Pixel circuit and driving method thereof

Patent metadata

Field	Value
Publication number	US-10140919-B2
Application number	US-201715857275-A
Country	US
Kind code	B2
Filing date	Dec 28, 2017
Priority date	Jun 27, 2014
Publication date	Nov 27, 2018
Grant date	Nov 27, 2018

Abstract

To prevent image retention, the pixel circuit includes: a light emitting element; a driving transistor which supplies an electric current according to an applied voltage to the light emitting element; a capacitor part which holds the voltage containing a threshold voltage and a data voltage of the driving transistor; and a switch part which has the voltage containing the threshold voltage and the data voltage held to the capacitor part and applies the voltage to the driving transistor. Further, the switch part has a function which applies a constant voltage to the driving transistor before having the voltage containing the threshold voltage and the data voltage held to the capacitor part.

First claim

What is claimed is:

1. A pixel circuit, comprising:
a light emitting element;
a driving transistor which supplies an electric current according to an applied voltage to the light emitting element;
a capacitor part which holds a voltage containing a threshold voltage and a data voltage of the driving transistor; and
a switch part configured to control the voltage containing the threshold voltage and the data voltage to be held in the capacitor part, and to apply the voltage containing the threshold voltage and the data voltage to the driving transistor,
wherein
the switch part applies a constant voltage to the driving transistor before making the capacitor part hold the voltage containing the threshold voltage and the data voltage, and further comprises a current detour transistor which makes the electric current supplied from the driving transistor detour without flowing through the light emitting element, wherein:
the driving transistor comprises a gate terminal, a source terminal, and a drain terminal, and supplies an electric current according to a voltage applied between the gate terminal and the source terminal to the light emitting element that is connected in series to the drain terminal and the source terminal; and
the switch part:
comprises, in addition to the current detour transistor, a data voltage transistor which inputs the data voltage from a data supply line, a short-circuit transistor which functions as a switch for short-circuiting the gate terminal and the drain terminal, a gate voltage transistor which applies the voltage held to the capacitor part between the gate terminal and the source terminal, and a power switching transistor which functions as a switch of an electric current flown to the drain terminal and the source terminal from a power supply voltage line,
applies the constant voltage between the gate terminal and the source terminal by turning on the current detour transistor, the data voltage transistor, the short-circuit transistor, the gate voltage transistor, and the power switching transistor, and makes the current supplied from the driving transistor detour without flowing through the light emitting element via the current detour transistor which is turned on,
makes the capacitor part hold the voltage containing the threshold voltage and the data voltage by turning on the current detour transistor, the data voltage transistor, and the short-circuit transistor and turning off the gate voltage transistor and the power switching transistor, and
applies the voltage held to the capacitor part between the gate terminal and the source terminal by turning off the current detour transistor, the data voltage transistor, and the short-circuit transistor and turning on the gate voltage transistor and the power switching transistor.

2. The pixel as claimed in claim 1 , wherein
ON/OFF of the current detour transistor and the short-circuit transistor are controlled by the same gate signal.

3. The pixel circuit as claimed in claim 1 , wherein
the capacitor part connects the power supply line and the gate terminal of the driving transistor;
the gate voltage transistor connects the power supply line and the source terminal of the driving transistor;
the data voltage transistor connects the data supply line and the source terminal of the driving transistor;
the short-circuit transistor connects the gate terminal of the driving transistor and the drain terminal of the driving transistor;
the power switching transistor connects the drain terminal of the driving transistor and a first terminal of the light emitting element;
the current detour transistor connects the first terminal of the light emitting element and a fourth power supply line; and
a second terminal of the light emitting element is connected to a second power supply line.

4. The pixel circuit as claimed in claim 1 , wherein
the capacitor part connects the gate terminal of the driving transistor and a first terminal of the light emitting element;
the gate voltage transistor connects the power supply line and the drain terminal of the driving transistor;
the data voltage transistor connects the data supply line and the source terminal of the driving transistor;
the short-circuit transistor connects the gate terminal of the driving transistor and the drain terminal of the driving transistor;
the power switching transistor connects the source terminal of the driving transistor and a first terminal of the light emitting element;
the current detour transistor connects the first terminal of the light emitting element and a fourth power supply line; and
a second terminal of the light emitting element is connected to a second power supply line.

5. A pixel circuit, comprising:
a light emitting element;
a driving transistor which supplies an electric current to the light emitting element according to a voltage applied to a gate terminal of the driving transistor;
a capacitor part which holds an emitting voltage containing a threshold voltage of the driving transistor and a data voltage; and
a switch part which holds the emitting voltage in the capacitor part, and applies the emitting voltage which is held by the capacitor part to the gate terminal of the driving transistor, wherein
the switch part applies a prescribed voltage to the gate terminal of the driving transistor, and the driving transistor supplies an electric current corresponding to the prescribed voltage which is applied by the switch part, before making the capacitor part hold the emitting voltage,
the switch part further comprises a current detour transistor which makes the electric current supplied from the driving transistor detour without flowing through the light entitling element before making the capacitor part hold the emitting voltage, and
the electric current supplied from the driving transistor corresponds to the prescribed voltage,
the driving transistor comprises the gate terminal, a source terminal, and a drain terminal, and supplies an electric current according to a voltage applied between the gate terminal and the source terminal to the light emitting element that is connected in series to the drain terminal and the source terminal,
the switch part comprises:
a data voltage transistor which inputs the data voltage from a data supply line, a reference voltage transistor which inputs a reference voltage from a reference voltage line,
a gate voltage transistor which applies the voltage held to the capacitor part between the gate terminal and the source terminal, and
a power switching transistor which function as a switch of an electric current flown to the drain terminal and the source terminal from a power supply voltage line,

the switch part applies the constant voltage between the gate terminal and the source terminal by turning on the data voltage transistor, the reference voltage transistor, the gate voltage transistor, and the power switching transistor,
the switch part makes the capacitor part hold the voltage containing the threshold voltage and the data voltage by turning on the data voltage transistor and the reference voltage transistor and turning off the gate voltage transistor and the power switching transistor, and
the switch part applies the voltage held to the capacitor part between the gate terminal and the source terminal by turning off the data voltage transistor and the reference voltage transistor and turning on the gate voltage transistor and the power switching transistor, wherein
a second terminal of the capacitor part is connected to the source terminal of the driving transistor;
the reference voltage transistor connects the reference voltage line and a first terminal of the capacitor part;
the data voltage transistor connects the data supply line and the gate terminal of the driving transi

Assignees

• Tianma Japan Ltd

Inventors

• Nonaka Yoshihiro
• Matsueda Yojiro
• Takatori Kenichi

Classifications

• G09G2300/0842

  forming a memory circuit, e.g. a dynamic memory with one capacitor · CPC title

• G09G2300/08

  Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements · CPC title

• G09G2320/0257

  Reduction of after-image effects · CPC title

• G09G3/325 Primary

  the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver · CPC title

• G09G2320/045

  Compensation of drifts in the characteristics of light emitting or modulating elements · CPC title