WO2010089682A1

WO2010089682A1 - Display system and method of operation therefor

Info

Publication number: WO2010089682A1
Application number: PCT/IB2010/050377
Authority: WO
Inventors: Charayaphan Charoensak
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-02-03
Filing date: 2010-01-28
Publication date: 2010-08-12

Abstract

A display system comprises a display panel unit (103) and a control unit (101) coupled thereto using an interface (105) providing a main video data channel and an auxiliary data channel. A video signal is generated from an input video signal and transmitted to the display panel unit (103) using the main video data channel. Furthermore, the control unit (101) determines a backlight dimming setting in response to the input video signal and transmits it to the display panel unit (103) in the auxiliary control data channel. The interface video signal may comprise pixel values that are compensated for the backlight setting. The display panel unit (103) varies the backlight dependent on the backlight indication thereby providing a display system with efficient dynamic backlight dimming. The invention may allow a standardized interface to be used when distributing display functionality between different units and may allow lower complexity display panel units with reduced form factor to be manufactured.

Description

Display system and method of operation therefor

FIELD OF THE INVENTION

The invention relates to a display system comprising a display panel and in particular, but not exclusively, to a display system comprising a Liquid Crystal Display (LCD) panel.

BACKGROUND OF THE INVENTION

Display systems using display panels such as Liquid Crystal Display (LCD) panels have become ubiquitous and are used for many applications. For example, flat screen televisions using LCD display panels have become very popular. It is desirable to have a display unit with as small a form factor as is possible for a given display size, and in particular it is generally desirable for display units to be as thin as possible. In order to reduce the volume and in particular the depth of display units, it has been proposed to move some functionality to an external control box. For example, televisions have been developed wherein the functionality in the display unit is minimized as much as possible by concentrating the majority of the control functionality in an external control unit. This control unit may specifically comprise input connectors, switching circuitry for switching between different inputs, video processing for processing input video signals to generate suitable signals for the display panel, video decoding functionality etc. An additional benefit of concentrating such functionality in an external control box is that the power requirements for the display unit can be reduced thereby reducing the constraints on the form factor and thermal design.

However, for such a distributed system, the exact distribution of functionality is critical for optimized functionality. Furthermore, the need for communicating signals between the control unit and the display unit requires a highly efficient interface to be implemented between the control unit and the display unit. Typically, such an interface is implemented using a proprietary connection comprising separate and individual connections for the required control operations.

However, typical known approaches tend to be suboptimal and hence an improved display system would be advantageous. In particular, a display system allowing increased flexibility, reduced cost, improved image quality, reduced resource requirements, a reduced form factor of the display module, reduced power consumption, increased interoperability or compatibility with other display systems and/or standards and/or improved performance would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to an aspect of the invention there is provided a display system comprising: a display panel unit having an external input video connector; and a control unit having an external output video connector, the display unit (103) and control unit (101) being arranged to be coupled together by an interface connected to the external output video connector and to the external input video connector, the interface providing a main video data channel and an auxiliary data channel; wherein the control unit comprises: means for generating a first video signal for the display panel unit from an input video signal, means for transmitting the first video signal to the display panel unit using the main video data channel, means for determining a backlight dimming setting for the display panel unit in response to the input video signal, and means for transmitting a backlight indication indicative of the backlight dimming setting to the display panel unit in the auxiliary data channel; and the display panel unit comprises: a display panel, means for receiving the first video signal in the main video data channel, a display driver for generating a display panel drive signal in response to the first video signal and feeding it to the display panel, means for receiving the backlight indication in the auxiliary data channel, and a backlight controller for controlling a backlight characteristic for the display panel in response to the backlight indication. The inventor of the current invention has realized that a particular problem of distributing functionality between a display panel unit and a control unit is that of how to address backlight issues. In particular, the inventor has realized that advantageous and efficient backlight control requires evaluation of the video signal which may be complex and resource demanding and therefore may preferably be located in the control unit. However, as the actual backlight manipulation must be realized in the display panel unit, the inventor has realized that rather than merely providing backlight control connections in a connecting cable between the control unit and the display panel unit, advantageous performance can be achieved by using a more flexible approach. In particular, an advantageous approach may use an interface that provides both a main video data channel and an auxiliary (control) data channel. Specifically, the video signal may be communicated in the main video data channel and the auxiliary data channel may used to supplement this video data by providing dynamic backlight control data which can be processed directly by the functionality in the display panel unit. The approach may allow an improved display system. In particular, a reduced form factor and/or power requirement and/or computational resource requirement for the display panel unit can often be achieved. Furthermore, efficient backlight control may be achieved thereby e.g. allowing reduced power consumption and/or improved image quality. The approach may specifically allow a flexible and even a standardized interface to be used between the control unit and the display panel unit thereby allowing increased flexibility, interoperability and typically lower cost for the end user.

The display panel may specifically be a Liquid Crystal Display (LCD) panel. The auxiliary data channel may communicate control data (bits) from the control unit to the display panel unit and possibly also from the display panel unit to the control unit (i.e. it may be bidirectional). A new backlight parameter may be calculated for each frame of the first video signal and e.g. a new backlight indication may be transmitted for each frame of the first video signal.

The interface may specifically be a cable comprising a connector at each end for connecting to respectively the external output video connector and the external input video connector. The approach may allow an external video interface cable to be used that is longer than e.g. 50 cm or even 1 meter. The external output video connector may in addition to being capable of outputting video data also be capable of receiving data, such as e.g. control data or video data. Also, the external input video connector may in addition to being capable of receiving video data also be capable of outputting data, such as e.g. control data or video data.

In accordance with an optional feature of the invention, the backlight setting is a backlight duty cycle setting.

This may allow a particular advantageous operation in many embodiments. Specifically, the duty cycle may be determined to correspond to a corresponding average intensity of the backlight. The required functionality of the panel display module required to implement a duty cycle backlight control may be kept low and the approach may furthermore allow a low data rate communication of backlight information on the auxiliary control data channel. The feature may specifically provide Pulse Width Modulation (PWM) backlight control data.

In accordance with an optional feature of the invention, the backlight controller is arranged to synchronize a duty cycle of the backlight to a vertical synchronization of the display panel drive signal.

This may allow improved performance and may in particular provide improved image quality. Specifically, the perceived screen flicker may typically be reduced. The backlight controller may specifically align a switching on or off of the backlight to the vertical synchronization. The duty cycle backlight operation may be aligned to the display panel refresh timing. The synchronization may include setting a frequency of the backlight duty cycle operation as a multiple of the refresh rate of the display panel. The pulse width for the backlight duty cycle operation may be set to provide the duty cycle indicated by the backlight indication.

In accordance with an optional feature of the invention, the main video data channel and the auxiliary data channel are not synchronized and the backlight controller is arranged to synchronize a duty cycle of the backlight to a vertical synchronization of the first video signal.

This may allow improved performance and may in particular provide improved image quality. Specifically, the perceived screen flicker may typically be reduced. The backlight controller may align a switching on or off to explicit or implicit vertical synchronization data of the first video signal. The duty cycle backlight operation may be aligned to display panel refresh timing directly or indirectly represented by data in the first video signal.

The system may allow efficient dynamic backlight control using a non- synchronous control data communication together with a synchronous main video data channel. Specifically, the inventor has realized that synchronous backlight information can be communicated over an interface comprising only a no n- synchronous auxiliary (control) data channel. Furthermore, the approach may be implemented while still maintaining very low complexity of the display panel unit as only low complexity functionality is necessary to provide the required synchronization between data of the different channels of the interface.

In accordance with an optional feature of the invention, the interface is a DisplayPort interface.

The inventor has realized that a DisplayPort interface can be used between separate display panel units and control units while at the same time providing an efficient backlight control. The approach may allow the use of a standardized display interface to connect separate display panel units and control units while still providing customized and e.g. proprietary control over the dynamic backlight setting.

In accordance with an optional feature of the invention, the display driver comprises a conversion processor for converting the first video signal from a first video signal format to a second video signal format of the display panel drive signal.

This may allow improved and/or facilitated operation in many embodiments. In particular it may allow an efficient interface communication to be combined with specific requirements for the display panel. The first video signal format may for example be a format standardized for the interface and the second video signal format may be a format standardized/specified for the display panel (e.g. by the display panel manufacturer).

In accordance with an optional feature of the invention, the first video format is a DisplayPort video signal format and the second video signal format is a Low- Voltage Differential Signalling video signal format. The may provide particularly advantageous display performance (and specifically dynamic backlight control) while supporting the use of standardized elements. This may specifically allow reduced cost and/or flexibility for the user.

In accordance with an optional feature of the invention, the display driver and the backlight controller are implemented in a single integrated circuit. This may provide a particularly advantageous embodiment and may especially allow a reduced form factor and/or resource consumption of the display panel unit. The approach may typically provide reduced cost.

In accordance with an optional feature of the invention, the display panel unit further comprises: means for receiving capability data via the auxiliary data channel, the capability data being indicative of capabilities of a unit providing the capability data; means for switching between a first backlight mode and a second backlight mode of operation in response to a determination of whether the capability data comprises an indication of support for dynamic backlight operation, wherein the backlight controller is arranged to change the backlight parameter in response to the backlight indication when operating in the first mode of operation but not when operating in the second mode of operation.

This may allow improved compatibility and interoperability of the display system. Specifically, when a suitably equipped display panel unit is coupled to a suitably equipped control unit using e.g. a standardized interface (e.g. such as DisplayPort), a highly efficient and customized backlight control may be employed. However, at the same time the display panel unit may work with a control unit that does not have such functionality and may simply be coupled to this control unit using the standardized interface (e.g. such as a DisplayPort cable).

When operating in the second backlight mode, the backlight of the display panel may be set to a constant value (e.g. may constantly be set to be on with a constant intensity).

In accordance with an optional feature of the invention, the control unit further comprises: means for receiving capability data via the auxiliary data channel, the capability data being indicative of capabilities of a unit providing the capability data; means for switching between a first backlight mode and a second backlight mode of operation in response to a determination of whether the capability data comprises an indication of support for dynamic backlight operation, wherein the video processor is arranged to compensate video data of the first video signal for the backlight dimming setting when operating in the first mode of operation but not when operating in the second mode of operation. This may allow improved compatibility and interoperability of the display system. Specifically, when a suitably equipped display panel unit is coupled to a suitably equipped control unit using e.g. a standardized interface (e.g. such as DisplayPort), a highly efficient and customized backlight control may be used. However, at the same time, the control unit may work with a display panel unit that does not have such functionality and may simply be coupled to this display panel unit using the standardized interface (e.g. such as a DisplayPort cable).

When operating in the second backlight mode the control unit may or may not calculate a backlight dimming setting.

In accordance with an optional feature of the invention, the means for transmitting the backlight indication is arranged to transmit the backlight indication in a data packet of a logical subchannel of the auxiliary data channel.

This may allow particularly advantageous performance in many embodiments and may in particular allow practical and low bandwidth backlight control using e.g. a standardized interface. In accordance with an optional feature of the invention, the control unit is arranged to compensate video data of the first video signal for the backlight setting.

This may allow particularly advantageous performance in many embodiments.

In accordance with an optional feature of the invention, the first video signal comprises pixel values for pixels of the display panel. This may allow particularly advantageous performance in many embodiments and may in particular reduce the required functionality in the display panel unit thereby allowing reduced resource usage, power consumption, complexity, cost and/or form factor of the display panel unit. The first video signal may specifically be an unencoded and/or uncompressed signal. Each pixel value may provide image information for one pixel of the display panel unit independently of other pixels in the display panel. The pixel values may specifically be RGB values or YP_BP_R values.

In accordance with an optional feature of the invention, the means for generating the first video signal is arranged to decode the input video signal to generate uncompressed video data for the first video signal.

This may allow particularly advantageous performance in many embodiments and may in particular reduce the required functionality in the display panel unit thereby allowing reduced resource usage, power consumption, complexity, cost and/or form factor of the display panel unit. The first video signal may specifically be an unencoded video signal. According to an aspect of the invention there is provided a method of operation for a display system including a display panel unit having an external input video connector and a control unit having an external output video connector, the display unit and control unit being coupled together by an interface connected to the external output video connector and to the external input video connector, the interface providing a main video data channel and an auxiliary data channel; the method comprising: the control unit performing the steps of: generating a first video signal for the display panel unit from an input video signal, transmitting the first video signal to the display panel unit using the main video data channel, determining a backlight dimming setting for the display panel unit in response to the input video signal, and transmitting a backlight indication indicative of the backlight dimming setting to the display panel unit in the auxiliary data channel; and the display panel unit performing the steps of: receiving the first video signal in the main video data channel, generating a display panel drive signal in response to the first video signal and feeding it to a display panel, receiving the backlight indication indicative in the auxiliary control data channel, and controlling a backlight parameter for the display panel in response to the backlight indication.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

Fig. 1 is an illustration of an example of a display system in accordance with some embodiments of the invention; Fig. 2 is an illustration of an example of a control unit for a display system in accordance with some embodiments of the invention; and

Fig. 3 is an illustration of an example of a display panel unit for a display system in accordance with some embodiments of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

The following description focuses on embodiments of the invention applicable to a display system comprising a Liquid Crystal Display (LCD) panel. However, it will be appreciated that the invention is not limited to this application but may be applied to many other display systems. Fig. 1 illustrates an example of a display system in accordance with some embodiments of the invention. The system comprises a control unit 101 coupled to a display panel unit 103 via an interface 105. Thus, in contrast to typical integrated display systems, the system of Fig. 1 employs a separation of functionality in a plurality of separate units. In particular, the display system of Fig. 1 uses a distribution of functionality that retains only a minimum of functionality in the display panel unit 103 which accordingly can be implemented with a reduced form factor and in particular can be implemented as a thinner display.

In the display system of Fig. 1, the control unit 103 comprises an external output video connector 107 which specifically may be a physical socket (or plug) providing electrical connections for a matching connector of an external video cable. Similarly, the display panel unit 103 comprises an external input video connector 109 which specifically may be a physical socket (or plug) providing electrical connections for a matching connector of the external video cable. Thus, in the example, the control unit 101 and the display panel unit 103 both comprise video connectors 107, 109 to which an external video cable can be connected. In the system, the control unit 101 is implemented in a box or enclosure and the external output video connector 107 may specifically be located on the surface of the box/enclosure such that it provides a connection between the internal functionality of the box/enclosure and functionality which is external to the box/enclosure. The external output video connector is specifically located such that it is manually accessible to a user. Similarly, the display panel unit 103 is implemented in a box or enclosure and the external input video connector 109 may specifically be located on the surface of the panel box/enclosure such that it provides a connection between the internal functionality of the panel box/enclosure and functionality which is external to the panel box/enclosure. The external input video connector is specifically located such that it is manually accessible to a user (without opening the enclosure).

In the system, the control unit 101 and display panel unit 103 are located in different enclosures. Specifically, the control unit 101 is remote from the display panel unit 103. Indeed, in typical use, the control unit 101 and the display panel unit 103 may be located with a distance between the closest points of their enclosures which is separated by e.g. more than 50 cm or 1 meter. Indeed, the control unit 101 and the display panel unit 103 are located such that they may be positioned completely independently of each other. For example, the display panel unit 103 may be positioned on a table top or on the wall whereas the control unit 101 may be located e.g. on a shelve of a different piece of furniture. As another example, the control unit 101 and the display panel unit 103 may be positioned in different rooms or in different areas of a room.

In the system, the control unit 101 and display panel unit 103 are thus coupled together by an external video interface cable which can be connected to the external output video connector 107 and the external input video connector 109. This external video interface cable is e.g. arranged to be manually connected and disconnected from the control unit 101 and the display panel unit 103 without requiring any enclosure to be opened. Thus, the external video connectors 107, 109 are accessible from outside the enclosures of respectively the control unit 101 and the display panel unit 103. The external video interface cable may be any suitable length for connecting the control unit 101 and the display panel unit 103 at their desired position, and may e.g. be more than 50cm or lmeter long. The external video interface cable may be the only connection between the control unit 101 and the display panel unit 103 (at least from a video perspective).

In the system, the control unit 101 may specifically be a television receiver. E.g. the control unit 101 may comprise functionality for receiving a digital or analog television signal and decoding this to generate a video signal. The control unit 101 may also comprise functionality for recording television signals and may for example be a Personal Video Recorder. Thus, in some embodiments, the system may provide a distributed television system. In some embodiments, the control unit 101 may be a computer. For example, the functionality of the control unit 101 may be implemented by software executed on a computer platform, such as e.g. a Personal Computer (PC). Such a PC may e.g. receive video programs from a network (e.g. a proprietary network or the Internet) and process this to generate a suitable video signal for display on the panel display unit 103.

Thus, in the system of Fig. 1, an external video interface 105 (specifically implemented using an external video cable) is used to support separate and/or individual and/or remote control unit 101 and display panel units 103.

In order to provide an efficient system, the distribution of the functionality between the control unit 101 and the display panel unit 103 is critical. Also the choice of what data to communicate across the interface 105 and how to communicate it is critical for the performance of the system. In order to minimize the functionality in the display panel unit 103, the video data that is communicated through the interface 105 in the system of Fig. 1 is directly pixel value data corresponding to the pixels of the LCD display panel of the display panel unit 103. Thus, the video signal communicated in the interface 105 directly provides the light settings for each pixel of the display and thus the display panel unit 103 can directly control the light of the individual pixel without having to decode or decompress the video signal. Specifically, the video signal may comprise luminance and possibly color data for each individual pixel. The luminance and possibly color data for a pixel is thus not dependent on any video data of the interface from any other pixel. Specifically, the interface video signal may comprise individual RGB or YP_BP_R values for each pixel.

In the specific example, the control unit 101 comprises one or more input video connectors (such as SCART or HDMI connectors) that may receive an encoded video signal such as an MPEG-2 or MPEG-4 encoded data signal. The control unit 101 then proceeds to decode the video signal to generate a stream of RGB pixel values that are communicated to the display panel unit 103 over the interface 105 via the external output video connector 107 and the external input video connector 109. Accordingly, the display panel unit 103 can with low complexity and resource usage generate a display panel drive signal containing the pixel values. Typically in conventional systems that implement a separate control unit, the interface to the display panel unit is a proprietary interface designed and optimized for the specific control unit, display panel unit and in particular for the specific display panel used. This may enable the control unit to control different aspects of the presented image and specifically makes it possible to include dedicated control connections and wires carrying specific control signals for the display panel.

However, the inventor has realized that an efficient display operation can be achieved without requiring a dedicated interface or indeed a proprietary interface with dedicated control signal connections and wires. Indeed, the inventor has realized that efficient display operation and performance can be achieved using a standardized display interface and specifically can be achieved using a DisplayPort display interface.

DisplayPort is a digital display interface standard that has been standardized by the Video Electronics Standards Association (VESA) (version 1.1a has been approved on January 11, 2008). The standard defines a new digital audio and video interconnect intended e.g. to be used between a computer and its display monitor, or a computer and a home-theatre system.

The DisplayPort connector supports 1, 2, or 4 data pairs in a Main Link (the main video data channel) which also carries clock and optional audio signals, each with a symbol rate of 1.62 or 2.7 Gbit/s. The video signal path supports 6 to 16 bits per color channel. A bi-directional auxiliary data channel (at a constant 1 Mbit/s) carries management and device control data for the Main Link

The DisplayPort video display interface has been designed as an efficient display interface that allows video sources, such as e.g. computers, to connect to a display using a single cable. However, the DisplayPort display interface has been standardized to provide a generic interface that allows any suitably equipped generic DisplayPort display to be coupled to any suitable DisplayPort source, such as any computer with a DisplayPort output. However, consequently, the DisplayPort standard does not take into account the control of other display operations that are dedicated to the specific display panel and which are typically considered to be part of the functionality of the display panel unit (e.g. of a monitor).

However, the inventor has realized that dedicated and improved display operation can be achieved by the display system of Fig. 1 even when using a standardized interface such as DisplayPort. The inventor has specifically realized that a particular problem when using such a standardized interface is the backlight control for the display panel.

Indeed, for some integrated displays, the effective backlight intensity is not static but rather is varied depending on the overall brightness of the image being displayed. For example, for a very bright scene, the maximum backlight intensity may be set with the LCD elements attenuating the light passing through the panel for darker areas. The same approach may be used for images with a large dynamic range. However, for dark images, the backlight intensity may be reduced with the attenuation by the LCD elements being reduced correspondingly thus resulting in the appropriate image. Thus, a dynamic backlight dimming or adjustment may be introduced that e.g. re-adjusts the backlight for each video frame. Such an approach may substantially reduce the power consumption for the display system and may increase the reliability and lifetime of the display panel.

The inventor has realized that backlight control is a particular problem in a distributed system with a separate control unit as the backlight determination is complex and therefore is ideally performed in the control unit yet is required to physically modify an operating characteristic (namely the intensity) of the display panel. Accordingly, dynamic backlight control is in conventional distributed systems not used or would typically require a dedicated and proprietary interface with additional connections carrying a signal controlling the backlight intensity.

However, the inventor has realized that dynamic backlight control can efficiently be supported in the system of Fig. 1 even if a standard interface such as DisplayPort is used. In particular, the inventor has realized that an efficient dynamic backlight control can be implemented by determining a suitable backlight setting (e.g. for each frame) and communicating this to the display panel unit 103 using the auxiliary data channel of the DisplayPort interface. Thus, in the system of Fig. 1, a distributed display system with efficient dynamic backlight control is implemented by communicating the video signal to the display panel unit 103 using the main channel of a DisplayPort interface and in parallel transmitting corresponding (dedicated and optionally proprietary) dynamic backlight data in the auxiliary channel of the DisplayPort interface despite this auxiliary channel not being synchronized to the main channel and being required to be compatible with generic DisplayPort monitors. Thus, the system allows a generic interface to be used to provide dedicated and improved support/optimization for a function that is dependent on specific characteristics of a specific display panel.

It will be appreciated that although the following discussion will focus on an application using a DisplayPort connection, other external video interfaces may be used in other embodiments. In particular, other standardized digital video interfaces may be used.

Such interfaces specifically include external video interfaces that either provide a main video data channel and an auxiliary data channel or which may be modified to do so. For example, other embodiments may use unmodified or modified digital video interfaces/connections such as a Digital Visual Interface (DVI); Serial digital interface (SDI); HDMI (High- Definition Multimedia Interface), IEEE1394 or similar.

Fig. 2 illustrates an example of the control unit 101 in more detail. The control unit 101 comprises a video processor 201 which receives an input video signal. The input video signal may be received from any source including an external or internal source. In the specific example, the video signal may be a moving image video signal but it will be appreciated that any signal representing one or more images that can be displayed may correspond to the input video signal, including e.g. still images, computer screen outputs etc. In the example, the video processor 201 receives an encoded/compressed video signal and proceeds to decode/decompress this to generate a decoded/uncompressed video signal. Specifically, the video processor 201 generates a video signal (henceforth referred to as the interface video signal) which contains individual RGB pixel values for each pixel of the display panel of the display panel unit 103.

The video processor 201 is coupled to a control main channel interface 203 which receives the interface video signal and transmits it to the display panel unit 103 on the main channel of the DisplayPort interface 105.

In addition, the control unit 101 comprises a backlight processor 205 which is coupled to the video processor 201. The backlight processor 205 receives the pixel values after the initial decoding of the input video signal. It then proceeds to determine backlight dimming setting for the video signal. For example, for each frame of the input video signal, the backlight processor 205 proceeds to identify the brightest pixel and to set the backlight to a level that corresponds to this brightness level. E.g. the backlight brightness level may be determined as the brightness that corresponds to the desired pixel brightness if no attenuation is performed by the liquid crystal elements of the display panel. The backlight dimming setting is then fed back to the video processor 201 which proceeds to compensate the decoded RGB values for this reduced backlight brightness. Specifically, the RGB values may be increased such that the LCD element attenuation is reduced by an amount corresponding to the reduction in the backlight brightness.

The backlight processor 205 is further coupled to a control auxiliary channel interface 207 which transmits a backlight indication representing the backlight dimming setting to the display panel unit 103 using the auxiliary data channel. Specifically, the control auxiliary channel interface 203 encodes the backlight dimming setting in accordance with a suitable data encoding format and then includes the resulting data in a data packet. The data packet is then communicated to the display panel unit 103 using a logical channel of the auxiliary channel of the DisplayPort interface. Specifically, the data packet is transmitted by addressing the data packet to a predetermined address that is not used for any other purpose.

The display panel unit 103 comprises a display main channel interface 301 and a display auxiliary channel interface 303 which interfaces the display panel unit 103 to the DisplayPort interface 105. Specifically, the display main channel interface 301 receives the data of the DisplayPort main channel and extracts the interface video signal. The received RGB pixel values together with any synchronization data is fed to a display driver 307 which is coupled to the display main channel interface 301. The display driver 307 is further coupled to a display panel 305 which in the specific example is an LCD display panel. The display driver 307 generates a display panel drive signal and feeds it to the display panel 305. Specifically, the RGB pixel values may be fed to the display panel 305 after conversion or reformatting to a format that is compatible with the specifications for the display panel 305. The display panel 305 then proceeds to adjust the attenuation of the individual liquid crystal elements such that the desired image is presented. The display auxiliary channel interface 303 receives the data of the

DisplayPort auxiliary channel and extracts the control data therefrom. In particular, the backlight indication data is extracted and fed to a backlight controller 309 coupled to the display auxiliary channel interface 303. In particular, the display auxiliary channel interface 303 may detect any data packets addressed to the specific predetermined address used by the control unit 101 for the backlight communication. The backlight indication data is then extracted from these data packets and fed to the backlight controller 309.

The backlight controller 309 is further coupled to the display panel 305 and is arranged to control the backlight of the display panel 305 in response to the backlight indication. Thus, the backlight controller 309 proceeds to determine the appropriate backlight setting (e.g. the backlight brightness or intensity) indicated by the backlight indication. The display panel 305 is then fed a parameter or control signal that results in the backlight being set to provide the desired characteristic (specifically the desired (time averaged) backlight intensity for a frame). In the specific example, a new backlight indication may be received for each frame and the backlight controller 309 thus proceeds to upgrade the backlight of the display panel 305 for each new frame.

The functionality required in the display panel unit 103 to perform these operations is very limited. Indeed, the backlight indication may directly represent the appropriate backlight parameter value which when fed to the display panel 305 results in the desired backlight setting. Furthermore, due to the use of a standardized interface the display main channel interface 301 and the display auxiliary channel interface 303 can be implemented by generally available low cost functionality.

Thus, the system of Fig. 1 provides a highly efficient and practical dynamic backlight control that reduces power consumption and improves image quality and reliability. Furthermore, this is achieved while implementing the majority of the complex backlight functionality in the control unit 101 and using a standard Display Port interface which does not have any inherent backlight support or provision. Thus, a very efficient system is achieved while at the same time employing a distributed implementation that may allow a very thin display panel unit 103 to be produced. In some embodiments, the backlight may directly be controlled by varying the intensity of the backlight and indeed the backlight processor 205 may calculate a desired dimmed backlight intensity and this may be forwarded to the backlight controller 309 which accordingly proceeds to dim the backlight in the display panel 305 accordingly.

However, in the example of Fig. 1, the backlight brightness is controlled by controlling a duty cycle for the backlight. Thus, rather than gradually dimming the instantaneous intensity of the backlight, the backlight is switched fully on and off with a duty cycle that corresponds to the desired average intensity. Typically, the duty cycle is controlled from between around 20% to around 100%.

Accordingly, the backlight processor 205 calculates a desired duty cycle for the backlight and transmits this to the backlight controller 309 via the backlight indication data in the auxiliary channel. In some scenarios, this can be fed directly to the display panel 305 which then proceeds to implement the desired duty cycle. In other embodiments, the backlight controller 309 may itself control the backlight by switching this on and off to provide the desired duty cycle. In the example, a new backlight duty cycle value is determined and set for each frame of the video signal. However, as the auxiliary channel of a DisplayPort interface is not synchronized with the main channel, the backlight controller 309 is arranged to synchronize the duty cycle of the backlight to the refresh rate of the panel. Specifically, the display panel 305 is refreshed when indicated by the vertical synchronization data of the main channel and the backlight controller 309 accordingly synchronizes the duty cycle backlight operation such that it matches that of the refresh rate indicated thereby.

It will be appreciated that the synchronization may be aimed at different levels of accuracy. For example, in some embodiments, the synchronization may simply ensure that a given duty cycle setting (which may be received prior to the video data for the frame it relates to) is applied to the correct frame. For example, the duty frame setting may be stored until the backlight controller 309 detects a vertical synch pulse in the video signal and may then proceed to apply it to the display panel 305.

In other embodiments, the synchronization may further align the duty cycle operation to the frame transitions. Specifically, the switching on (or off) of the backlight may be aligned with a vertical synch pulse. This may for example be achieved by synchronizing the duty cycle clock with the vertical synch/refresh rate of the video signal (e.g. using a phase locked loop).

Thus, a synchronization of the duty cycle backlight operation to the vertical synchronization of the display panel drive signal may be implemented in the backlight controller 309. This will typically improve image quality and will specifically reduce the perception of screen flicker that can result from the switching on and off of the backlight.

In some embodiments, the display panel may be arranged to receive video data in the same format as is generated by the video processor 201 and specifically in the same format as is communicated over the interface 105. In such embodiments, the display driver 307 can directly forward the received video data to the display panel 305.

However, in many embodiments, the data format of the interface video signal may not be the same as that which is required by the display panel 305. In particular, most display panels are manufactured with a display interface that requires input video (pixel) data in accordance with a Low- Voltage Differential Signalling (LVDS) video signal format. This LVDS video signal format may be specified by the display panel manufacturer and may be proprietary. However, the DisplayPort interface requires video data in the form of RGB pixel data which may not directly be compatible with the LVDS data format for the data panel 305. In such embodiments, the display driver 307 may be arranged to perform the conversion between the two video signal formats.

In the specific example, the display panel 305 requires video input in the form of an LVDS signal that provides data in a specific format. Specifically, the display panel 305 requires an RGB value for each pixel but furthermore requires the data bits of each individual bit to be provided in a serial format in a specific order. Accordingly, the display driver 307 may convert e.g. 8 or 10 bit RGB values of the DisplayPort into suitable bit sequences that are provided to the display panel 305 on its LVDS input interface.

In the example, the display driver 307 and the backlight controller 309 (as well as optionally the display main channel interface 301 and the display auxiliary channel interface 303) are implemented in a single integrated circuit. Specifically, simple digital circuitry providing the required functionality for the generation of the backlight control signal and the display driver signal can be designed and implemented in a single Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC). Such an integrated solution may provide a particular efficient implementation with reduced power consumption, increased reliability and reduced form factor for the display panel unit 103. Furthermore, it may provide a very cost effective implementation.

In the system of Fig.1 the control unit 101 and display panel unit 103 are arranged such that they are compatible with other DisplayPort equipped devices. Specifically, any image source providing a DisplayPort output can be coupled to the display panel unit 103 and the control unit 101 can be coupled to any DisplayPort display or monitor.

In particular, the control unit 101 is arranged to detect if it is coupled to a matching display panel unit that supports dynamic remote backlight control. If not, the control unit 101 switches to a non-dynamic backlight mode wherein no dynamic backlight control is used. Thus, in this case, the RGB pixel value data of the interface video signal is not compensated for the backlight dimming but rather covers the full dynamic range of the image assuming a static full intensity backlight setting.

Similarly, the display panel unit 103 is arranged to detect if it is coupled to a matching control unit that provides dynamic remote backlight control. If not, the display panel unit 103 switches to a non-dynamic backlight mode of operation wherein no dynamic backlight control is used. Thus, in this case, the RGB pixel value data of the interface video signal is assumed to correspond a fixed backlight setting and thus a constant (maximum) backlight intensity is set by the backlight controller 309.

Specifically, the display panel unit 103 is arranged to transmit capability data over the auxiliary control data channel of the DisplayPort interface. The capability data defines what capabilities the display panel unit 103 provides. This information includes an indication of a support for dynamic backlight dimming since the display panel unit 103 is capable of supporting such operation (and may e.g. include a specification of associated parameters such as e.g. an allowable duty cycle range, an address to be used for the data packets etc). Thus, when the control unit 101 is connected to a new display panel unit, it receives the capability data therefrom. If this data includes an indication of support for dynamic backlight dimming (as is the case if the new display panel unit is the display panel unit 103 of Figs. 1 and 3), it proceeds to operate in the backlight mode of operation wherein the RGB data of the main channel is compensated for the reduced backlight and a backlight duty cycle indication is transmitted on the auxiliary channel. However, if no such data is received (e.g. because a standard conventional monitor is coupled to the control unit 101), the control unit 101 enters a non-backlight dimming mode of operation and transmits noncompensated RGB data. Furthermore, in this case, the control unit 101 may not calculate or transmit any backlight data.

Similarly, the control unit 101 is arranged to transmit capability data over the auxiliary control data channel of the DisplayPort interface defining the capabilities of the control unit 101. This information includes an indication of the support for dynamic backlight dimming. Thus, when the display panel unit 103 is connected to a new control unit, it receives the capability data therefrom. If this data includes an indication of support for dynamic backlight dimming (as is the case if the new control unit is the control unit 101 of Figs. 1 and 2), it proceeds to operate in the backlight mode of operation wherein the RGB data of the main channel is assumed to be compensated for a backlight setting/dimming. Furthermore, the backlight indication, and specifically a backlight duty cycle indication, is received from the auxiliary channel and used to control the duty cycle of the backlight. However, if no such data is received, the control unit enters a non-backlight dimming mode of operation wherein a constant backlight is employed (e.g. the backlight is switched permanently on at the highest intensity). Thus, the approach allows control units and display panel units that support dynamic backlight dimming to fully support the DisplayPort interface. In particular, it allows the control and display system units to be used with any complementary DisplayPort equipped unit whether this is capable of supporting dynamic backlight dimming or not. Thus, images can be displayed correctly when the control unit 101 or the display panel unit 103 are not used together but with conventional DisplayPort equipped units. However, when two units are coupled together that both support dynamic backlight dimming, this is automatically detected by the units and the operation is automatically modified to provide the associated improved performance.

It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors.

However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims do not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example shall not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS:

1. A display system comprising: a display panel unit (103) having an external input video connector (109); and a control unit (101) having an external output video connector (107), the display unit (103) and control unit (101) being arranged to be coupled together by an interface (105) connected to the external output video connector and to the external input video connector, the interface providing a main video data channel and an auxiliary data channel; wherein the control unit (101) comprises: means (201) for generating a first video signal for the display panel unit from an input video signal, means (203) for transmitting the first video signal to the display panel unit (103) using the main video data channel, means (205) for determining a backlight dimming setting for the display panel unit (103) in response to the input video signal, and - means (207) for transmitting a backlight indication indicative of the backlight dimming setting to the display panel unit (103) in the auxiliary data channel; and the display panel unit (103) comprises: a display panel (305), means (301) for receiving the first video signal in the main video data channel, - a display driver (307) for generating a display panel drive signal in response to the first video signal and feeding it to the display panel (305), means (303) for receiving the backlight indication in the auxiliary data channel, and a backlight controller (309) for controlling a backlight characteristic for the display panel (305) in response to the backlight indication.

2. The display system of claim 1 wherein the backlight setting is a backlight duty cycle setting.

3. The display system of claim lwherein the backlight controller (309) is arranged to synchronize a duty cycle of the backlight to a vertical synchronization of the display panel drive signal.

4. The display system of claim 1 wherein the main video data channel and the auxiliary data channel are not synchronized and the backlight controller (309) is arranged to synchronize a duty cycle of the backlight to a vertical synchronization of the first video signal.

5. The display system of claim 1 wherein the interface is a DisplayPort interface.

6. The display system of claim 1 wherein the display driver (307) comprises a conversion processor for converting the first video signal from a first video signal format to a second video signal format of the display panel drive signal.

7. The display system of claim 6 wherein the first video format is a DisplayPort video signal format and the second video signal format is a Low- Voltage Differential Signalling video signal format.

8. The display system of claim 1 wherein the display driver (307) and the backlight controller (309) are implemented in a single integrated circuit.

9. The display system of claim 1 wherein the display panel unit (103) further comprises: - means for receiving capability data via the auxiliary data channel, the capability data being indicative of capabilities of a unit providing the capability data; means for switching between a first backlight mode and a second backlight mode of operation in response to a determination of whether the capability data comprises an indication of support for dynamic backlight operation, wherein the backlight controller (309) is arranged to change the backlight parameter in response to the backlight indication when operating in the first mode of operation but not when operating in the second mode of operation.

10. The display system of claim 1 wherein the control unit (101) further comprises: means for receiving capability data via the auxiliary data channel, the capability data being indicative of capabilities of a unit providing the capability data; - means for switching between a first backlight mode and a second backlight mode of operation in response to a determination of whether the capability data comprises an indication of support for dynamic backlight operation, wherein the video processor (201) is arranged to compensate video data of the first video signal for the backlight dimming setting when operating in the first mode of operation but not when operating in the second mode of operation.

11. The display system of claim 1 wherein the means (207) for transmitting the backlight indication is arranged to transmit the backlight indication in a data packet of a logical subchannel of the auxiliary data channel.

12. The display system of claim 1 wherein the control unit (101) is arranged to compensate video data of the first video signal for the backlight setting.

13. The display system of claim 1 wherein the first video signal comprises pixel values for pixels of the display panel (305).

14. The display system of claim 1 wherein the means (201) for generating the first video signal is arranged to decode the input video signal to generate uncompressed video data for the first video signal.

15. A method of operation for a display system including a display panel unit (103) having an external input video connector (109) and a control unit (101) having an external output video connector (107), the display unit (103) and control unit (101) being coupled together by an interface connected to the external output video connector and to the external input video connector, the interface providing a main video data channel and an auxiliary data channel; the method comprising: the control unit (101) performing the steps of: generating a first video signal for the display panel unit from an input video signal, transmitting the first video signal to the display panel unit (103) using the main video data channel, determining a backlight dimming setting for the display panel unit (103) in response to the input video signal, and transmitting a backlight indication indicative of the backlight dimming setting to the display panel unit (103) in the auxiliary data channel; and the display panel unit (103) performing the steps of: receiving the first video signal in the main video data channel, generating a display panel drive signal in response to the first video signal and feeding it to a display panel (305), receiving the backlight indication indicative in the auxiliary control data channel, and controlling a backlight parameter for the display panel (305) in response to the backlight indication.