Display apparatus having a threshold voltage and mobility correcting period and method for driving the same
View Patent ↗In a display apparatus, as shown in FIG. 1, by using a reference signal, a shift register and a logical operation circuit generate a driving signal in periods for correcting a threshold voltage based on a rectangular wave signal. Also by using the reference signal, a write signal in a mobility correcting period is generated by an inverter, a NAND circuit, a level conversion circuit, a buffer circuit, a driving power generating unit, and a low-pass filter including a resistor and a capacitor. The signals are separately generated and are selectively output. Thus, excessive or insufficient mobility correction based on emission brightness can be prevented.
1. A display apparatus comprising:
a pixel section having pixels arranged in a matrix; and
a horizontal driving circuit and a vertical driving circuit configured to drive signal lines and scanning lines in the pixel section, whereby an image is displayed in the pixel section,
wherein each pixel includes
a light-emitting element,
a signal-level-holding capacitor,
a write transistor configured to be turned on and off by a write signal output from the vertical driving circuit, and configured to set a terminal voltage of the signal-level-holding capacitor to a signal level of one signal line, and
a driving transistor having a gate and a source to which ends of the signal-level-holding capacitor are connected, the driving transistor being configured to cause the light-emitting element to emit light by driving the light-emitting element in accordance with a voltage across the gate and source of the driving transistor,
wherein, in a threshold voltage correcting period in a non-emission period in which light emission by the light-emitting element is stopped, after the write signal turns on the write transistor to set potentials at ends of the signal-level-holding capacitor to predetermined potentials, a threshold voltage of the driving transistor is set in the signal-level-holding capacitor by discharging stored charge of the signal-level-holding capacitor through the driving transistor,
wherein, in a mobility correcting period in the non-emission period in which the light emission by the light-emitting element is stopped, the mobility correcting period following the threshold voltage correcting period, after the write signal turns on the write transistor to set a voltage at one end of the signal-level-holding capacitor to the signal level of the one signal line, the driving transistor charges the other end of the signal-level-holding capacitor by turning on the driving transistor,
wherein a fall of the write signal turns off the write transistor, and
wherein the vertical driving circuit includes
a threshold-voltage-correcting-period write-signal generating unit configured to generate the write signal in the threshold voltage correcting period,
a mobility-correcting-period write-signal generating unit configured to generate the write signal in the mobility correcting period, and
a selective output unit configured to selectively output, to the pixel, the write signal in the threshold voltage correcting period and the write signal in the mobility correcting period.
2. The display apparatus according to claim 1 ,
wherein the threshold-voltage-correcting-period write-signal generating unit generates the write signal in the threshold voltage correcting period by using a rectangular wave signal, and
wherein the mobility-correcting-period write-signal generating unit generates the write signal in the mobility correcting period by smoothing a rising edge and/or falling edge of a signal level.
3. The display apparatus according to claim 2 ,
wherein the mobility-correcting-period write-signal generating unit includes
a selection-signal generating unit configured to generate a selection signal corresponding to the write signal in the mobility correcting period,
a buffer circuit configured to receive the selection signal and to output an output signal, and
a power-supply-voltage control circuit configured to change a power-supply voltage of the buffer circuit on the basis of a signal waveform corresponding to the write signal in the mobility correcting period,
wherein the write signal in the mobility correcting period is generated by the buffer circuit on the basis of a change in the power-supply voltage by using the power-supply-voltage control circuit.
4. A driving method for a display apparatus which includes a pixel section having pixels arranged in a matrix, and a horizontal driving circuit and a vertical driving circuit configured to drive signal lines and scanning lines in the pixel section, whereby an image is displayed in the pixel section,
in which each pixel includes
a light-emitting element,
a signal-level-holding capacitor,
a write transistor configured to be turned on and off by a write signal output from the vertical driving circuit, and configured to set a terminal voltage of the signal-level-holding capacitor to a signal level of one signal line, and
a driving transistor having a gate and a source to which ends of the signal-level-holding capacitor are connected, the driving transistor being configured to cause the light-emitting element to emit light by driving the light-emitting element in accordance with a voltage across the gate and source of the driving transistor,
in which, in a threshold voltage correcting period in a non-emission period in which light emission by the light-emitting element is stopped, after the write signal turns on the write transistor to set potentials at ends of the signal-level-holding capacitor to predetermined potentials, a threshold voltage of the driving transistor is set in the signal-level-holding capacitor by discharging stored charge of the signal-level-holding capacitor through the driving transistor,
in which, in a mobility correcting period in the non-emission period in which the light emission by the light-emitting element is stopped, the mobility correcting period following the threshold voltage correcting period, after the write signal turns on the write transistor to set a voltage at one end of the signal-level-holding capacitor to the signal level of the one signal line, the driving transistor charges the other end of the signal-level-holding capacitor by turning on the driving transistor, and
in which a fall of the write signal turns off the write transistor,
the driving method comprising the steps of:
generating the write signal in the threshold voltage correcting period and the write signal in the mobility correcting period; and
selectively outputting, to the pixel, the write signal in the threshold voltage correcting period and the write signal in the mobility correcting period.