WO2006038194A1

WO2006038194A1 - Transflective liquid crystal display device

Info

Publication number: WO2006038194A1
Application number: PCT/IB2005/053275
Authority: WO
Inventors: Stephen J. Battersby; Jason R. Hector
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2004-10-08
Filing date: 2005-10-05
Publication date: 2006-04-13
Anticipated expiration: 2007-04-08
Also published as: TW200630690A; GB0422350D0

Abstract

A transfiective display device, comprising an array of transmissive pixels (4a-4I; 204a-204d) and reflective pixels (12a-12d; 212); wherein the array comprises a different number of transmissive pixels (4a-4I; 204a-204d) compared to reflective pixels arranged such that the resolution of an image displayed in transmissive mode is different to the resolution of a corresponding image displayed in reflective mode. For example, the resolution of an image displayed in transmissive mode is greater than the resolution of a corresponding image displayed in reflective mode. In some embodiments each transmissive pixel (4a-4I) comprises a transmissive aperture (8) surrounded by a coloured reflective sub-pixel (6) and the device further comprises means for displaying different colours to the transmissive pixel (4a-4I) by colour sequential driving. In other embodiments, each transmissive pixel (204a-204d) comprises a plurality of differently coloured transmissive sub-pixels (203a-203I).

Description

DESCRIPTION

TRANSFLECTIVE LIQUID CRYSTAL DISPLAY DEVICE

The present invention relates to liquid crystal display (LCD) devices, and more particularly, to transflective LCD devices.

Transmissive liquid crystal display (LCD) devices and reflective LCD devices have been known for many years. In transmissive LCD devices, a backlight behind the liquid crystal layer provides the light which is modulated by the liquid crystal layer to provide an image for a user viewing the LCD device. In reflective LCD devices, ambient light falling on the front of the reflective LCD device provides the light which is modulated by the liquid crystal layer to provide an image for a user viewing the LCD device. More recently, transflective LCD devices have been provided.

Transflective LCD devices provide a combined operation of a transmissive mode using light from a backlight behind the liquid crystal layer and a reflective mode using ambient light falling on the front of the LCD device.

As in conventional reflective or transmissive LCD devices, typical transflective LCD devices comprise a plurality of pixels arranged in an array of rows and columns. Each pixel comprises a green sub-pixel, a red sub-pixel and a blue sub-pixel. Each sub-pixel is provided with an opaque reflective electrode (or electrode and reflector layered arrangement) and a transparent transmissive electrode. An aperture is provided in the reflective electrode such that light from the backlight can pass through the aperture area of the sub- pixel so as to exit the device so as to provide the transmissive mode of operation for the sub-pixel. Ambient light is reflected from the reflective electrode area of the sub-pixel (i.e. broadly speaking, the sub-pixel area except for the aperture area) so as to provide the reflective mode of operation of the sub-pixel. Examples of colour transflective LCD devices are described in US 6,501 ,519 and US 6,734,935. Display applications are requiring ever increasing resolution, e.g. upwards of 100 pixels per cm in the case of a transflective LCD device for use in modern mobile telephones. This trend is expected to continue as products such as mobile telephones become more sophisticated in their video display requirements and so on. However, increased resolution means the size of each pixel is reduced, and in the case of conventional transflective LCD devices this means the transmissive aperture must become very small and hence require high power consumption for an acceptable brightness, and/or a only a reduced brightness compared to lower resolution devices would be provided.

Various approaches have been described for improving fabrication processes so that available space is optimised, but such approaches tend to involve costlier or more complicated fabrication processes. Furthermore, such approaches can inherently only improve matters to a certain extent limited by the fundamental pixel area limits imposed on the reflective part of the pixel area and the transmissive aperture respectively by the level of resolution required.

Another approach known in the field of transmissive LCD devices, as opposed to transflective LCD devices, is to provide the different colours i.e. red, green and blue, from a single pixel area (as opposed to respective sub- pixels) by means of a colour sequential driving approach. A transmissive light source is switched temporally between red, green and blue (instead of being a white light source). Thus only one common pixel area is required rather than three sub-pixel areas for each pixel. An example of a colour sequential LCD device is described in US 5,128,782. Use of a colour sequential approach in a transflective LCD device might therefore alleviate size reduction problems associated with increased resolution in transflective LCD devices. However, to maintain the resolution of the reflective mode of operation, the reflective mode has to operate in monochrome. Furthermore, the colour sequential requires relatively complex driving techniques, and more complicated light sources and control thereof. The present inventors have realised that the various problems discussed above derive, at least to some extent, from the fact that in conventional transflective LCD devices the resolution provided by the transmissive mode is the same as the resolution provided by the reflective mode. The present inventors have further realised that by breaking this conventional link between the respective resolution in the reflective mode and the transmissive mode, the various size reduction problems described above tend to be alleviated, and/or various new design routes that can provide further advantages are made possible.

The present inventors have further realised that when breaking this conventional link between the respective resolution in the reflective mode and the transmissive mode by providing a lower resolution in reflective mode compared to transmissive mode, the tendency to alleviate the size reduction problems and/or allow new design routes with associated advantages can be achieved whilst at the same time tending to cause only a limited or no detraction in perceived performance to the viewer, by virtue of the aspect that the image quality in reflective mode is anyway expected to be less than that in transmissive mode and is not usually expected to provide such high quality display performance as is expected from the transmissive mode, particularly when displaying applications for which the increased resolution is particularly required.

The present invention provides a transflective display device, comprising: an array of transmissive pixels and reflective pixels; wherein the array comprises a different number of transmissive pixels compared to reflective pixels arranged such that the resolution of an image displayed in transmissive mode is different to the resolution of a corresponding image displayed in reflective mode.

The array may comprise more transmissive pixels than reflective pixels such that the resolution of an image displayed in transmissive mode is greater than the resolution of a corresponding image displayed in reflective mode. In many applications this provides better resolution where this is most of benefit, i.e. transmissive mode, at a trade off with loss of resolution where resolution is not so significant, i.e. reflective mode. There may be four times as many of one of transmissive or reflective pixels as there are of the other of transmissive or reflective pixels. This allows standard driving software to be used, as this is typically scaled in factors of four.

Each reflective pixel may comprise a plurality of differently coloured reflective sub-pixels, with each colour reflective sub-pixel of a reflective pixel being associated with a respective transmissive pixel.

Each reflective pixel may comprise a red reflective sub-pixel, a green reflective sub-pixel, a blue reflective sub-pixel and a white reflective sub-pixel.

This is particularly convenient for providing a one quarter resolution in reflective mode compared to transmissive mode by providing one such reflective sub-pixel for each transmissive pixel.

The reflective sub-pixels of a given pixel may be arranged over at least two rows and two columns of the array. This arrangement (as opposed to positioning all the sub-pixels of a given reflective sub-pixel across a single row) in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user.

Separate thin film transistors may be provided for the reflective pixels and the transmissive pixels. This allows the transmissive mode and reflective modes to be driven with different data.

Thin film transistors may be shared between the reflective pixels and the transmissive pixels. This reduces component count and driving requirements.

In some aspects of the invention, each transmissive pixel comprises a transmissive aperture surrounded by a coloured reflective sub-pixel; and the device further comprises means for displaying different colours to the transmissive pixel by colour sequential driving.

In other aspects of the invention, each transmissive pixel comprises a plurality of differently coloured transmissive sub-pixels. The array may comprise differently coloured transmissive sub-pixels arranged adjacently along rows to provide transmissive pixels, and differently coloured reflective sub pixels interspersed, along the rows, between the transmissive pixels.

Rows of transmissive sub-pixels may alternate with rows of reflective sub-pixels.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional illustration (not to scale) of part of a transflective LCD device;

FIG. 2 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels in the transflective LCD device of FIG. 1 ;

FIG. 3 is a schematic diagram showing the arrangement of reflective colour pixels in the transflective LCD device of FIG. 1 ; FIG. 4 is a schematic diagram showing in simplified form the driving connections employed in the transflective LCD device of FIG. 1;

FIG. 5 is a schematic diagram showing in simplified form the driving connections employed in another transflective LCD device;

FIG.6 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels and driving connections in another transflective LCD device in which the resolution in the reflective mode is one quarter that in the transmissive mode;

FIG. 7 is a schematic diagram showing the arrangement of reflective colour pixels in the transflective LCD device of FIG. 6; FIG. 8 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels and driving connections in another transflective LCD device in which the resolution in the reflective mode is one quarter that in the transmissive mode;

FIG. 9 is a schematic diagram showing the arrangement of sub-pixels in a transflective LCD device with differently coloured transmissive sub-pixels; FIG. 10 is a schematic diagram showing the arrangement and layout of four transmissive colour pixels and their associated single reflective colour pixel as provided by the sub-pixels of FIG. 9;

FIG. 11 is a schematic diagram showing in simplified form the driving connections in the transflective LCD device of FIGS. 9 and 10; FIG. 12 is a schematic diagram showing in simplified form the driving connections employed in another transflective LCD device;

FIG. 13 is a schematic diagram showing in simplified form the driving connections employed in another transflective LCD device;

FIG. 14 is a schematic diagram showing the arrangement and layout of sub-pixels and pixels of further transflective LCD devices; and

FIG. 15 is a schematic diagram showing the arrangement and layout of sub-pixels and pixels of further transflective LCD devices.

In conventional colour transmissive or reflective LCD devices, each pixel comprises a plurality of colour sub-pixels, typically red, green and blue. In conventional transflective LCD devices, each transmissive pixel comprises a plurality of colour sub-pixels and each reflective pixel comprises a plurality of colour sub-pixels; furthermore each colour sub-pixel of the transmissive pixel corresponds to the same colour sub-pixel of the reflective pixel. However, in the transflective LCD device of the first embodiment of the present invention, the different colours are provided for the transmissive pixels by virtue of the backlight being driven in a colour sequential mode, hence there are no colour transmissive sub-pixels, only transmissive pixels. On the other hand, each reflective pixel does comprise three (red, green and blue) sub-pixels. In this embodiment each reflective sub-pixel is associated with a respective transmissive pixel, i.e. three transmissive pixels are provided for each reflective pixel, with each transmissive pixel being associated with a single colour reflective sub-pixel. For convenience, a transmissive pixel along with its associated reflective colour sub-pixel will hereinafter be termed a transmissive pixel/reflective sub-pixel.

FIG. 1 is a schematic cross-sectional illustration (not to scale) of part of a transflective LCD device according to a first embodiment.

The transflective LCD device has a large number of transmissive pixels 4 arranged in conventional manner in an array of rows and columns, in this example 150 rows by 500 columns. The transflective LCD device further comprises a plurality of reflective colour sub-pixels, each associated with and substantially surrounding a respective one of the transmissive pixels. For clarity, only one transmissive pixel/reflective sub-pixel 2 is shown in FIG. 1.

The transmissive pixel/reflective sub-pixel 2 comprises a first approximately central area which effectively constitutes the transmissive pixel 4 and an area surrounding the central area which effectively constitutes the reflective sub-pixel 6.

The transflective LCD device has a lower substrate 110 and an upper substrate 160 facing apart from each other. A first passivation layer 120 is formed on the inner surface of the lower substrate 110, and the first passivation layer 120 has a first transmissive hole 122 in the area corresponding to the transmissive pixel 4. A transmissive electrode 130 of a transparent conductive material is formed on the first passivation layer 120.

Next, a second passivation layer 140 is formed on the transmissive electrode

130, and a reflective electrode 150 is formed on the second passivation layer

140. The reflective electrode 150 has a second transmissive hole 152 exposing the transmissive electrode 130 on the first transmissive hole 122.

A thin film transistor (TFT) (not shown) is formed on the inner surface of the lower substrate 110, and the TFT is connected electrically to the transmissive electrode 130 and the reflective electrode 150.

A colour filter layer 161 is formed on the inner surface of the upper substrate 160 and a common electrode 162 is formed on the colour filter 161 layer. In the area of the transmissive pixel 4, the colour filter layer 161 is transparent, providing a transparent window 164 which does not affect the colour of the light transmitted through it. In the area of the reflective sub-pixel 6, the colour filter layer 161 is coloured to provide the conventional colour filter 166 of the reflective sub-pixel, i.e. red, green or blue as will be explained in more detail below. Next, retardation films 171 and 172 are arranged on the outer surface of the lower and upper substrates 110 and 160, respectively. Polarizers 181 and 182 are arranged on the outer surface of the respective retardation film 171 and 172.

A backlight 190 is located under the lower polarizer 181 and extends over the whole array of pixels; however this is shown schematically in FIG. 1 as being specifically under the sub-pixel 2. The backlight is one which can be driven sequentially in different colours, here red, green and blue. Any suitable colour sequential backlight and corresponding driver apparatus may be employed. In this example, apparatus such as that described in US 5,128,782, the contents of which are contained herein by reference, is used.

A liquid crystal layer 200 is disposed between the reflective electrode 150 and the common electrode 162. The liquid crystal molecules of the liquid crystal layer 200 are arranged horizontally with respect to the substrates 110 and 160. The liquid crystal layer 200 has a positive permittivity anisotropy value, so the liquid crystal molecules are arranged parallel to a direction of the electric field induced between the reflective electrode 150 and the common electrode 162 when voltage is applied to the electrodes 130, 150 and 162.

A phase difference of the liquid crystal layer depends on the refractive index anisotropy value (An) and the thickness (d) of the liquid crystal layer. Therefore, the phase difference of the liquid crystal layer can be controlled by changing the thickness of the liquid crystal layer.

Accordingly, as shown in FIG. 1, the first passivation layer 120 has a first transmissive hole 122 so that the brightness in the transmissive mode and the reflective mode may be made uniform. In this example the liquid crystal layer 200 in the transmissive region 4 has twice the thickness of the liquid crystal layer 200 in the reflective region 6. The first transmissive hole 122 and the second transmissive hole 152 together effectively provide a transmissive aperture 8 that allows the transmissive mode of operation of the transmissive pixel 4 with the backlight 190 as the transmissive light source. FIG. 2 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels 2 in the transflective LCD device of this embodiment. Twelve transmissive pixel/reflective sub-pixels 2a-2l, each of the form of the transmissive pixel/reflective sub-pixel 2 described above with reference to FIG.1, are shown by way of example, i.e. each transmissive pixel/reflective sub-pixel 2a-2l comprises a respective transmissive pixel 4a-4l and a respective reflective colour sub-pixel 6a-6l. The transmissive pixel/reflective sub-pixels 2a-2l are arranged in rows and columns. In more detail, transmissive pixel/reflective sub-pixels 2a-2d are in a first row, transmissive pixel/reflective sub-pixels 2e to 2h are in a second row directly under the first row, and transmissive pixel/reflective sub-pixels 2i-2l are in a third row directly under the second row; hence transmissive pixel/reflective sub-pixels 2a, 2e and 2i are in a first column, transmissive pixel/reflective sub-pixels 2b, 2f and 2j are in a second column next to the first column, transmissive pixel/reflective sub-pixels 2c, 2g and 2k are in a third column next to the second column, and transmissive pixel/reflective sub-pixels 2d, 2h and 21 are in a fourth column next to the third column.

The colours of the reflective colour sub-pixels 6a-6l are arranged as follows. The first sub-pixel in the first row, i.e. sub-pixel 6a is red, and the next sub-pixel in the first row, i.e. sub-pixel 6b is green. This alternation between red and green is continued across the row, i.e. the next sub-pixel in the first row, i.e. sub-pixel 6c is red, the next sub-pixel in the first row i.e. sub-pixel 6d is green, and so on. Turning now to the second row, the first sub-pixel in the second row, i.e. sub-pixel 6e is blue, and the next sub-pixel in the second row, i.e. sub-pixel 6f is red. This alternation between blue and red is continued across the row, i.e. the next sub-pixel in the second row, i.e. sub-pixel 6g is blue, the next sub-pixel in the second row i.e. sub-pixel 6h is red, and so on. Turning now to the third row, the first sub-pixel in the third row, i.e. sub-pixel 6i is green, and the next sub-pixel in the third row, i.e. sub-pixel 6j is blue. This alternation between green and blue is continued across the row, i.e. the next sub-pixel in the third row, i.e. sub-pixel 6k is green, the next sub-pixel in the third row i.e. sub-pixel 6I is blue, and so on. The reflective colour sub-pixels are arranged as described in the preceding paragraph so as to provide an efficient layout of reflective colour pixel, as will now be described with reference to FIG. 3. FIG. 3 is a schematic diagram showing the arrangement of reflective colour pixels 12a-12d in the transflective LCD device of this embodiment. Each reflective colour pixel 12a- 12d comprises one red, one green and one blue reflective colour sub-pixel of the above described sub-pixels 6a-6l (in FIG. 3 the outline of the reflective colour pixels is shown in bold line, whereas the distinction between respective reflective colour sub-pixels is shown in dashed line). In each pixel, two sub- pixels are from a given row and the third sub-pixel is from an adjoining row. In more detail, a first reflective colour pixel 12a comprises the first (red) sub-pixel 6a of the first row, the adjacent green sub-pixel 6b of the first row, and the first (blue) sub-pixel 6e of the second row which is furthermore in the same column (the first column) as the first (red) sub-pixel 6a. A second reflective colour pixel 12b comprises the second sub-pixel of the second row, i.e. the red sub-pixel 6f, and the first and second sub-pixels of the third row, i.e. the green sub-pixel 6i and the blue sub-pixel 6j. It can be seen that these two pixels 12a and 12b form an interlocking pattern. This pattern is repeated throughout the array, for example as shown in FIG. 3, a third reflective colour pixel 12c comprises the third and fourth sub-pixels of the first row, i.e. the red sub-pixel 6c and the green sub-pixel 6d, and the third sub-pixel of the second row, i.e. the blue sub- pixel 6g; and a fourth reflective colour pixel 12d comprises the fourth sub-pixel of the second row, i.e. the red sub-pixel 6h, and the third and fourth sub-pixels of the third row, i.e. the green sub-pixel 6k and the blue sub-pixel 6I. This arrangement (as opposed to positioning all the four sub-pixels of a given reflective sub-pixel across a single row) in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user. Returning to FIG. 2, the TFT of each transmissive pixel/reflective sub- pixel mentioned (but not shown) with respect to FIG. 1 is shown schematically in FIG. 2 as a respective TFT 10 located at each transmissive pixel/reflective sub-pixel 2a-2l, i.e. in this embodiment a single TFT 10 is shared by the transmissive pixel part and the reflective sub-pixel part of each transmissive pixel/reflective sub-pixel 2, by virtue of the TFT 10 being electrically connected to both transmissive electrode 130 and the reflective electrode 150 as described earlier with reference to FIG. 1, and which will be described in more detail with reference to FIG. 4 below. Other details of the transflective LCD device, except where otherwise stated in relation to the use of the colour sequential backlight, the association of reflective colour sub-pixels with transmissive pixels, and the driving thereof, may be as per any conventional transflective LCD device, and are in the present embodiment, and other embodiments herein described, the same as, and operate the same as, the transflective LCD device disclosed with reference to FIG. 2 of US 6,734,935, the contents of which are contained herein by reference.

FIG. 4 is a schematic diagram showing in simplified form the driving connections employed in the transflective LCD device of this embodiment. A column driver 14 is connected to the TFTS 10 via column conductors 16a-16d, each column conductor 16a-16d being connected to each of the TFTs 10 of a respective column of transmissive pixel/reflective sub-pixels 2a-2l. A row driver 18 is connected to the TFTS 10 via row conductors 20a-16c, each row conductor 20a-20c being connected to each of the TFTs 10 of a respective row of transmissive pixel/reflective sub-pixels 2a-2l. In operation, the row driver 18 selects one row of transmissive pixel/reflective sub-pixels 2a-2l at a time, and the column driver provides data signal levels to the columns in synchronisation therewith. Thus in this embodiment, the row driver 18 carries out the row selection driving for both the transmissive mode and the reflective mode of operation such that the transmissive pixels and reflective sub-pixels are driven with the same data as each other, i.e. provide the same images but of different resolution. In the arrangement described above with reference to FIGs. 1-4 the resolution of the transmissive mode is three times that of the reflective mode. By implementing this differing resolution between the modes it is possible to provide full colour display in the reflective mode as well as the transmissive mode, whilst making full use of the three-fold increase in resolution offered in the transmissive mode by use of the colour sequential driving approach. This is surprisingly beneficial, inter alia because of the realisation by the present inventor that such improved resolution is primarily desired in the transmissive mode as opposed to in the reflective mode. The same type of benefit can be achieved with other driving/connection arrangements, for example that which will now be described with reference to FIG. 5.

FIG. 5 is a schematic diagram showing in simplified form the driving connections employed in a transflective LCD device of a further embodiment. In this embodiment, the transflective LCD device is the same as that described above in the first embodiment, except for the provision of additional TFTs, different row drivers, and different row conductors, as will now be explained in more detail. In this embodiment, as shown in FlG. 5, in addition to the earlier described TFTs 10 which in this embodiment are provided for just the reflective sub-pixels 6a-6l (i.e. a respective TFT 10 is provided for each reflective sub- pixel 6a-6I by virtue of each respective TFT 10 being electrically connected to a respective reflective electrode 150), a respective TFT 11 is provided for each transmissive pixel 4a-4l by virtue of each respective TFT 11 being electrically connected to a respective transmissive electrode 130.

Furthermore, separate row drivers are provided for driving the TFTs 10 of the reflective sub-pixels 6a-6l compared to the TFTs 11 of the transmissive pixels 4a-4l. In more detail, a reflective mode row driver 22 is connected to the reflective sub-pixel TFTS 10 via reflective mode row conductors 24a-24c, and a separate transmissive mode row driver 26 is connected to the transmissive pixels 4a-4l via separate transmissive mode row conductors 28a-28c. In operation the use of separate row drivers 22 and 26 for the reflective mode and transmissive mode respectively allows the transmissive pixels to be driven with different data compared to the reflective sub-pixels, i.e. provide separate images which may be adapted to suit the respective differing resolutions.

In the above embodiments, the resolution in reflective mode is one third that in the transmissive mode, i.e. there are three times as many transmissive pixels as there are reflective pixels. Further embodiments will now be described, with reference to FIGS. 6-8, in which the resolution in reflective mode is one quarter that in the transmissive mode, i.e. there are four times as many transmissive pixels as there are reflective pixels. This is achieved by providing four "colours" of reflective sub-pixel, i.e. red, green, blue and white, i.e. a white sub-pixel is added to the red, green and blue sub-pixles of the previous embodiments. An advantage of such embodiments is that they are particularly convenient to use with common driving software and arrangements, which typically are provided in resolutions which are scaled by a factor of four. FIG.6 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels 2 and driving connections in the transflective LCD device of a first embodiment in which the resolution in the reflective mode is one quarter that in the transmissive mode. In this embodiment, the transflective LCD device is the same as that of the embodiment described above with respect to FIGS. 2, 3 and 4, and the same reference numerals are used for the same elements, except for the arrangement of the colours of the reflective colour sub-pixels 6a-6h (only 8 sub-pixels are shown by way of example in FIG. 6), and their grouping into reflective pixels, as will now be explained in more detail. The colours of the reflective colour sub-pixels 6a-6h are arranged as follows. The first sub-pixel in the first row, i.e. sub-pixel 6a is red, and the next sub-pixel in the first row, i.e. sub-pixel 6b is green. This alternation between red and green is continued across the row, i.e. the next sub-pixel in the first row, i.e. sub-pixel 6c is red, the next sub-pixel in the first row i.e. sub-pixel 6d is green, and so on. Turning now to the second row, the first sub-pixel in the second row, i.e. sub-pixel 6e is blue, and the next sub-pixel in the second row, i.e. sub-pixel 6f is white. This alternation between blue and white is continued across the row, i.e. the next sub-pixel in the second row, i.e. sub-pixel 6g is blue, the next sub-pixel in the second row i.e. sub-pixel 6h is white, and so on. This arrangement is continued for further rows, i.e. the third row comprises alternating red and green sub-pixels, the further row comprises alternating blue and white sub-pixels, and so on.

The reflective colour sub-pixels are arranged as described in the preceding paragraph so as to provide an efficient layout of reflective colour pixel with a resolution one quarter that of the transmissive pixels, as will now be described with reference to FIG. 7. FIG. 7 is a schematic diagram showing the arrangement of reflective colour pixels 12a and 12c in the transflective LCD device of this embodiment. Each reflective colour pixel 12a, 12c comprises one red, one green, one blue and one white reflective colour sub- pixel of the above described sub-pixels 6a-6h (in FIG. 7 the outline of the reflective colour pixels is shown in bold line, whereas the distinction between respective reflective colour sub-pixels is shown in dashed line). In each pixel, two sub-pixels are from a given row and the other two sub-pixels are from an adjoining row. In more detail, a first reflective colour pixel 12a comprises the first (red) sub-pixel 6a of the first row, the adjacent green sub-pixel 6b of the first row, the first (blue) sub-pixel 6e of the second row which is in the same column (the first column) as the first (red) sub-pixel 6a, and the first (white) sub-pixel 6e of the second row which is in the same column (the first column) as the first (red) sub-pixel 6a. A second reflective colour pixel 12c comprises the third and fourth sub-pixels of the first row, i.e. the red sub-pixel 6c and the green sub-pixel 6d, and the third and fourth sub-pixels of the second row, i.e. the blue sub-pixel 6g and the white sub-pixel 6h. This pattern is repeated throughout the array. This arrangement (as opposed to positioning all the four sub-pixels of a given reflective sub-pixel across a single row) in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user.

Returning to FIG. 6, in this embodiment a single TFT 10 is shared by the transmissive pixel part and the reflective sub-pixel part of each transmissive pixel/reflective sub-pixel 2, by virtue of the TFT 10 being electrically connected to both transmissive electrode 130 and the reflective electrode 150 as described earlier with reference to FIG. 1. Thus a single row driver 18 is provided for both the transmissive and reflective modes, and is operated as described for the embodiment described above with reference to FIG. 4.

FIG. 8 is a schematic diagram showing the arrangement of transmissive pixel/reflective sub-pixels 2 and driving connections in the transflective LCD device of a second embodiment in which the resolution in the reflective mode is one quarter that in the transmissive mode. In this embodiment, the transflective LCD device is the same as that of the embodiment described above with respect to FIGS. 6 and 7, and the same reference numerals are used, in particular with respect to the arrangement of the colours of the reflective colour sub-pixels 6a-6h, and their grouping into reflective pixels and the same reference numerals are used for the same elements, except for the provision of additional TFTs, different row drivers, and different row conductors. More particularly, in this embodiment, as shown in FIG. 8, two TFTs are provided for each transmissive pixel/reflective sub-pixel 2a-2h, with separate TFTs 11 being provided for the transmissive pixels 4a-4h, in addition to the TFTs 10 which in this embodiment are provided for just the reflective sub-pixels 6a-6h i.e. a respective TFT 10 is provided for each reflective sub- pixel 6a-6h by virtue of each respective TFT 10 being electrically connected to a respective reflective electrode 150, and a respective TFT 11 is provided for each transmissive pixel 4a-4h by virtue of each respective TFT 11 being electrically connected to a respective transmissive electrode 130. Furthermore, separate row drivers are provided for driving the TFTs 10 of the reflective sub-pixels 6a-6h compared to the TFTs 11 of the transmissive pixels 4a-4h. These are the same as, and operate the same as, those in the embodiment described earlier with reference to FIG. 5, and the same reference numerals are used in FIG. 8.

In the above embodiments, the transmissive pixels are provided with different colours by being driven in a colour sequential manner. Further embodiments will now be described, with reference to FIGS. 9-15, in which colour sequential driving is not used, and instead each colour transmissive pixel comprises a plurality of differently coloured transmissive sub-pixels, e.g. red, green and blue, as well as each colour reflective pixel comprising a plurality of different coloured reflective sub-pixels, e.g. red, green, blue and white. Different resolution in reflective mode compared to transmissive mode is provided by having more transmissive pixels than reflective pixels.

FIG. 9 is a schematic diagram showing the arrangement of sub-pixels in a first embodiment of a transflective LCD device with differently coloured transmissive sub-pixels. The transflective LCD device has a large number of transmissive and reflective sub-pixels 4 arranged in an array of rows and columns. For clarity, only four reflective sub-pixels 206a-206d and twelve transmissive sub-pixels 203a-203l are shown by way of example. The transmissive sub-pixels 203a-203l and reflective sub-pixels 206a-206b are arranged in rows and columns, such that respective rows of transmissive sub- pixels 203a-203l alternate with respective rows of reflective sub-pixels 206a- 206d. In more detail, reflective sub-pixels 206a and 206b are in a first row, transmissive sub-pixels 203a-203f are in a second row, reflective sub-pixels 206c and 206d are in a third row, and transmissive sub-pixels 203g-203l are in a fourth row. The columnar arrangement of the transmissive sub-pixels is that transmissive sub-pixels 203a and 303g are in a first ("transmissive") column, transmissive sub-pixels 203b and 203h are in a second column, transmissive sub-pixels 203c and 203i are in a third column, transmissive sub-pixels 203d and 203 j are in a fourth column, transmissive sub-pixels 203e and 203k are in a fifth column, and transmissive sub-pixels 203f and 2031 are in a sixth column. In this embodiment each reflective sub-pixel (i.e. one quarter of a reflective pixel) is positionally associated with three transmissive sub-pixels (i.e. one transmissive pixel), more particularly each reflective sub-pixel is positioned so as to be positioned across a row to an extent corresponding to the extent of three transmissive sub-pixels across the next row. Thus, each column of reflective sub-pixels corresponds to three columns of transmissive sub-pixels. In more detail, the reflective sub-pixel 206a and the reflective sub-pixel 206c are in a first ("reflective") column, with reflective sub-pixel 206a positioned above (in the sense of row number) transmissive sub-pixels 203a-203c and with reflective sub-pixel 206c positioned above (in the sense of row number) transmissive sub-pixels 203g-203i; and the reflective sub-pixel 206b and the reflective sub-pixel 206d are in a second ("reflective") column, with reflective sub-pixel 206b positioned above (in the sense of row number) transmissive sub-pixels 203d-203f and with reflective sub-pixel 206d positioned above (in the sense of row number) transmissive sub-pixels 203J-203I. The colours of the sub-pixels are arranged as follows. The reflective sub-pixels 206a-206d are respectively red, green, blue and white, i.e. the reflective sub-pixel 206a is red, the reflective sub-pixel 206b is green, the reflective sub-pixel 206c is blue, and the reflective sub-pixel 206d is white.

The transmissive sub-pixels are arranged in groups of three sub-pixels along a row, each sub-pixel in a group being a respective one of red, green and blue i.e. transmissive sub-pixel 203a is red, transmissive sub-pixel 203b is green, and transmissive sub-pixel 203c is blue; transmissive sub-pixel 203d is red, transmissive sub-pixel 203e is green, and transmissive sub-pixel 203f is blue; transmissive sub-pixel 203g is red, transmissive sub-pixel 203h is green, and transmissive sub-pixel 203i is blue; transmissive sub-pixel 203j is red, transmissive sub-pixel 203k is green, and transmissive sub-pixel 2031 is blue.

The above described colour sub-pixels are grouped to provide colour pixels, as will now be described with reference to FIG. 10. FIG. 10 is a schematic diagram showing the arrangement and layout of four transmissive colour pixels 204a-204d and their associated single reflective colour pixel 212 as provided by the above described sub-pixels in the transflective LCD device of this embodiment. Each transmissive colour pixel 204a-204d comprises one red, one adjacent green and one adjacent blue transmissive sub-pixel from the same row of transmissive sub-pixels, i.e. transmissive colour pixel 204a comprises transmissive sub-pixels 203a (red), 203b (green) and 203c (blue); transmissive colour pixel 204b comprises transmissive sub-pixels 203d (red), 203e (green) and 203f (blue); transmissive colour pixel 204c comprises transmissive sub-pixels 203g (red), 203h (green) and 203i (blue); transmissive colour pixel 204d comprises transmissive sub-pixels 203j (red), 203k (green) and 2031 (blue) (in FIG. 10 the outline of the colour pixels is shown in bold line, whereas the distinction between respective colour sub-pixels is shown in dashed line). The reflective pixel 212 comprises each of the reflective sub- pixels 206a (red), 206b (green), 206c (blue) and 206d (white). This arrangement, in which the four sub-pixels of the reflective pixel 212 are spread over two rows (as opposed to positioning all the four sub-pixels of a given reflective sub-pixel across a single row), again in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user. Also, in this embodiment the resolution in reflective mode is again one quarter that in the transmissive mode, i.e. there are four times as many transmissive pixels as there are reflective pixels, which is again achieved by providing four "colours" of reflective sub-pixel, i.e. red, green, blue and white. As in the above described embodiments where this was the case, this tends to provide the advantage of being particularly convenient to use with common driving software and arrangements, which typically are provided in resolutions which are scaled by a factor of four. Returning to FIG. 9, a respective TFT 210 is located at each reflective sub-pixel 206a-206d and each transmissive sub-pixel 203a-203l.

The overall structure of the transflective LCD device of this embodiment is the same as that described for the above embodiments with reference to FIG. 1 , except that in the present embodiment FIG. 1 shows a cross-section along the line X-Y of FIG. 9, i.e. including two reflective sub-pixels 206b and 206d, with a transmissive sub-pixel 203d therebetween. The items indicated by reference numerals 122, 152, 8, 164 and 4 are essentially as described above, but in this embodiment provide the transmissive sub-pixel 203d. In similar fashion, the two colour filter regions 166 are in this embodiment different colours to each other so that the regions 6 are essentially as described above but in this embodiment provide the two separate reflective sub-pixels 206b and 206d (i.e. unlike in the previous embodiments, where region 4 is a transmissive aperture with a surrounding reflective region 6, here region 4 is a transmissive sub-pixel between two reflective sub-pixels).

Other details of the transflective LCD device, except where otherwise stated in relation to the provision of separate reflective sub-pixels and transmissive sub-pixels, and the driving thereof, again may be as per any conventional transflective LCD device, and are in the present embodiment the same as, and operate the same as, the transflective LCD device disclosed with reference to FIG. 2 of US 6,734,935, the contents of which are contained herein by reference. FIG. 11 is a schematic diagram showing in simplified form the driving connections employed in the transflective LCD device of this embodiment. A column driver 214 is connected to the TFTs 210 via column conductors 216a- 216d, each column conductor 216a-216f being connected to each of the TFTs 210 of a respective column of transmissive sub-pixels 203a-203l. In addition, the TFTs 210 of the reflective sub-pixels 206a-206d are each connected to a different one of the column conductors 216a-216f to which the TFTs 210 of the transmissive sub-pixels 203a-203l are connected. In more detail, the TFT 210 of reflective sub-pixel 206a is connected to column conductor 216a, the TFT 210 of reflective sub-pixel 206c is connected to column conductor 216b, the TFT 210 of reflective sub-pixel 206b is connected to column conductor 216e, and the TFT 210 of reflective sub-pixel 206d is connected to column conductor 216f. In other words the column conductors 216a-216d are used for both the transmissive sub-pixels 203a-203l and the reflective sub-pixels 206a-206d.

Furthermore, note that in this embodiment the TFTs 210 of those reflective sub-pixels in a given column of reflective sub-pixels (e.g. red reflective sub-pixel 206a and blue reflective sub-pixel 206c) are connected to different column conductors (here column conductors 216a and 216b respectively). This arrangement may conveniently be referred to as "staggered". Separate row drivers are provided for driving the TFTs 210 of the reflective sub-pixels 206a-206d compared to the TFTs 210 of the transmissive sub-pixels 203a-203l. In more detail, a reflective mode row driver 222 is connected to the TFTS 10 of the reflective sub-pixels 206a-206d via reflective mode row conductors 224a and 224b, and a separate transmissive mode row driver 226 is connected to the transmissive sub-pixels 203a-203l via separate transmissive mode row conductors 228a and 228b. In operation, the row drivers 222 and 226 select one row of sub-pixels at a time, and the column driver 214 provides data signal levels to the columns in synchronisation therewith. The use of separate row drivers 222 and 226 for the reflective mode and transmissive mode respectively allows the transmissive pixels to be driven with different data compared to the reflective sub-pixels, i.e. provide separate images which may be adapted to suit the respective differing resolutions.

In this embodiment the resolution of the transmissive mode is four times that of the reflective mode. This is surprisingly beneficial, inter alia because of the realisation by the present inventor that such improved resolution is primarily desired in the transmissive mode as opposed to in the reflective mode. Moreover, an additional advantage compared to the embodiments described above with respect to FIGS. 2-8 is that the need to provide an aperture for the transmissive pixel within a surrounding reflective sub-pixel area is removed. This further allows improvements in achievable resolution, as the effect of manufacturing tolerances tends to be alleviated. This allows, in combination with the use of lower reflective resolution, a particularly advantageous possibility for overall improved resolution in the transmissive mode. The same types of benefit can be achieved with other driving/connection arrangements and or sub-pixel layouts, for example those which will now be described with reference to FIGS. 12-15. FIG. 12 is a schematic diagram showing in simplified form the driving connections employed in a transflective LCD device of a further embodiment. In this embodiment, the transflective LCD device, including column driver 214 and column conductors 216a-216f, is the same as that in the embodiment described above with reference to FIGS. 9-11 , except for differences in the provision of TFTs, row driver and row conductors, as will now be explained in more detail. In this embodiment, as shown in FIG. 12, there are no separate TFTs 10 provided for the reflective sub-pixels 206a-206d, and instead the some of the TFTs 10 provided for the transmissive sub-pixels 203a-203l are also used for switching the reflective sub-pixels 206a-206d. In particular, referring to FIG. 12 where the shared TFTs 210 are indicated by asterisks (*) for convenience, in this embodiment, the TFT 210 of transmissive sub-pixel 203a is shared by reflective sub-pixel 206a, the TFT 210 of transmissive sub- pixel 203e is shared by reflective sub-pixel 206b, the TFT 210 of transmissive sub-pixel 203h is shared by reflective sub-pixel 206c, and the TFT 210 of transmissive sub-pixel 203I is shared by reflective sub-pixel 206d. Thus in this embodiment the TFTs 210 of those reflective sub-pixels in a given column of reflective sub-pixels (e.g. red reflective sub-pixel 206a and blue reflective sub- pixel 206c) are again connected to different column conductors (here again column conductors 216a and 216b respectively), i.e. the arrangement is again "staggered", with the same benefits as for the embodiment described above with reference to FIGS. 9-11. Also, instead of a separate row driver for the reflective sub-pixels 206a-

206d and the transmissive sub-pixels 203a-203l, a common row driver 218 for both reflective and transmissive sub-pixels is provided. The row driver 218 is connected to the TFTS 210 via row conductors 220a and 220b, each connected to each of the TFTs 10 of a respective row of transmissive sub- pixels 203a and reflective sub-pixels 206a-206d sharing the particular TFTs 10.

In operation, the row driver 218 selects one "combined" row of reflective sub-pixels 206a-206d and transmissive sub-pixels 203a-203l at a time, and the column driver provides data signal levels to the columns in synchronisation therewith. Thus in this embodiment, as with the embodiment described earlier with reference to FIG. 4, the row driver 218 carries out the row selection driving for both the transmissive mode and the reflective mode of operation such that the transmissive pixels and reflective sub-pixels are driven with the same data as each other, i.e. provide corresponding images but of different resolution.

FIG. 13 is a schematic diagram showing in simplified form the driving connections employed in a transflective LCD device of a further embodiment. In this embodiment, the transflective LCD device, including column driver 214, column conductors 216a-216f, reflective mode row driver 222, reflective mode row conductors 224a and 224b, transmissive mode row driver 226 and transmissive mode row conductors 228a, is the same as that in the embodiment described above with reference to FIGS. 9-11 , except additional TFTs are provided, as will now be explained in more detail. In this embodiment, as shown in FIG. 13, three TFTs 210 are provided for each reflective sub-pixel 206a-206d. As described above, each reflective sub-pixel 206a-206d is positioned above (in the sense of row number) the three differently coloured transmissive sub-pixels of a transmissive pixel, with each of the three differently coloured transmissive sub-pixels being connected to respective adjacent column conductors. In this embodiment, each of the three TFTs 210 of a given reflective sub-pixel 206a-206d is connected to a respective one of these adjacent column conductors. For example, a first TFT 210 of the red reflective sub-pixel 206a and a first TFT 210 of the blue reflective sub-pixel 206c are both connected to the column conductor 216a that is connected to the TFTs 210 of the red transmissive sub-pixels 203a and 203g, a second TFT 210 of the red reflective sub-pixel 206a and a second TFT 210 of the blue reflective sub-pixel 206c are both connected to the column conductor 216b that is connected to the TFTs 210 of the green transmissive sub-pixels 203b and 203h, and a third TFT 210 of the red reflective sub-pixel 206a and a third TFT 210 of the blue reflective sub-pixel 206c are both connected to the column conductor 216c that is connected to the TFTs 210 of the blue transmissive sub-pixels 203c and 203i. Again, in operation, the row drivers 222 and 226 select one row of sub- pixels at a time, and the column driver 214 provides data signal levels to the columns in synchronisation therewith. The use of separate row drivers 222 and 226 for the reflective mode and transmissive mode respectively allows the transmissive pixels to be driven with different data compared to the reflective sub-pixels, i.e. provide separate images which may be adapted to suit the respective differing resolutions. It will be appreciated that many other embodiments are possible in which the sub-pixels may be arranged in layouts other than those of the embodiment described above.

FIG. 14 is a schematic diagram showing the arrangement and layout of sub-pixels and pixels of one set of such further embodiments. In these embodiments each reflective pixel again comprises four differently coloured reflective sub-pixels, i.e. red, green, blue and white, and each transmissive colour pixel again comprises three differently coloured sub-pixels, i.e. red, green and blue. Again, one reflective sub-pixel is provided for every four transmissive pixels. The transflective LCD device of these embodiments are therefore the same as those of the embodiments described above with reference to FIGS. 9-13, except for the layout of the sub-pixels which is as shown in FIG. 14. In particular the various ways in which the TFTs and row drivers and conductors may be provided are the same as in the earlier embodiments, or are readily adapted by the skilled person in view of the description of the earlier embodiments, and hence for convenience these are not shown again in, or described again with reference to, FIG. 14.

In FIG. 14, only four reflective sub-pixels 206a-206d and twelve transmissive sub-pixels 203a-203l are again shown by way of example. The transmissive sub-pixels 203a-203l and reflective sub-pixels 206a-206d are arranged in rows and columns, such that each row comprises transmissive sub-pixels and reflective sub-pixels. In more detail, in one row, individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203a, then green transmissive sub-pixel 203b, then blue transmissive sub-pixel 203c) are positioned adjacently along the row, followed by a red reflective sub-pixel (the red reflective sub-pixel 206a), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203d, then green transmissive sub-pixel 203e, then blue transmissive sub-pixel 203f) positioned adjacently along the row, followed by a green reflective sub-pixel (the green reflective sub-pixel 206b). This arrangement of red and green reflective sub- pixels being interspersed amongst groups of the three colours of transmissive sub-pixels is continued across the row (not shown).

Similarly, in the next row, individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203g, then green transmissive sub-pixel 203h, then blue transmissive sub-pixel 203i) are positioned adjacently along the row, followed by a blue reflective sub-pixel (the blue reflective sub-pixel 206c), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203j, then green transmissive sub-pixel 203k, then blue transmissive sub-pixel 2031) positioned adjacently along the row, followed by a white reflective sub-pixel (the white reflective sub-pixel 206d). This arrangement of blue and white reflective sub-pixels being interspersed amongst groups of the three colours of transmissive sub-pixels is continued across the row (not shown). Furthermore, this arrangement of alternating between rows having red and green interspersed reflective sub-pixels or blue and white interspersed reflective sub-pixels is continued down the rows of the array (not shown).

The colour sub-pixels are grouped to provide colour pixels, as follows. Each of the above described groups of three adjacently positioned individual transmissive sub-pixels of each of the three colours red, green and blue provide a respective transmissive pixel. In more detail, the red transmissive sub-pixel 203a, the green transmissive sub-pixel 203b and the blue transmissive sub-pixel 203c together form a first transmissive pixel 204a; the red transmissive sub-pixel 203d, the green transmissive sub-pixel 203e and the blue transmissive sub-pixel 203f together form a second transmissive pixel 204b; the red transmissive sub-pixel 203g, the green transmissive sub-pixel 203h and the blue transmissive sub-pixel 203i together form a third transmissive pixel 204c; and the red transmissive sub-pixel 203j, the green transmissive sub-pixel 203k and the blue transmissive sub-pixel 2031 together form a fourth transmissive pixel 204d (in FIG. 10 the outline of the colour pixels is shown in bold line, whereas the distinction between respective colour sub- pixels is shown in dashed line). The reflective pixel 212 comprises each of the reflective sub-pixels 206a (red), 206b (green), 206c (blue) and 206d (white). This arrangement, in which the four sub-pixels of the reflective pixel 212 are spread over two rows (as opposed to positioning all the four sub-pixels of a given reflective sub-pixel across a single row), again in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user. Also, in this embodiment the resolution in reflective mode is again one quarter that in the transmissive mode, i.e. there are four times as many transmissive pixels 204a-204d as there are reflective pixels 212. FIG. 15 is a schematic diagram showing the arrangement and layout of sub-pixels and pixels in another set of embodiments. In these embodiments each reflective pixel comprises three differently coloured reflective sub-pixels, i.e. red, green and blue, and each transmissive colour pixel also comprises three differently coloured sub-pixels, i.e. red, green and blue. In these embodiments one reflective sub-pixel is provided for every three transmissive pixels. Except for these details and the layout of the sub-pixels, the transflective LCD device of these embodiments are the same as those of the embodiments described above with reference to FIG. 14. Furthermore, as with the embodiments described above with reference to FIG. 14, the various ways in which the TFTs and row drivers and conductors may be provided are the same as in earlier embodiments, or are readily adapted by the skilled person in view of the description of the earlier embodiments, and hence for convenience these are not shown again in, or described again with reference to, FIG. 15.

In FIG. 15, only six reflective sub-pixels 206a-206f and eighteen transmissive sub-pixels 203a-203r are shown by way of example. The transmissive sub-pixels 203a-203r and reflective sub-pixels 206a-206f are arranged in rows and columns, such that each row comprises transmissive sub-pixels and reflective sub-pixels. In more detail, in one row, individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203a, then green transmissive sub-pixel 203b, then blue transmissive sub-pixel 203c) are positioned adjacently along the row, followed by a red reflective sub-pixel (the red reflective sub-pixel 206a), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203d, then green transmissive sub-pixel 203e, then blue transmissive sub-pixel 203f) positioned adjacently along the row, followed by a green reflective sub-pixel (the green reflective sub-pixel 206b), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub- pixel 203m, then green transmissive sub-pixel 203n, then blue transmissive sub-pixel 203o) positioned adjacently along the row, followed by a blue reflective sub-pixel (the blue reflective sub-pixel 206e). This arrangement of red, green and blue reflective sub-pixels being interspersed in this order amongst groups of the three colours of transmissive sub-pixels is continued across the row (not shown).

Similarly, in the next row, individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203g, then green transmissive sub-pixel 203h, then blue transmissive sub-pixel 203i) are positioned adjacently along the row, followed by a blue reflective sub-pixel (the blue reflective sub-pixel 206c), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203j, then green transmissive sub-pixel 203k, then blue transmissive sub-pixel 2031) positioned adjacently along the row, followed by a red reflective sub-pixel (the red reflective sub-pixel 206d), followed by further individual transmissive sub-pixels of each of the three colours of transmissive sub-pixel (red transmissive sub-pixel 203p, then green transmissive sub-pixel 203q, then blue transmissive sub-pixel 203r) positioned adjacently along the row, followed by a green reflective sub-pixel (the green reflective sub-pixel 206f). This arrangement of blue, red and green reflective sub-pixels being interspersed amongst groups of the three colours of transmissive sub-pixels, with the colours offset to those of the previous row, is continued across the row (not shown). Furthermore, this arrangement of each row having rows having red, green and blue interspersed reflective sub-pixels, but with the colours offset in consecutive rows, is continued down the rows of the array (not shown). The colour sub-pixels are grouped to provide colour pixels, in a so- called delta/nablet layout, as follows. Each of the above described groups of three adjacently positioned individual transmissive sub-pixels of each of the three colours red, green and blue provide a respective transmissive pixel. In more detail, the red transmissive sub-pixel 203a, the green transmissive sub- pixel 203b and the blue transmissive sub-pixel 203c together form a first transmissive pixel 204a; the red transmissive sub-pixel 203d, the green transmissive sub-pixel 203e and the blue transmissive sub-pixel 203f together form a second transmissive pixel 204b; the red transmissive sub-pixel 203g, the green transmissive sub-pixel 203h and the blue transmissive sub-pixel 203i together form a third transmissive pixel 204c; the red transmissive sub-pixel 203j, the green transmissive sub-pixel 203k and the blue transmissive sub- pixel 2031 together form a fourth transmissive pixel 204d; the red transmissive sub-pixel 203m, the green transmissive sub-pixel 203n and the blue transmissive sub-pixel 203o together form a fifth transmissive pixel 204e; and the red transmissive sub-pixel 203p, the green transmissive sub-pixel 203q and the blue transmissive sub-pixel 203r together form a sixth transmissive pixel 204f (in FIG. 10 the outline of the colour pixels is shown in bold line, whereas the distinction between respective colour sub-pixels is shown in dashed line).

Each of the two reflective colour pixels 212a and 212b comprises one red, one green and one blue reflective colour sub-pixel of the above described sub-pixels 206a-206f. In each pixel, two sub-pixels are from a given row and the third sub-pixel is from an adjoining row. In more detail, the first reflective colour pixel 212a comprises the first and second reflective sub-pixels of the first row, i.e. the red reflective sub-pixel 206a and the green reflective sub-pixel 206b, and the first reflective sub-pixel of the second row, i.e. the blue reflective sub-pixel 206c. The second reflective colour pixel 212b comprises the second and third reflective sub-pixels of the second row, i.e. the red reflective sub- pixel 206d and the green reflective sub-pixel 206f, and the third reflective sub- pixel of the first row, i.e. the blue reflective sub-pixel 206e. It can be seen that these two pixels 12a and 12b form an interlocking pattern. This pattern is repeated throughout the array,

This arrangement, in which the three sub-pixels of each reflective pixel 212a and 212b are spread over two rows (as opposed to positioning all the three sub-pixels of a given reflective sub-pixel across a single row), again in effect "shares" the lower resolution of the reflective mode between the vertical and the horizontal resolutions, thereby tending to improve the perception of the image to a user. Furthermore, in this embodiment the resolution in reflective mode is one third that in the transmissive mode, i.e. there are three times as many transmissive pixels 204a-204f as there are reflective pixels 212a and 212b.

The above embodiments comprise certain examples of pixel and sub- pixel layout or arrangement, including allocation of colours. It will be appreciated that in other embodiments, other arrangements are possible. For example, different colours other than red, green and blue or red, green, blue and white may be employed. Also, other sub-pixel/pixel relationships may be employed, e.g. there may be more than one sub-pixel of a given colour in a pixel. Also, the sub-pixels may be grouped into pixels in other ways, for example a delta/nablet layout may be employed instead of that shown in FIG. 3, and so on.

In the FIGS, the areas of the various sub-pixels are not drawn to scale, The areas may be the same for different colour sub-pixels and where appropriate for reflective and transmissive sub-pixels, but on the other hand they may be different in other embodiments. In the above described embodiments the reflective sub-pixels of a given pixel are arranged over at least two rows, such that in effect the lower resolution of the reflective mode is "shared" between the vertical and the horizontal resolutions. However this need not be the case, and in other embodiments all the sub-pixels of a given reflective sub-pixel may be in the same row as each other.

In the above described embodiments certain specific driving arrangements, provided by TFTs, row and column drivers, and row and column conductors, are employed. However, these may be varied as required by the skilled person, and as such in other embodiments other driving arrangements may be employed.

In the above embodiments, the differing resolution is with transmissive mode having greater resolution than reflective resolution. However, in other embodiments, where resolution in reflective mode is particularly of interest, the differing resolution is implemented as the reflective mode having greater resolution than the transmissive mode. This is implemented by providing more reflective pixels than transmissive pixels, e.g. "swapping" the reflective sub- pixels and the transmissive sub-pixels in the embodiments described with reference to FIGS. 9-15.

Claims

1. A transflective display device, comprising: an array of transmissive pixels (4a-4l; 204a-204d) and reflective pixels (12a-12d; 212); wherein the array comprises a different number of transmissive pixels (4a-4l; 204a-204d) compared to reflective pixels (12a-12d; 212) arranged such that the resolution of an image displayed in transmissive mode is different to the resolution of a corresponding image displayed in reflective mode.

2. A device according to claim 1 , wherein the array comprises more transmissive pixels (4a-4l; 204a-204d) than reflective pixels (12a-12d; 212) such that the resolution of an image displayed in transmissive mode is greater than the resolution of a corresponding image displayed in reflective mode.

3. A device according to claim 2, wherein there are four times as many transmissive pixels as there are reflective pixels.

4. A device according to claim 2, wherein each reflective pixel (12a- 12d; 212) comprises a plurality of differently coloured reflective sub-pixels (6a-

6I; 206a-206d), and each colour reflective sub-pixel (6a-6l; 206a-206d) of a reflective pixel (12a-12d; 212) is associated with a respective transmissive pixel (4a-4l; 204a-204d).

5. A device according to claim 4, wherein each reflective pixel

(12a-12d; 212) comprises a red reflective sub-pixel, a green reflective sub- pixel, a blue reflective sub-pixel and a white reflective sub-pixel.

6. A device according to any of claims 1 to 5, wherein reflective sub-pixels (6a-6l; 206a-206d) of a given reflective pixel (12a-12d; 212) are arranged over at least two rows and two columns of the array.

7. A device according to any of claims 1 to 6, wherein separate thin film transistors (10, 11) are provided for the reflective pixels (12a-12d; 212) and the transmissive pixels (4a-4l; 204a-204d).

8. A device according to any of claims 1 to 6, wherein thin film transistors (10) are shared between the reflective pixels (12a-12d; 212) and the transmissive pixels (4a-4l; 204a-204d).

9. A device according to any of claims 1 to 8, wherein each transmissive pixel (4a-4l) comprises a transmissive aperture (8) surrounded by a coloured reflective sub-pixel (6a-6l); and the device further comprises means for displaying different colours to the transmissive pixel (4a-4l) by colour sequential driving.

10. A device according to any of claims 1 to 8, wherein each transmissive pixel (204a-204d) comprises a plurality of differently coloured transmissive sub-pixels (203a-203l).

11. A device according to claim 10, wherein the array comprises differently coloured transmissive sub-pixels (203a-203l) arranged adjacently along rows to provide transmissive pixels (204a-204d), and differently coloured reflective sub pixels (206a-206d) interspersed, along the rows, between the transmissive pixels (204a-204d).

12. A device according to claim 10, wherein rows of transmissive sub-pixels (203a-203l) alternate with rows of reflective sub-pixels (206a-206d).