Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2001-09-28
2004-11-23
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S099000, C345S204000
Reexamination Certificate
active
06822645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device and in particular to a driving device for a display device adapted for a power save request.
2. Description of the Related Art
Flat panel display devices such as liquid crystal and organic EL display devices are generally thin, lightweight, and energy efficient. Because of these characteristics, flat panel display devices are suited for use as display devices for portable devices, such as mobile phones, and have therefore come to be widely employed in many such portable devices.
A liquid crystal display device comprises a liquid crystal display (LCD) panel constructed by sealing liquid crystal between a pair of substrates, a driving circuit for driving the LCD panel, and a power supply circuit for supplying the required supply voltages to the driving circuit and LCD panel. Because the LCD is not self-illuminating, a light source is provided at the rear side of the panel in LCDs other than a reflective type LCD, such as transmission type LCD and transflective type LCD.
There is a strong demand for reducing the power consumption in portable instruments such as mobile phones. In order to satisfy this demand, there are techniques employed such as, for example, switching off the light source during waiting periods because the light source consumes the most power.
Where there is a further demand for reducing the power consumption in a display device, the power supply circuit may be controlled to turn off the power supply for the device.
However, when the power supply is turned off during the power save mode, the display device will be unable to display. In a mobile phone, for example, when the power save mode is activated, because the display power supply is controlled to be turned off, information such as the time of day indicated by the internal clock and radio wave conditions cannot be shown, even when desired. If one wishes to see the display, there is a need to manually turn on the display, which is inconvenient.
SUMMARY OF THE INVENTION
The present invention was conceived to solve at least the problem described above, and one object of the present invention is to provide a display device which is adapted for a power save mode, and, at the same time, allows the display to be seen even in the power save mode.
In order to achieve at least the object mentioned above, the present invention is characterized in the following.
According to one aspect of the present invention, there is provided a driving device for a display device, comprising a driving circuit for driving a display panel onto which a plurality of pixels are formed; and a power supply circuit for generating supply voltage for the display panel and the driving circuit; wherein when power save is instructed, the supply voltage supplied to one or both of the display panel and the driving circuit is controlled to be turned on and off with a predetermined period.
According to another aspect of the present invention, it is preferable in the driving device that the driving device further comprises timer and the power supply circuit turns the supply voltage on and off in response to the time measurement result by the timer.
In this manner, the output of supply voltage is controlled to be periodically turned on and off when power save is instructed. When the supply voltage is controlled to be turned off, because the power consumption at the driving circuit or display panel can be shut off, the power consumption of the display device can be reduced. Because the supply voltage is controlled to be periodically turned on during the power save mode, even during the power save mode the user can periodically view the display without any manipulation.
According to another aspect of the present invention, it is preferable in the driving device that the display panel comprises a plurality of pixels, selection lines for selecting the pixels, and data lines for supplying data to the pixels; the driving device further comprises suspension controller for suspending, when a power save is instructed, the output of all selection signals onto the selection lines for selecting the pixels to which data is written; and the supply voltage is controlled to be turned off after the suspension controller has suspended the output of the selection signals.
By controlling the supply voltage to be turned off after suspending the output of the selection signals, for example, in an active matrix type panel wherein a switching element such as a transistor is formed on each pixel, the switching element can be reliably controlled to be turned off before the supply voltage is reduced. The inclusion of the capacitor component enables the data written to the pixel during when the switching element is at “on” state to be retained in each pixel for a predetermined period even after the switching element is turned off. Thus, by first suspending the output of all selection signals to the selection lines and then turning off the supply voltage, the display according to the data maintained till immediately before the turn off operation can be shown at each pixel even when the power supply is turned off, similar to the non-selection period during the normal operation.
With the present invention, it is possible to execute the control to turn off the supply voltage after, for example, 1 vertical scan period has elapsed since the suspension of the output of the selection signals by the suspension controller. In a driving device, the vertical synchronization signal generated every vertical scan period is used for many purposes, and, thus, by controlling the off timing with reference to the vertical scan period, no designated control signal for suspension is needed. Therefore, there is no need for a major circuit alteration to allow for such.
As described above, in the driving device for a display device according to the present invention, the supply voltage can be controlled to be periodically turned on and off with a predetermined period when power save is instructed. Because of this control to turn off the supply voltage, the power consumption at the driving circuit and display panel can be shut off, and, thus, the power consumption in the display device can be reduced. At the same time, because the supply voltage is controlled to turn on automatically at a regular interval in the power save mode, the display can be viewed periodically.
Moreover, according to the present invention, the supply voltage is controlled to be turned off after the output of the selection signals are suspended. Due to the capacitor component of the pixels, each pixel can maintain the display, which has been shown until immediately before the power supply is turned off, for a predetermined amount of time even during the period when the power supply is turned off and no power is consumed.
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Noritake Kazuto
Tsutsui Yusuke
Hogan & Hartson LLP
Said Mansour M.
Sanyo Electric Co,. Ltd.
Shalwala Bipin
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