Display apparatus, driving method thereof and electronic instrument

• US 20090179838A1
• Filed: 12/08/2008
• Published: 07/16/2009
• Est. Priority Date: 01/15/2008
• Status: Active Grant

• Current Assignee: JDI Design and Development GK
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Uchino, Katsuhide, Yamashita, Junichi
• Granted Patent: US 9,153,169 B2
• Time in Patent Office: Days
• US Class Current: 345/84
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

An image display apparatus includes a pixel array section and a drive section configured to drive the pixel array section. The pixel array section is a pixel-circuit matrix with pixel circuits each serving as a matrix element. The drive section has at least a write scanner for supplying the control signal to each of the scan lines in order to carry out a sequential scanning operation on the scan lines for every field and a signal selector for supplying a video signal to each of the signal lines with a timing adjusted to the sequential scanning operation. Each of the pixel circuits employs at least a sampling transistor, a drive transistor, a signal holding capacitor and a light emitting device.

Claims

1. An image display apparatus comprising

a pixel array section and a drive section configured to drive said pixel array section, wherein:

said pixel array section is a pixel-circuit matrix with pixel circuits each serving as a matrix element;

each of said pixel circuits is provided at an intersection of a scan line stretched as one of rows of said matrix to serve as a line for supplying a control signal to said pixel circuit and a signal line stretched as one of columns of said matrix to serve as a line for supplying a video signal to said pixel circuit and is connected to said scan line and said signal line;

said drive section has at least a write scanner for supplying said control signal to each of said scan lines in order to carry out a sequential scanning operation on said scan lines for every field and a signal selector for supplying a video signal to each of said signal lines with a timing adjusted to said sequential scanning operation;

each of said pixel circuits employs at least a sampling transistor, a drive transistor, a signal holding capacitor and a light emitting device;

the gate electrode of said sampling transistor is connected to one of said scan lines;

the source and drain electrodes of said sampling transistor are connected between one of said signal lines and the gate electrode of said drive transistor;

the drain electrode of said drive transistor is connected to a power-supply line whereas the source electrode of said drive transistor is connected to said light emitting device;

said signal holding capacitor is connected between said gate and source electrodes of said drive transistor;

said sampling transistor enters a turned-on state in accordance with a control signal supplied by said scan line, sampling a video signal supplied by said signal line and then stores said sampled video signal into said signal holding capacitor;

said drive transistor supplies said light emitting device with a driving current having a magnitude according to said video signal held by said signal holding capacitor;

each of said pixel circuits operates in a light emission period and a no-light emission period which together compose the period of a field;

said signal selector provides each of said signal lines with a video signal, and a predetermined reference potential for driving said light emitting device to cease to emit light;

said write scanner provides each individual one of said scan lines with said control signal for acquiring said video signal from said individual signal line, and another control signal for acquiring said predetermined reference potential from said individual signal line;

said sampling transistor acquires said predetermined reference potential from said signal line in accordance with said other control signal supplied by said write scanner, applying said predetermined reference potential to said gate electrode of said drive transistor in order to drive said light emitting device to cease to emit light and make a transition from said no-light emission period to said light emission period; and

by applying said predetermined reference potential to said gate electrode of said drive transistor, a voltage applied between said gate and source electrodes of said drive transistor is put in a state of a reverse bias, the magnitude of which is determined by the level of said video signal, so as to repress variations of the threshold voltage of said drive transistor.

2. The image display apparatus according to claim 1,

wherein said signal selector sets said predetermined reference potential at an optimal value so that:

when said video signal is set at a white level, said voltage applied between said gate and source electrodes of said drive transistor is put in a state of a maximum reverse bias; and

when said video signal is set at a black level, said voltage applied between said gate and source electrodes of said drive transistor becomes a zero level or approaches said zero level, entering a state of a minimum reverse bias.

3. The image display apparatus according to claim 1,

wherein said write-scanner provides said scan line with a control pulse serving as said other control signal so that, with a fixed trip supplied to said source electrode of said drive transistor, said sampling transistor instantaneously applies said predetermined reference potential to said gate electrode of said drive transistor to reverse an electric potential at said gate electrode of said drive transistor with respect to said fixed electric potential at said source electrode of said drive transistor, putting said drive transistor in a state of a reverse bias.

4. The image display apparatus according to claim 1,

wherein said write scanner adjusts the phase of said other control signal supplied to said scan line in order to optimize a ratio of said light emission period to said no-light emission period so that a threshold-voltage change in a state of a forward bias applied between said gate and source electrodes of said drive transistor during said light emission period is canceled by a threshold-voltage change in a state of a reverse bias applied between said gate and source electrodes of said drive transistor during said no-light emission period.

5. The image display apparatus according to claim 1,

wherein, prior to an operation to sample said video signal, said driving current is flowed through said drive transistor till said drive transistor is put in a turned-off state of cutting off said current flowing through drive transistor and a voltage, which is appearing between said gate and source electrodes of said drive transistor at the time said driving current flowing through said drive transistor is cut off, is stored in said signal holding capacitor in order to carry out a threshold-voltage compensation operation to compensate said drive transistor for an effect of variations in threshold voltage from pixel to pixel.

6. The image display apparatus according to claim 1,

wherein, when said sampling transistor is put in a turned-on state in order to store said video signal in said signal holding capacitor, said driving current flowing through said drive transistor is negatively fed back to said signal holding capacitor during a mobility compensation period determined in advance in order to compensate said drive transistor for an effect of variations in carrier mobility.

7. An electronic instrument employing an image display apparatus including

a pixel array section and a drive section configured to drive said pixel array section, wherein:

said pixel array section is a pixel-circuit matrix with pixel circuits each serving as a matrix element;

each of said pixel circuits is provided at an intersection of a scan line stretched as one of rows of said matrix to serve as a line for supplying a control signal to said pixel circuit and a signal line stretched as one of columns of said matrix to serve as a line for supplying a video signal to said pixel circuit and is connected to said scan line and said signal line;

said drive section has at least a write scanner for supplying said control signal to each of said scan lines in order to carry out a sequential scanning operation on said scan lines for every field and a signal selector for supplying a video signal to each of said signal lines with a timing adjusted to said sequential scanning operation;

each of said pixel circuits employs at least a sampling transistor, a drive transistor, a signal holding capacitor and a light emitting device;

the gate electrode of said sampling transistor is connected to one of said scan lines;

the source and drain electrodes of said sampling transistor are connected between one of said signal lines and the gate electrode of said drive transistor;

the drain electrode of said drive transistor is connected to a power-supply line whereas the source electrode of said drive transistor is connected to said light emitting device;

said signal holding capacitor is connected between said gate and source electrodes of said drive transistor;

said sampling transistor enters a turned-on state in accordance with a control signal supplied by said scan line, sampling a video signal supplied by said signal line and then stores said sampled video signal into said signal holding capacitor;

said drive transistor supplies said light emitting device with a driving current having a magnitude according to said video signal held by said signal holding capacitor;

each of said pixel circuits operates in a light emission period and a no-light emission period which together compose the period of a field;

said signal selector provides each of said signal lines with a video signal, and a predetermined reference potential for driving said light emitting device to cease to emit light;

said write scanner provides each individual one of said scan lines with said control signal for acquiring said video signal from said individual signal line, and another control signal for acquiring said predetermined reference potential from said individual signal line;

said sampling transistor acquires said predetermined reference potential from said signal line in accordance with said other control signal supplied by said write scanner, applying said predetermined reference potential to said gate electrode of said drive transistor in order to drive said light emitting device to cease to emit light and make a transition from said no-light emission period to said light emission period; and

by applying said predetermined reference potential to said gate electrode of said drive transistor, a voltage applied between said gate and source electrodes of said drive transistor is put in a state of a reverse bias, the magnitude of which is determined by the level of said video signal, so as to repress variations of the threshold voltage of said drive transistor.

8. A driving method for driving an image display apparatus including a pixel array section and a drive section configured to drive said pixel array section in which

said pixel array section is a pixel-circuit matrix with pixel circuits each serving as a matrix element,

each of said pixel circuits is provided at an intersection of a scan line stretched as one of rows of said matrix to serve as a line for supplying a control signal to said pixel circuit and a signal line stretched as one of columns of said matrix to serve as a line for supplying a video signal to said pixel circuit and is connected to said scan line and said signal line,

said drive section has at least a write scanner for supplying said control signal to each of said scan lines in order to carry out a sequential scanning operation on said scan lines for every field and a signal selector for supplying a video signal to each of said signal lines with a timing adjusted to said sequential scanning operation,

each of said pixel circuits employs at least a sampling transistor, a signal holding capacitor, a drive transistor and a light emitting device,

the gate electrode of said sampling transistor is connected to one of said scan lines,

the source and drain electrodes of said sampling transistor are connected between one of said signal lines and the gate electrode of said drive transistor,

the drain electrode of said drive transistor is connected to a power-supply line whereas the source electrode of said drive transistor is connected to said light emitting device,

said signal holding capacitor is connected between said gate and source electrodes of said drive transistor,

said sampling transistor enters a turned-on state in accordance with a control signal supplied by said scan line, sampling a video signal supplied by said signal line and then stores said sampled video signal into said signal holding capacitor, and

said drive transistor supplies said light emitting device with a driving current having a magnitude according to said video signal held by said signal holding capacitor, wherein:

each of said pixel circuits operates in a light emission period and a no-light emission period which together compose the period of a field;

said signal selector provides each of said signal lines with a video signal, and a predetermined reference potential for driving said light emitting device to cease to emit light;

said write scanner provides each individual one of said scan lines with said control signal for acquiring said video signal from said individual signal line, and another control signal for acquiring said predetermined reference potential from said individual signal line;

said sampling transistor acquires said predetermined reference potential from said signal line in accordance with said other control signal supplied by said write scanner, applying said predetermined reference potential to said gate electrode of said drive transistor in order to drive said light emitting device to cease to emit light and make a transition from said no-light emission period to said light emission period; and

in addition, by applying said predetermined reference potential to said gate electrode of said drive transistor, a voltage applied between said gate and source electrodes of said drive transistor is put in a state of a reverse bias, the magnitude of which is determined by the level of said video signal, so as to repress variations of the threshold voltage of said drive transistor.