of the constant current driver cells, the multiplexer having a first and a second input terminal connected to the bias output terminal of the reference bias generator and ground, respectively, and an output terminal connected to the gate of the current output transistor.

11. The constant current driver with auto-clamped pre-charge function as claimed in claim 7, wherein the constant current driver cell further comprises a discharge transistor connected to the current output transistor for discharging the current output transistor when the discharge transistor is turned on.

12. The constant current driver with auto-clamped pre-charge function as claimed in claim 11, wherein the switch transistor and the current output transistor are PMOS transistors and the discharge transistor is an NMOS transistor.

13. The constant current driver with auto-clamped pre-charge function as claimed in claim 10, wherein the switch transistor has a source connected to a supplied voltage, a drain connected to the source of the current output transistor, and a gate connected to the input terminal;

the gate of the current output transistor is connected to the bias output terminal of the reference bias generator and the drain thereof is used as a constant current output terminal;

the drain of the discharge transistor is connected to the drain of the current output transistor, the source thereof is grounded, and the gate thereof is used as a discharge control terminal.

14. The constant current driver with auto-clamped pre-charge function as claimed in claim 10, wherein the source of the current output transistor is connected to the supplied voltage, the drain thereof is connected to the source of the switch transistor, and the gate thereof is connected to the bias output terminal of the reference bias generator;

the gate of the switch transistor is connected to the input terminal, and the drain thereof is used as the constant current output terminal;

the drain of the discharge transistor is connected to the drain of the switch transistor, the source thereof is grounded, and the gate thereof is used as the discharge control terminal.