LIQUID CRYSTAL DISPLAY SYSTEMS AND RELATED METHODS WITH PIXEL ELEMENTS DRIVEN AT DIFFERENT FREQUENCIES

Abstract

Liquid crystal display (LCD) systems and related methods with pixel elements driven at different frequencies are provided. A representative LCD system includes: a plurality of pixel elements arranged in an array, each of the plurality of pixel elements having a first sub-region and a second sub-region; a low-frequency driving circuit operative to drive each of the first sub-regions; and a high-frequency driving circuit operative to drive each of the second sub-regions at a driving frequency different than a driving frequency of the low-frequency driving circuits; wherein the first sub-regions exhibit a different size than the second sub-regions.

Claims

1. A liquid crystal display (LCD) system comprising: a plurality of pixel elements arranged in an array, each of the plurality of pixel elements having a first sub-region and a second sub-region; a low-frequency driving circuit operative to drive each of the first sub-regions; and a high-frequency driving circuit operative to drive each of the second sub-regions at a driving frequency different than a driving frequency of the low-frequency driving circuits; wherein the first sub-regions exhibit a different size than the second sub-regions.

2. The LCD system of claim 1, wherein the first sub-regions are smaller than the second sub-regions.

3. The LCD system of claim 1, wherein the driving frequency of the high-frequency driving circuits is a multiple of the driving frequency of the low-frequency driving circuits.

4. The LCD system of claim 1, wherein: the plurality of pixel elements have a plurality of first electrodes associated with the first sub-regions and a plurality of second electrodes associated with the second sub-regions; and the plurality of first electrodes exhibit a different configuration than the plurality of second electrodes.

5. The LCD system of claim 4, wherein the first electrodes exhibit gaps between adjacent ones of the first electrodes that are narrower than gaps exhibited between adjacent ones of the second electrodes.

6. The LCD system of claim 4, further comprising: a first substrate; a second substrate; and a liquid crystal material disposed between the first substrate and the second substrate; wherein the first electrodes and the second electrodes are located on the first substrate.

7. The LCD system of claim 1, wherein a ratio of the size of the first sub-region and the second sub-region is in the range of 1 to approximately 10, but 1 is excluded.

8. The LCD system of claim 1, wherein each of the second sub-regions is at least two times larger or smaller than each of the first sub-regions.

9. The LCD system of claim 1, wherein the plurality of pixel elements comprises blue phase liquid crystal.

10. The LCD system of claim 1, further comprising: a first data line communicating with each of the low-frequency driving circuits; a second data line communicating with each of the high-frequency driving circuits; a first gate line communicating with each of the low-frequency driving circuits; and a second gate line communicating with each of the high-frequency driving circuits.

11. The LCD system of claim 10, wherein: each of the low-frequency driving circuits has a first switch, coupled to the corresponding first data line, with a first gate terminal coupled to the corresponding first gate line; and each of the high-frequency driving circuits has a second switch, coupled to the corresponding second data line, with a second gate terminal coupled to the corresponding second gate line.

12. A method of driving a liquid crystal display (LCD) comprising: providing an LCD having a plurality of pixel elements arranged in an array, and a plurality of driving circuits for driving the plurality of pixel elements; driving a first sub-region of each of the pixel elements at a first driving frequency; and driving a second sub-region of each of the pixel elements at a second driving frequency different than the first driving frequency; wherein the first sub-regions exhibit a different size than the second sub-regions.

13. The method of claim 12, wherein the second driving frequency is a multiple of the first driving frequency.

14. An LCD system, comprising: a pixel element having a first sub-region and a second sub-region; a low-frequency driving circuit disposed on the first sub-region; a high-frequency driving circuit disposed on the second sub-region; a plurality of date lines, with a first of the date lines being coupled to the low-frequency driving circuit and a second of the data lines being coupled to the high-frequency driving circuit; and a plurality of gate lines, with a first of the gate lines being coupled to the low-frequency driving circuit and a second of the gate lines being coupled to the high-frequency driving circuit.

15. The LCD system of claim 14, further comprising: a first substrate; a second substrate; a liquid crystal material disposed between the first substrate and the second substrate; a first electrode disposed on the first substrate; and a second electrode disposed on the second substrate; wherein the first electrode corresponds to the first sub-region and is coupled to the low-frequency driving circuit, and the second electrode corresponds to the second sub-region and is coupled to the high-frequency driving circuit.

16. The LCD system of claim 14 further comprising: a first substrate; a first electrode disposed on the first substrate; and a second electrode disposed on the first substrate; wherein the first electrode corresponds to the first sub-region and is coupled to the low-frequency driving circuit, and the second electrode corresponds to the second sub-region and is coupled to the high-frequency driving circuit.

17. A method of driving an LCD having a plurality of pixel elements arranged in an array, the method comprising: driving a first sub-region of each of the pixel elements, at a first driving frequency, according to a first data signal communicated by a first data line; and driving a second sub-region of each of the pixel elements, at a second driving frequency different than the first driving frequency, according to a second data signal communicated by a second data line.

18. The method of claim 17, wherein the first sub-regions are smaller than the second sub-regions.

19. The method of claim 17, wherein the plurality of pixel elements comprises blue phase liquid crystal.

20. The method of claim 17, wherein the second driving frequency is a multiple of the first driving frequency.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a diagram illustrating temperature dependent Kerr constants of a representative polymer stabilized blue phase liquid crystal mixture (BP07) at different driving frequencies.

[0023] FIG. 2 is a schematic diagram of an embodiment of an LCD system.

[0024] FIG. 3 is a schematic diagram of an embodiment of a pixel.

[0025] FIG. 4 is a schematic, side view of an embodiment of an LCD system.

[0026] FIG. 5 is a diagram illustrating simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 4.

[0027] FIG. 6 is a schematic, side view of another embodiment of an LCD system.

[0028] FIG. 7 is a diagram illustrating simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 6.

[0029] FIG. 8 is a flowchart illustrating basic operations in accordance with an embodiment.

[0030] FIG. 9 is a schematic diagram of an embodiment of a pixel element.

[0031] FIG. 10 is a flowchart illustrating basic operations in accordance with another embodiment.

[0032] FIG. 11 is a signal diagram depicted representative gate control and data signals that can be used in an example embodiment.

[0033] FIG. 12 is a schematic, side view of another embodiment of an LCD system.

[0034] FIG. 13 is a diagram illustrating simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 12.

DETAILED DESCRIPTION

[0035] For ease in explanation, the following discussion describes embodiments of the present disclosure in the context of an LCD system. It is to be understood that the invention is not limited in its application to the details of the particular arrangements shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.

[0036] In this regard, LCD systems and related methods with pixel elements driven at different frequencies are provided. As will be described in greater detail below, such systems and methods may involve the use of large Δ∈ LC materials (e.g., PS-BPLCD) that exhibit reduced temperature sensitivity. The preferred embodiments of the present invention will now be described with reference to the drawings.

[0037] With reference to FIG. 2, an embodiment of an LCD system 100 is depicted. Fundamentally, LCD system 100 includes an LCD panel 110 with a plurality of pixels, data control circuitry 120 and gate control circuitry 130. The circuits and functions in the embodiments of the present invention can be implements by hardware, software or a combination of hardware and software such as microcontrollers, application-specific integrated circuits (ASIC) and programmable microcontrollers.

[0038] In keeping with the description of FIG. 2, LCD panel 110 incorporates a plurality of pixels (typically thousands of pixels, e.g., pixels 140, 150), which are arranged in a two-dimensional array comprising a plurality of rows and columns. For ease in illustration, only a few pixels are illustrated in FIG. 2. As is known, in a thin film transistor (TFT) LCD panel, a pixel is typically formed from three pixel elements (PEs): one red, one green, and one blue, although various configurations may be used. For instance, pixel 150 is depicted as including three PEs—PE(R), PE(G) and PE(B). One or more transistors and one or more storage capacitors are typically coupled to each pixel element, thereby forming driving circuitry for the associated pixel element.

[0039] The transistors of all pixels in a given row typically have their gate electrodes connected to a gate line (e.g., line 152), and their source electrodes connected to a data line (e.g., line 154). The gate control circuitry 130 and data control circuitry 120 control the voltage applied to the respective gate and data lines to individually address each pixel element in the LCD panel. By controllably pulsing the respective pixel element driving transistors, the driving circuits can control the transmissivity of each PE, and thereby control the color of each pixel. The storage capacitors assist in maintaining the charge across each pixel between successive pulses (which are delivered in successive frames).

[0040] An embodiment of a pixel 150 that may be implemented in an LCD system (such as LCD system 100 of FIG. 1) is depicted schematically in FIG. 3. As shown in FIG. 3, pixel 150 incorporates three PEs—a red PE, a green PE and a blue PE, denoted by PE(R), PE(G) and PE(B), respectively. Each of the PEs is divided into two sub-regions that share the structural components of a PE (e.g., a corresponding color filter). Additionally, each sub-region is associated with a dedicated driving circuit. Specifically, PE(R) includes sub-regions 162, 164, PE(G) includes sub-regions 172, 174, and PE(B) includes sub-regions 182, 184. The sub-regions 162, 164, 172, 174, 182 and 184 are associated with driving circuits 163, 165, 173, 175, 183 and 185, respectively. Notably, driving circuits 163, 173 and 183 operate at a different driving frequency (f.sub.1) than the driving frequency (f.sub.2) of driving circuits 165, 175 and 185.

[0041] In some embodiments, driving circuits 163, 173 and 183 can be configured as low-frequency driving circuits for operating at a driving frequency lower than the driving frequency of driving circuits 165, 175 and 185 (thus, becoming high-frequency driving circuits). By way of example, the low-frequency driving circuits are driven at 120 Hz and the high-frequency driving circuits are driven at 360 Hz. Preferably, the driving frequencies of the driving circuits are in the range of approximately 60 Hz to approximately 480 Hz. Other frequencies also are applicable (e.g., 1200 Hz), however, such frequencies may introduce issues (e.g., charging issues). Additionally, the driving frequency of the high-frequency driving circuits is preferably a multiple of the driving frequency of the low-frequency driving circuits (e.g., 120 Hz*3=360 Hz).

[0042] Each of sub-regions 162, 172 and 182 (although similar in size with respect to each other) are different in size than the sub-regions 164, 174 and 184. In this embodiment, sub-regions 162, 172 and 182 are smaller in size (i.e., correspond to a smaller area when viewed in plan view) than sub-regions 164, 174 and 184. Preferably, the ratio of the areas of the sub-regions for a PE is in the range of 1 to approximately 10, although other ratios may be used. For example, the ratio of the area of the sub-region 162 to the sub-region 164 is 1:2 and as a result the area of the sub-region 162 is smaller than the sub-region 164. In another case, the ratio of the area of the sub-region 162 to the sub-region 164 is 0.1:1 and as a result the area of the sub-region 162 is bigger than the sub-region 164. In other case, the ratio of the area of the sub-region 162 to the sub-region 164 is 1:1 and as a result the area of the sub-region 162 is equal to the sub-region 164. In some embodiments, the size of the larger sub-regions is at least approximately 2 times the size of the smaller sub-regions. It should be noted that the selection of sub-region sizes (as with driving frequency) may be based on a variety of factors such as LC materials, electrode structures, and required working temperature range, among others.

[0043] In the embodiment of FIG. 3, the smaller sub-regions 162, 172 and 182 are driven by the associated driving circuits at lower driving frequencies than the frequencies used for driving the larger sub-regions 164, 174 and 184. In other embodiments, the smaller sub-regions are driven at higher driving frequencies than the frequencies used for driving the larger sub-regions. In such an embodiment, however, the working temperature range will likely be influenced more by low frequency driving since the area of the sub-regions driven by the low-frequency driving circuits would be larger than that driven by the high-frequency driving circuits.

[0044] FIG. 4 is a schematic, side view of an embodiment of an LCD system 200 that includes sub-regions 202 and 204, with the sub-regions being operated at different driving frequencies. In particular, sub-region 202 is driven at high frequency (HF) and sub-region 204 is driven at low frequency (LF).

[0045] As shown in FIG. 4, LCD system 200 is configured as an in-plane switching (IPS) LCD panel that incorporates an upper substrate 210, a lower substrate 212 and a large Δ∈ LC mixture 214 sandwiched between the substrates. It should be noted that for TFT-grade nematic LCs, dielectric anisotropy is usually Δ∈<10 in order to obtain low viscosity. However, for blue phase LCDs, in order to reduce operation voltage, an LC host with Δ£>50 is often chosen—a large Δ∈ LC mixture. Some commercially available blue phase LC hosts exhibit Δ∈>100.

[0046] LC mixture 214 includes liquid crystal molecules that exhibit optical isotropicity. In this embodiment, the liquid crystal molecules are BPLC, with BP07 (Δ∈˜300) being used as the BP host. However, in other embodiments, various other large Δ∈ LC mixtures may be used, such as uniformly standing helix LCs, uniformly lying helix LCs or other LC modes, for example.

[0047] Sub-regions 202 and 204 exhibit equal lengths (l.sub.1=l.sub.2), with the electrodes being formed on lower substrate 212. The electrodes (e.g., electrodes 221, 222, 223 and 224) exhibit the same width/gap and the same height. For example, the width/gap is 3 μm/10 μm and the protrusion height is 3.5 μm. It should be noted that, in other embodiments, various other electrode configurations may be used, such as fringe-field switching (FFS) and vertical field switching (VFS), for example.

[0048] To reduce the temperature sensitivity of Kerr constant, pixels of sub-region 202 are operated at a higher driving frequency (or frame rate) than the driving frequency of pixels of sub-region 204. Since the optimal temperature (T.sub.op) with highest Kerr constant is different for each frequency (e.g., 8° C. for 120 Hz and 18° C. for 360 Hz), by combining sub-regions 202 and 204, the pixels of the LCD panel exhibit wider working temperature ranges.

[0049] FIG. 5 illustrates simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 4. As shown in FIG. 5, for single frequency driving (e.g. 120 Hz or 360 Hz), the temperature range (V.sub.op+1.0 V) is about 10° C., which is much narrow for regular usage. But when dual frame rates are employed, the temperature range nearly doubles, including the room temperature. Moreover, the device parameters (e.g., areas of sub-pixels, electrode structures, protrusion height of electrodes, etc.) could be optimized to further enlarge the temperature range. Also, if higher driving frequency is acceptable, then better performance could be obtained.

[0050] FIG. 6 is a schematic, side view of another embodiment of an LCD system 250 configured as an IPS LCD panel that incorporates an upper substrate 260, a lower substrate 262 and a large Δ∈ LC mixture 264 (e.g., BP07) sandwiched between the substrates. As shown in FIG. 6, the LCD system 250 is divided into two sub-regions 252 and 254, with sub-region 252 (HF sub-region) being operated at a higher driving frequency than the driving frequency of sub-region 254 (LF sub-region).

[0051] Sub-regions 252 and 254 exhibit different lengths (l.sub.1≠l.sub.2, and l.sub.1:l.sub.2=4:1) and different electrode configurations. In particular, the electrodes are formed on lower substrate 262, with electrodes of sub-region 252 (e.g., electrodes 271, 272) exhibiting a width/gap of 3 μm/10 μm, and electrodes of sub-region 254 (e.g., electrodes 281, 282) exhibiting a width/gap of 3 μm/8.5 μm. Height of the electrodes is 3.5 μm for both sub-regions.

[0052] FIG. 7 illustrates simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 6. As can be seen, the optimal temperature range is widened compared to that shown in FIG. 5. Potentially more significantly, the range is shifted to high temperature, where room temperature (22° C.) is centered. As such, this performance may be more preferable for commercial applications.

[0053] FIG. 8 is a flowchart illustrating basic operations in accordance with an embodiment. As shown in FIG. 8, the functionality (or method) associated with driving an LCD is construed as beginning at block 300, in which an LCD is provided. In particular, the LCD includes a plurality of pixel elements arranged in an array having a plurality of columns and a plurality of rows, and a plurality of driving circuits for driving the plurality of pixel elements. In some embodiments, each of the plurality of pixel elements is associated with two driving circuits. An example embodiment of a pixel element with two driving circuits will be described in detail with respect to FIG. 9.

[0054] In block 302, a first sub-region of each of the pixel elements is driven at a first driving frequency, such as is performed by a first driving circuit. In block 304, a second sub-region of each of the pixel elements is driven at a second driving frequency different than the first driving frequency. This is performed by a second driving circuit. Notably, the first sub-region of each of the pixel elements exhibits the first size and the second sub-region of each of the pixel elements exhibits the second size different than the first size. Thus, in some embodiments, the larger sub-regions are driven at higher frequencies than the driving frequencies of the smaller sub-regions while, in other embodiments, the larger sub-regions are driven at lower frequencies than the smaller sub-regions.

[0055] FIG. 9 is a schematic diagram of an embodiment of a pixel element (PE) 310 that incorporates an LF sub-region 311 and an HF sub-region 331 associated with LF driving circuit 312 and HF driving circuit 332, respectively. LF driving circuit 312 includes a switch 314, a storage capacitor (C.sub.ST) 316 and a liquid crystal capacitor (C.sub.LC) 318. Switch 314 includes a first terminal 320, a second terminal 322 and a gate terminal 324. The first terminal 320 is coupled to a first data line 326 for receiving a first data signal. The capacitors 316 and 318 are coupled in parallel to the second terminal 322. The gate terminal 324 is coupled to a first gate line 328 for receiving a first gate control signal.

[0056] HF driving circuit 332 includes a switch 334, a storage capacitor (C.sub.ST) 336 and a liquid crystal capacitor (C.sub.LC) 338. Switch 334 includes a first terminal 340, a second terminal 342 and a gate terminal 344. The first terminal 340 is coupled to a second data line 346 for receiving a second data signal. The capacitors 336 and 338 are coupled in parallel to the second terminal 342. The gate terminal 344 is coupled to a second gate line 348 for receiving a second gate control signal.

[0057] In this embodiment, the switches 314 and 334 are transistors (e.g., TFTs) that are turned on when the respective gate terminals receive an enabling signal. The liquid crystal capacitors 318 and 338 are formed by BPLC, for example.

[0058] In operation, LF driving circuit 312 and HF driving circuit 332 are driven a different frequencies (e.g., 120 HZ and 360 Hz, respectively). Specifically, gate lines 328, 348 are pulsed at corresponding driving frequencies to enable respective gate terminals 324 and 344. By pulsing the driving switches 314 and 334 at the corresponding frequencies, the driving circuits 312 and 332 control the transmissivity of associated sub-regions of PE 310 in accordance with data signals provided by data lines 326 and 346. As such, the LC mixture used in the PE exhibits reduced temperature sensitivity and a widened working temperature range.

[0059] It should be noted that the use of two data lines per PE (such as depicted in FIG. 9) may be preferable in some embodiments. Specifically, TFTs are typically AC-driven, which presents the potential for sub-region to sub-region crosstalk as the polarity of the voltage applied to a sub-region may be inverted with respect to another sub-region. Use of the independent data lines for each sub-region of a PE may alleviate this issue.

[0060] It should also be noted that, although each of the driving circuits of the embodiment of FIG. 9 is a standard one transistor and two capacitor (1T2C) circuit, other circuit configurations (such as modified 1T2C TFT, 2T3C TFT, and 4T2C TFT, among others) may be used in other embodiments.

[0061] FIG. 10 is a flowchart illustrating basic operations in accordance with another embodiment, such as the embodiment depicted in FIG. 9. As shown in FIG. 10, the functionality (or method) associated with driving an LCD is construed as beginning at block 350, in which an LCD having a plurality of pixel elements arranged in an array is provided. In block 352, a first sub-region of each of the pixel elements is driven, at a first driving frequency, according to a first data signal communicated by a first data line.

[0062] By way of example, the diagram of FIG. 11 depicts representative signals that may be used. In particular, FIG. 11 shows a first data signal (Data-1) and a corresponding first gate control signal (Gate-1), as well as a second data signal (Data-2) and a corresponding second gate control signal (Gate-2). In operation, with respect to the functionality of block 352, the first gate control signal pulses a driving switch associated with the first sub-region to control the transmissivity of the first sub-region in accordance with the first data signal.

[0063] In block 354, a second sub-region of each of the pixel elements is driven, at a second driving frequency different than the first driving frequency, according to a second data signal communicated by a second data line. For instance, the second gate control signal (Gate-2) is used to pulse a driving switch associated with the second sub-region to control the transmissivity of the second sub-region in accordance with the second data signal (Data-2). Note that, in the embodiment of FIG. 11, the second driving frequency is higher than the first driving frequency.

[0064] FIG. 12 is a schematic, side view of another embodiment of an LCD system 400 configured as LCD panel that incorporates an upper substrate 410, a lower substrate 412 and a large Δ∈ LC mixture 414 (e.g., BP07) sandwiched between the substrates. As shown in FIG. 12, the LCD system 400 is divided into two sub-regions 422 and 424, with sub-region 422 (HF sub-region) being operated at a higher driving frequency than the driving frequency of sub-region 424 (LF sub-region).

[0065] In this embodiment, first pixel elements 430 and corresponding pixel electrodes (e.g., electrode 431) are disposed on upper substrate 410, and second pixel elements 432 and corresponding pixel electrodes (e.g., electrode 433) are disposed on lower substrate 412.

[0066] Simulated temperature dependent operation voltages for different driving frequencies (120 Hz and 360 Hz) and frequency combination (120 Hz+360 Hz) based on the embodiment of FIG. 12 are illustrated in the graph of FIG. 13. Since the light goes through the LF and HF regions (lower and upper) separately and consecutively, the effective Kerr constant would be the sum of these two layers, which means:

Δn.sub.ind=Δn.sub.ind-1+Δn.sub.ind-2=λ(K.sub.1+K.sub.2)E.sup.2.  (4)

[0067] Therefore, apart from the wider temperature range, the operation voltage is decreased (<15V) for this embodiment. As is shown, low operation voltage is good for charging, meanwhile voltage less than 15V enables one thin-film transistor (TFT) driving on each substrate. Thus, low cost and ease of driving may be achieved.

[0068] The embodiments described above are illustrative of the invention and it will be appreciated that various permutations of these embodiments may be implemented consistent with the scope and spirit of the invention.