PIXEL CIRCUIT, DISPLAY APPARATUS, AND PIXEL CIRCUIT DRIVE CONTROL METHOD

• US 20090244046A1
• Filed: 03/26/2009
• Published: 10/01/2009
• Est. Priority Date: 03/26/2008
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Seto, Yasuhiro
• Granted Patent: US 8,368,678 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3225 using an active matrix
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes

Abstract

A pixel circuit including a light emitting element, a driving transistor, connected to the light emitting element, that applies a drive current to the light emitting element, a holding circuit connected to a gate terminal of the driving transistor, and a switching transistor connected between the holding circuit and a data line through which a data signal to be held by the holding circuit flows, in which the driving transistor and the switching transistor are inorganic oxide thin film transistors whose OFF-operation threshold voltage is a negative voltage, and the holding circuit includes a first capacitor element connected between the switching transistor and the gate terminal of the driving transistor, and a second capacitor element connected between a point located between the first capacitor element and the gate terminal of the driving transistor and a voltage source that supplies a negative voltage.

Claims

1. A pixel circuit comprising:

a light emitting element,

a driving transistor, connected to the light emitting element, that applies a drive current to the light emitting element,

a holding circuit connected to a gate terminal of the driving transistor, and

a switching transistor connected between the holding circuit and a data line through which a data signal to be held by the holding circuit flows, wherein;

the driving transistor and the switching transistor are inorganic oxide thin film transistors whose OFF-operation threshold voltage is a negative voltage; and

the holding circuit includes a first capacitor element connected between the switching transistor and the gate terminal of the driving transistor, and a second capacitor element connected between a point located between the first capacitor element and the gate terminal of the driving transistor and a voltage source that supplies a negative voltage.

2. A display apparatus, comprising

an active matrix substrate on which the pixel circuit as claimed in claim 1 is disposed in a large number;

a scan drive circuit that supplies to each switching transistor a scanning signal for turning ON/OFF each switching transistor; and

a data drive circuit that supplies the data signal to be held by the holding circuit,

wherein the scan drive circuit is a circuit that supplies a positive voltage as the scanning signal and the data drive circuit is a circuit that supplies a positive voltage as the data signal.

3. The display device as claimed in claim 2, the negative voltage VB supplied to the second capacitor element, a capacitance C1 of the first capacitor element, a capacitance C2 of the second capacitor element, and the threshold voltage VTH satisfy the relationship of Formula (1) below, and a minimum setting value V_datamin of the data signal, an OFF scan signal V_scan(off), and the threshold voltage VTH satisfy the relationship of Formula (2) below.

VB≦

(1+2×

C2/C1)×

VTH  

 

(1)

V_datamin≧

V_scan(off)−

VTH  

 

(2)

4. A pixel circuit comprising:

a light emitting element; and

an inorganic oxide thin film transistor whose OFF-operation threshold voltage is a negative voltage,

wherein a negative voltage is used as the gate-source voltage of the inorganic oxide thin film transistor to control the drive current of the light emitting element.

5. A pixel circuit drive control method for drive controlling a pixel circuit having a light emitting element and an inorganic oxide thin film transistor whose OFF-operation threshold voltage is a negative voltage,

wherein a negative voltage is used as the gate-source voltage of the inorganic oxide thin film transistor to control the drive current of the light emitting element.