JPS60260922A - Display lighting device for liquid crystal element - Google Patents

Abstract

PURPOSE:To perform illumination suitable for the characteristic of a liquid crystal element and having good efficiency, by irradiating the lighting lights of a scanning drive type display lighting device only upon the picture element of gate lines, whose time elapsed after writing is completed is within a fixed value. CONSTITUTION:A liquid crystal element 21 is driven in accordance with the characteristic of TV pictures received through an antenna 10 and video signals Va are inputted in a control block 16 through a synchronizing separation circuit 14. A scan side driving circuit 20 successively supplies select signals to each gate line of the display element 21 in accordance with the prescribed timing control signal of the output of the control block 16 and a signal side driving circuit 19 supplies drive signals to display luminance. On the other hand, a vertical and horizontal deflecting circuits 23 and 24 give a CRT22 behind the element 21 saw tooth wave signals Sv and Sh for vertical and horizontal deflection upon receiving vertical and horizontal scanning control signals Tv and Th from the block 16. Since the signal Tv is delayed from a vertical synchronizing signal from the circuit 14 by a prescribed time, efficient illumination can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a display illumination device for a liquid crystal display element, in which switch elements are arranged in a matrix on one substrate constituting a display cell.

[Technical background]

In recent years, with the development of electronic circuit technology and electro-optical display technology, portable liquid crystal televisions configured to display television images using liquid crystal display elements have also been realized.

Furthermore, as a display element for the above-mentioned liquid crystal television, so-called TF (TF) is used, in which switch elements made of thin film transistors are arranged in a matrix on the surface of a transparent substrate such as a glass.
A T (Thin Film Transistor) type active matrix liquid crystal display element is known as the most suitable one.

FIG. 6 is a circuit diagram showing the structure of a general TFT type active matrix liquid crystal display element, and FIG. 7 is an enlarged view showing a part of the structure as a model.

The liquid crystal display element shown in FIG.
m scanning side lines (gate lines) consisting of y1~
It has n signal side lines (data lines) consisting of yn, forming m×n picture elements. A thin film MOS transistor 1 is formed as a switch element corresponding to each picture element, and an equivalent liquid crystal resistor R and capacitor C are connected to each thin film MOS transistor 1.

In FIG. 7, X corresponds to a gate line and yJ corresponds to a data line, and the drain side electrode of each transistor 1 is connected to the electrode 2 of each picture element of the liquid crystal display element.

The active matrix liquid crystal display element as mentioned above is
The gate lines are sequentially selected and the transistors are turned on, and the display content is written by supplying a display drive signal corresponding to the brightness of each picture element of the selected gate line from the data line. Furthermore, for the gate lines that have returned to the non-selected state after completing the writing, the transistors are turned off.
It is driven in such a manner that the gate line is controlled to be in the FF state and the written display content is held until the gate line becomes selected again after field (1).

In other words, in an active matrix liquid crystal display element, the display content is written to each cell picture element at a cycle of each field, and the display content is retained until the next field, so the display quality is low. As is well known, it is not very susceptible to the influence of so-called crosstalk or the selection duty ratio on the scanning line side.

However, even with the above-mentioned TFT active matrix liquid crystal display element, there still remains the drawback that the display is very dark, as with other types of liquid crystal display elements, and so-called color stripe filters, etc. In the color liquid crystal display element used, in particular, the amount of light transmitted is extremely small, so it was necessary to illuminate the display section with strong illumination light. Therefore, it is clear that securing strong display illumination light and improving the energy efficiency of illumination pose serious problems, especially in portable color liquid crystal televisions.

In addition, in TFT-type active matrix liquid crystal display elements, although it is said that the selection duty on the scanning line side is not affected much, the initial state of writing is not completely retained for the period of one field. , actually decays at a considerable speed, so that the displayed content of the picture element on the Kate line immediately before the next writing is considerably degraded.

For example, assuming that the number of gate lines is about 200, the TV image is 60 fields (30 frames) per second, so the time width that one gate line is in the selected state is 60 μs, and the field period is 16 ms. Therefore, ideally, for each picture element, it is necessary to complete writing within 60 μs and retain the written display content over a period of 16 ms.

On the other hand, the size of each picture element is
(size) is about 200 x 200 μm2, the values of the equivalent resistance R and capacitance C of the liquid crystal connected to each thin film MOS transistor 1 are R=1010Ω,
Since C=5×10 −13 F, the time constant of the liquid crystal alone is only about 5 ms. Furthermore, if the ratio between the ON resistance and the OFF resistance of each thin film MOS transistor 1 is not sufficient, the attenuation after writing will become even faster.

Taking the above into consideration, when illuminating a display using an active matrix liquid crystal display element as described above, it is possible to illuminate the picture elements of the line immediately after writing, and also after the pixels have attenuated after a relatively long time has elapsed since writing. It is clear that it is not preferable in terms of energy efficiency to irradiate the picture elements of the line indiscriminately or uniformly with powerful illumination light that requires a large amount of power.

[Object of the Invention] An object of the present invention is to provide a display illumination device for a liquid crystal display element in which switch elements are arranged in a matrix on one substrate constituting a display cell, with illumination efficiency adapted to the characteristics of the liquid crystal display element. The object of the present invention is to realize a good display lighting device.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show a liquid crystal television equipped with a display lighting device according to an embodiment of the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof.

In FIG. 1, 10 is an antenna for receiving television broadcast waves, 11 is a part of a tuner consisting of a high frequency amplifier, a mixer, a local oscillator, etc., 12 is an intermediate frequency amplifier, and 13 is a video detection/amplifier, which are well known as above. It constitutes the television signal receiving section of the.

The synchronization separation circuit 14 receives the video signal Va supplied from the video detection/amplifier 13, performs synchronization separation, and outputs horizontal and vertical synchronization signals, and the A/D conversion circuit 15 generates analog signals. The video signal Va is converted into a display signal Vcl consisting of a digital signal corresponding to the luminance level.

The control block 16 generates timing control signals Td necessary for driving the TFT active matrix liquid crystal display element 21 and a CRT 22 for display illumination, which will be described later, based on the synchronization signals from the synchronization separation circuit 14. Each scanning timing control signal Th, Tv, etc. for driving is formed.

The display signal Vd serially outputted from the A/D conversion circuit 15 is sent to a serial/parallel conversion circuit 17 consisting of a shift register.
The signals are sequentially input to the control block 16, converted into parallel signals, and further latched into the line memory 18 in accordance with a predetermined timing control signal from the control block 16. That is, the line memory 18 is configured so that display signals for one new scanning line are sequentially latched at each scanning shift timing of the liquid crystal display element 21.

On the other hand, the scanning side drive circuit 20 sequentially supplies a selection signal to each gate line of the liquid crystal display element 21 according to a predetermined timing control signal from the control block 16, and the signal side drive circuit 19 supplies a selection signal to each gate line of the liquid crystal display element 21 in accordance with a predetermined timing control signal from the control block 16. Based on the output signal of 8, a drive signal corresponding to the display brightness is supplied to the source side of each transistor of the gate line in the selected state.

Further, on the back side of the liquid crystal display element 21 of this embodiment, there is a flat CRT 22 which is a raster scanning type self-luminous element.
is installed as a display lighting device. The control block 16 described above forms vertical and horizontal scanning timing control signals Tv and Th in response to vertical and horizontal synchronization signals from the synchronization separation circuit 14, and also generates vertical and horizontal scanning timing control signals Tv and Th, respectively. The horizontal deflection circuit 24 generates a ground wave signal sv for vertical deflection control and a ground wave signal sv for horizontal deflection control based on the vertical and horizontal scanning timing control signals Tv and Th from the control block 16, respectively. A truncated wave signal S is formed and supplied to the CRT 22. The vertical scanning timing control signal TV basically has the characteristics of a timing signal obtained by delaying the vertical synchronization signal from the synchronization separation circuit 14 by a predetermined time width.

Next, FIG. 2 is a sectional view showing the structure of the display section, in which a liquid crystal display element 2 consisting of an upper substrate 21a, a lower substrate 21b, etc.
A so-called flat type CRT 22 is disposed on the back side of the device 1 . That is, the lower substrate 21 of the liquid crystal display element 21
a and 21b are made of transparent glass substrates, and CRT22
The illumination light from passes through the liquid crystal display element 21. Note 25
2 is a cover member, and 26 is a printed circuit board. Further, a thin film transistor is formed as a switch element on the inner surface side of the lower substrate 21b of the liquid crystal display element 21, and a CRT 22
A fluorescent screen 22a is formed on the upper inner surface.

Further, FIG. 3 is an explanatory diagram of the display illumination operation in this embodiment, and FIG. 4 is a time chart diagram schematically showing the scanning timing of the CRT 22 in the vertical direction.

The operation of the display lighting device of this embodiment will be described below.

Since the liquid crystal display element 21 is driven according to the characteristics of the television image, each scanning side line (category line) of X1 to X□
For each field of the video signal Va, one cycle of scanning is performed. Note that ×1 to ×1 in FIG. 4 indicate that the liquid crystal display element 2 is
1 shows selection signals applied to each of the gate lines x1 to xm of No. 1. (In this embodiment, the switch transistor of each picture element is an N-channel type.) Also, the period T is equal to one field (one vertical period) for both the video signal Va and the scanning side drive signal of the liquid crystal display element 21. T1 corresponds to the selection duty (one horizontal period) on the gate line side of the liquid crystal display element 21.

Therefore, for each field, by first selecting the first gate line X with the pulse XI, when the display writing drive to the n picture elements belonging to the first gate VAX is completed, the next The second gate line x2 is selected by the pulse X2, the third gate line X is selected by the pulse X3, and so on, and finally the m-th gate line is selected by the pulse x1. When the display writing drive for X is completed, 1
After completing the scanning cycle, the next field can be scanned. However, as mentioned above, the display state of the picture element belonging to each gate line attenuates over time from immediately after being driven for display writing until the next scanning timing is reached and it is once again driven for display writing. I will do it.

Here, in this embodiment, for each field, writing drive is first started for the first gate line X, but after a predetermined time elapses, raster scanning of the CRT 22 is started. It is composed of

That is, when the writing drive of each pixel of the first gate line , horizontal scanning 1 in the CRT 22 is performed, illumination light is irradiated to the first row position, and then, when the writing drive for the second gate line x2 is completed, immediately after that, the second gate line Corresponding to the second row position, the second horizontal scanning illumination is performed. Immediately after the writing drive ends, the pixels of each gate line are always illuminated by the scanning of the CRT 22. It is configured to provide illumination light.

Although the sawtooth wave signal S for horizontal deflection control is omitted in FIG. 4, the sawtooth wave signal Sv for vertical deflection control is applied to the first gate line X in each field as shown in the figure. The m-th gate line X from time t after the selection signal X1. The selection signal X□ continues to rise until time t has elapsed.
Compared to the scanning timing of CRT2
The scanning timing in the vertical direction of 2 is delayed in phase by a time width of .

As a result, in this embodiment, the picture elements belonging to each Kate line of the liquid crystal display element 21 are displayed immediately after the display writing ends (time t after the start of writing), but before the display state attenuates. It will receive scanning illumination from the CRT 22.

Note that in FIG. 4, 1v corresponds to the vertical blanking period of the CRT 22. Regarding the sawtooth wave signal sh for horizontal deflection control, one period (one horizontal period) of horizontal scanning of the CRT 22 does not necessarily correspond to the period of the horizontal scanning of the liquid crystal display element 2.
It is not necessary to configure the selection duty (one horizontal period) T1 on the gate line side of 1; for example, the period of the sawtooth wave signal Sh for horizontal deflection control can be set to
By making it sufficiently smaller than the gate line side selection period T1 of 1, it is also possible to perform scanning irradiation with illumination light more precisely on the picture elements of each row.

Furthermore, regarding the sawtooth signal sv for vertical deflection control,
It is only necessary that the timing of each vertical scanning of the CRT 22 is synchronized with the drive timing of each field of the liquid crystal display element 21 so that it is delayed or more than a certain time width overall. , for example, when the period of the sawtooth wave signal S for horizontal deflection control is sufficiently small compared to the gate line side selection period T1 of the liquid crystal display element 21, the vertical deflection of the waveform shown in FIG. The vertical deflection of the CRT 22 may be controlled by the control sawtooth signal Sv.

However, if the above delay time width t becomes too large, the illumination light will be irradiated to that part after the display state has considerably attenuated. In order to perform light irradiation, it is better to make it as small as possible within the range of the pulse width t1 or more of the gate line selection signal (if it is less than t1, illumination light irradiation will be performed before the end of writing). However, it is preferable that the maximum period be less than half of one field period T (that is, t1≦t≦T/2).

〔Effect of the invention〕

As described above, according to the present invention, instead of irradiating illumination light indiscriminately to pixels belonging to all gate lines, pixels of gate lines whose elapsed time after completion of writing is within a certain value. Since the illumination light of the scanning drive type display illumination device is applied only to the illumination area, very energy efficient display illumination can be realized. In other words, in portable LCD TVs that use color LCD display elements, the display tends to be particularly dark.
Since strong display illumination light is required and batteries are the energy source for driving, it is necessary to improve the energy efficiency of display illumination and save as much power as possible for illumination. The intense illumination light from the molded lighting device is always directed preferentially to areas with high lighting efficiency, making it possible to bring out the maximum display lighting effect with the minimum amount of power. .

Note that scanning drive type illumination equipment does not necessarily require CR.
It is clear that the present invention can be applied to the present invention as long as it is of a type that is scanned and driven at least in the vertical direction; for example, an EL (electroluminescence) that is divided into a plurality of blocks in the vertical direction. The illumination panel may be configured to sequentially scan and drive from the upper block to the lower block.

Further, the display lighting device can also be configured to be detachable from the liquid crystal display element.

[Brief explanation of the drawing]

1 to 4 show a display lighting device for a liquid crystal television according to an embodiment of the present invention, FIG. 1 is a block diagram showing the overall configuration thereof, and FIG. 2 shows the structure of the display section. FIG. 3 is a cross-sectional view, FIG. 3 is an explanatory diagram of display illumination operation, and FIG. 4 is a time chart diagram schematically showing scanning timing in the vertical direction of a CRT for display illumination. FIG. 5 is a time chart diagram showing another embodiment. Figure 6 shows a typical TFT
FIG. 7 is an enlarged view showing a part of the structure as a model. 16...Control block, 2l...
TFT type active matrix liquid crystal display element, 22.
... Flat type CRT, 23 ... Vertical deflection circuit, 24
...Horizontal deflection circuit, Va...Video signal,
Tv...Vertical scanning timing control signal, Th...Horizontal scanning timing control signal, Sv...Sawtooth wave signal for vertical deflection control,
Sv: Sawtooth wave signal for horizontal deflection control. Patent applicant Citizen Watch Co., Ltd. Figure 2 21 N2 3 N 1 Figure 4 1 Figure 5rXJ Figure 6

Claims (2)

[Claims] (1) In a display illumination device for a liquid crystal display element in which switch elements are arranged in a matrix on one substrate constituting a display cell, a display illumination device is provided on the back side of the liquid crystal display element so as to be scanned at least in the vertical direction. The scanning drive type illumination device is configured to perform scanning in the vertical direction at a timing synchronized with the scanning timing of the liquid crystal display element so as to be delayed by a predetermined time width. 1. A display illumination device for a liquid crystal display element, comprising a control signal forming means for forming a scanning timing control signal for scanning and timing control. (2) The scanning drive type display lighting device is a flat CRT.
and the control signal forming means is composed of the flat type CR.
The liquid crystal display element according to claim 1, wherein the liquid crystal display element is configured to supply a scanning timing control signal to each of a horizontal deflection circuit and a vertical deflection circuit for raster scanning T. display lighting equipment.