JP2014132355A - Liquid crystal display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make pixels smaller in size than pixels each using two SRAMs in each pixel, and to perform a stable operation even when two SRAMs are prepared in each pixel.SOLUTION: In a pixel 12A, data output to a column data line (d) is sampled by a switch SW11 and written to an SRAM 121. Data is written to SRAMs 121 of all pixels 12A constituting an image display part. Then switches SW12 of all the pixels 12A are turned on thereafter with a trigger pulse, and data of the SRAMs 121 are transferred together to a capacitor C1 constituting a DRAM 202 to be held and also applied to a reflection electrode PE. A pixel 12A comprises seven transistors 1 and one capacitor C1, so the pixel can comprise a very small number of components, and the SRAMs 121, DRAM 202, and reflection pixel PE are arranged effectively in the height direction of the element to make the pixels small in size.

Description

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that performs gradation display by a combination of a plurality of subframes according to a gradation level represented by a plurality of bits.

Conventionally, a sub-frame driving method is known as one of halftone display methods in a liquid crystal display device. In the subframe driving method, which is a type of time axis modulation method, a predetermined period (
For example, in the case of a moving image, one frame which is a display unit of one image) is divided into a plurality of subframes, and pixels are driven by a combination of subframes corresponding to the gradation to be displayed. The gradation to be displayed is determined by the ratio of the pixel driving period in a predetermined period, and this ratio is specified by a combination of subframes.

In this sub-frame driving type liquid crystal display device, each pixel is known to be composed of a master latch and a slave latch, a liquid crystal display element, and a total of three switching transistors (first to third) ( For example, see Patent Document 1). In this pixel, the master latch applies 1-bit first data to one of the two input terminals through the first switching transistor and is complementary to the first data on the other input terminal. When the second data having the same relationship is applied through the second switching transistor and the pixel is selected by the row selection signal applied through the row scanning line, the first and second switching transistors described above are used. Is turned on to write the first data. For example, when the first data has a logical value “1” and the second data has a logical value “0”, the pixel performs display.

After each data is written to all the pixels by the same operation as described above, the third switching transistors of all the pixels are turned on within the subframe period, and the data written to the master latch is simultaneously read and read to the slave latch. The data latched by the slave latch is applied from the slave latch to the pixel electrode of the liquid crystal display element. Thereafter, the above operation is repeated for each subframe, and a desired gradation display is performed by combining all subframes within one frame period.

That is, in the sub-frame driving type liquid crystal display device, all the sub-frames in one frame period are assigned in advance to the same period or different predetermined periods, and at the time of maximum gradation display in each pixel. Display is performed in all subframes. In the case of the minimum gradation display, no display is performed in all subframes. In the case of other gradations, the subframe to be displayed is selected according to the display gradation. In this conventional liquid crystal display device, the input data is digital data indicating a gradation, and it is also a digital driving system having a two-stage latch configuration.

JP-T-2001-523847

However, in the conventional liquid crystal display device, the two latches in each pixel are respectively
Since it is composed of a static random access memory (SRAM), the number of transistors increases and it is difficult to reduce the pixel size. Further, when the above two latches are configured by SRAM, the specific circuit configuration of the SRAM and the switching transistor capable of stable operation is not disclosed in the above-mentioned Patent Document 1.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device capable of downsizing the pixel as compared with a pixel using two SRAMs in the pixel.

Another object of the present invention is to provide a liquid crystal display device including pixels that can perform stable operation even in a configuration in which two SRAMs are prepared in each pixel.

In order to achieve the above object, in the liquid crystal display device of the first invention, each of a plurality of pixels provided at intersections where a plurality of column data lines and a plurality of row scanning lines intersect,
A display element in which liquid crystal is filled and sealed between the opposing pixel electrode and the common electrode, and each sub for displaying each frame of the video signal in a plurality of sub-frames having a display period shorter than one frame period of the video signal The first switching means for sampling the frame data via the column data line, and the static random access memory together with the first switching means, and the subframe data sampled by the first switching means A dynamic random access memory is configured together with a first signal holding means for storing data, a second switching means for outputting the subframe data stored in the first signal holding means, and a second switching means. And stored in the first signal holding means supplied through the second switching means Memory content is rewritten in a sub-frame data, and a second signal holding means to be applied to the pixel electrode of the output data,
Of the plurality of pixels constituting the image display unit, the first subframe data is set for each row-unit pixel.
After writing to all of the plurality of pixels by repeatedly writing to the signal holding means, the second switching means for all of the plurality of pixels is turned on by the trigger pulse, and the subframe stored in the first signal holding means is stored. It has a pixel control means which performs the operation | movement which rewrites the memory content of the 2nd signal holding means of a some pixel with data for every sub-frame.

In order to achieve the above object, in the liquid crystal display device of the second invention, the second signal holding means is constituted by a capacitor, and the second switching means is switched by two trigger pulses having opposite polarities. It is characterized by comprising a controlled transmission gate.

In order to achieve the above object, in the liquid crystal display device of the third invention, the first switching means is constituted by one first transistor, and the first signal holding means has the output terminals of the other input terminals. The first and second inverters connected to the terminals, and of the first and second inverters, driving the second transistor constituting the first inverter on the input side as viewed from the first transistor The force is set to be larger than the driving force of the third transistor constituting the second inverter on the output side as viewed from the first transistor, and the driving force of the first transistor constitutes the second inverter. The driving power of the third transistor is set larger than that of the third transistor.

In order to achieve the above object, in the liquid crystal display device of the fourth invention, a multilayer wiring layer is formed above a substrate on which two transistors constituting a transmission gate are formed. Among them, a capacitor is formed by an electrode formed between one intermediate wiring layer and an interlayer insulating film, and a pixel electrode is formed by the uppermost wiring layer of the multilayer wiring layer.

In order to achieve the above object, a liquid crystal display device according to a fifth aspect of the present invention is a cross section where a plurality of sets of column data lines and a plurality of row scanning lines intersect each other. Each of the plurality of pixels provided in the
A display element in which liquid crystal is filled and sealed between the opposing pixel electrode and the common electrode, and normal rotation for displaying each frame of the video signal in a plurality of subframes having a display period shorter than one frame period of the video signal. First switching means for sampling subframe data via one column data line of a set of two column data lines, and inverted subframe data having a relationship of reverse logical value to normal rotation subframe data Is switched via the other column data line of the set of two column data lines, and the normal subframe data and the inversion sampled by the first and second switching units, respectively. The sub-frame data is stored in the first and second inverters, each of which has an output terminal connected to the other input terminal. A first signal holding means that constitutes a first static random access memory together with the switching means, and a first subframe data output from a connection point between the first signal holding means and the first switching means. Third switching means, a fourth switching means for outputting inverted subframe data from a connection point between the first signal holding means and the second switching means, and a third switching means supplied through the third and fourth switching means. The stored contents are rewritten with the normal subframe data and the inverted subframe data stored in one signal holding means, and the output data is applied to the pixel electrode. The third output terminal is connected to the other input terminal. And a fourth inverter, together with the third and fourth switching means, the second static random access And a second signal holding means constituting the memory,
A second output terminal connected to the first switching means of the first and second inverters;
Is set to be smaller than the driving force of the first inverter whose output terminal is connected to the second switching means, and the driving force of the first and second inverters is the third driving force.
And the driving power of the fourth inverter is set to be greater than the driving power of the fourth inverter, and among the plurality of pixels constituting the image display unit, the forward subframe data and the inverted subframe data are set to the first signal for each row-unit pixel After repeating writing to the holding means and writing to all of the plurality of pixels, the third and fourth switching means of all of the plurality of pixels are turned on by the trigger pulse, and the positive signal stored in the first signal holding means is stored. It has a pixel control means for performing the operation of rewriting the storage contents of the second signal holding means of a plurality of pixels for each subframe by the inverted subframe data and the inverted subframe data.

Furthermore, in order to achieve the above object, in the liquid crystal display device of the sixth invention, each of the plurality of pixels provided at the intersections where the plurality of column data lines and the plurality of row scanning lines intersect,
A display element in which liquid crystal is filled and sealed between the opposing pixel electrode and the common electrode, and each sub for displaying each frame of the video signal in a plurality of sub-frames having a display period shorter than one frame period of the video signal A first switching means composed of one transistor for sampling frame data via a column data line and a sub-frame data sampled by the first switching means for storing each other's output terminals on the other input A first signal holding means comprising a first and a second inverter connected to a terminal and constituting a first static random access memory together with the first switching means; and storing in the first signal holding means A second transistor composed of one transistor for outputting the subframe data that has been processed
The storage contents are rewritten with the subframe data stored in the first signal holding means supplied through the switching means and the first switching means, and the output data is applied to the pixel electrode. A second signal holding means comprising a third and a fourth inverter connected to the input terminal and constituting a second static random access memory together with the second switching means;
A second output terminal connected to the first switching means of the first and second inverters;
The driving power of the inverter is set to be smaller than the driving power of the first inverter and set to be smaller than the driving power of the transistors constituting the first switching means. The driving power of the fourth inverter whose output terminal is connected to the second switching means is set to be smaller than the driving power of the third inverter, and more than the driving power of the transistors constituting the second switching means. And the driving power of the first inverter is set to be larger than the driving power of the fourth inverter,
Of the plurality of pixels constituting the image display unit, the first subframe data is set for each row-unit pixel.
After writing to all of the plurality of pixels by repeatedly writing to the signal holding means, the second switching means for all of the plurality of pixels is turned on by the trigger pulse, and the subframe stored in the first signal holding means is stored. It has a pixel control means which performs the operation | movement which rewrites the memory content of the 2nd signal holding means of a some pixel with data for every sub-frame.

According to the present invention, the size of the pixel can be reduced as compared with the conventional liquid crystal display device using two SRAMs in the pixel. In addition, according to the present invention, even when two SRAMs are prepared in a pixel, a stable operation can be performed as compared with a conventional liquid crystal display device.

1 is an overall configuration diagram of an embodiment of a liquid crystal display device of the present invention. 1 is a circuit diagram of a first embodiment of a pixel which is a main part of the present invention. It is a circuit diagram of an example of an inverter. FIG. 3 is a cross-sectional structure diagram of an example of one pixel shown in FIG. 2. 3 is a timing chart for explaining the operation of a pixel in the liquid crystal display device of the present invention. It is explanatory drawing which multiplexes the saturation voltage of the liquid crystal of a liquid crystal display device, and the threshold voltage of a liquid crystal as binary weighted pulse width modulation data. It is a circuit diagram of a second embodiment of a pixel which is a main part of the present invention. It is a figure explaining the magnitude relationship of the driving force between each inverter which comprises two SRAM of FIG. FIG. 6 is a circuit diagram of a third embodiment of a pixel which is a main part of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of a liquid crystal display device according to the present invention. In the figure, a liquid crystal display device 10 according to the present embodiment includes an image display unit 11 in which a plurality of pixels 12 are regularly arranged, a timing generator 13, a vertical shift register 14, a data latch circuit 15, a horizontal And a driver 16. Further, the horizontal driver 16 includes a horizontal shift register 161, a latch circuit 162, and a level shifter / pixel driver 163.

The image display unit 11 is connected to the vertical shift register 14 at one end and extends in the row direction (X direction) with m (m is a natural number of 2 or more) row scanning lines g1 to gm, and a level shifter / pixel driver 163. Are provided at each intersection where n (n is a natural number of 2 or more) column data lines d1 to dn extending at one end and extending in the column direction (Y direction) are arranged in a two-dimensional matrix. Was
It has m × n pixels 12 in total. The present invention is characterized by the circuit configuration of the pixel 12, and embodiments thereof will be described later. All the pixels 12 in the image display unit 11 are commonly connected to a trigger line trig having one end connected to the timing generator 13.

In FIG. 1, the column data lines indicate n column data lines d1 to dn. However, the normal data column data line dj and the inverted data column data line dbj are set as one set in total. A set of column data lines may be used. The normal rotation data transmitted by the normal data column data line dj and the reverse data transmitted by the reverse data column data line dbj are 1-bit data that is always in the relationship of the inverse logical value (complementary relationship). is there. Further, although only one trigger line trig is shown in FIG. 1, there are cases where two trigger lines including a normal trigger pulse trigger line trig and an inverted trigger pulse trigger line trigb are used. The forward trigger pulse transmitted by the forward trigger pulse trigger line trig and the inverted trigger pulse transmitted by the inverted trigger pulse trigger line trigb are always in the relationship of a reverse logical value (complementary relationship).

The timing generator 13 receives the vertical synchronization signal Vst and the horizontal synchronization signal H from the host device 20.
External signals such as st and basic clock CLK are received as input signals, and based on these external signals, AC signal FR, V start pulse VST, H start pulse HST, clock signals VCK and HCK, latch pulse LT, trigger pulse TRI Various internal signals such as are generated.

Among the above internal signals, the alternating signal FR is a signal whose polarity is inverted every subframe, and a common electrode voltage Vcom described later is applied to the common electrode of the liquid crystal display element in the pixel 12 constituting the image display unit 11. Supplied as The start pulse VST is a pulse signal output at the start timing of each subframe to be described later, and switching of subframes is controlled by the start pulse VST. The start pulse HST is applied to the horizontal shift register 161.
It is a pulse signal output at the start timing to be input. The clock signal VCK is a shift clock that defines one horizontal scanning period (1H) in the vertical shift register 14;
The vertical shift register 14 performs a shift operation at the timing of VCK. Clock signal HCK
Is a shift clock in the horizontal shift register 161, and is a signal for shifting data with a 32-bit width.

The latch pulse LT is a pulse signal that is output at a timing when the horizontal shift register 161 has shifted the data for the number of pixels in one row in the horizontal direction. The trigger pulse TRI is
This is a pulse signal supplied to all the pixels 12 in the image display unit 11 through the trigger line trig. This trigger pulse TRI is the first in each pixel 12 in the image display unit 11 within the subframe period.
Is output immediately after the data is sequentially written to the signal holding means, and the data of the first signal holding means of all the pixels 12 in the image display unit 11 is held in the same pixel within the subframe period. Transfer to the means at once.

The vertical shift register 14 transfers the V start pulse VST supplied at the beginning of each subframe in accordance with the clock signal VCK, and sequentially supplies the row scanning signals to the row scanning lines g1 to gm sequentially in 1H units. To do. As a result, row scanning lines are sequentially selected in units of 1H from the uppermost row scanning line g1 to the lowermost row scanning line gm in the image display unit 11.

The data latch circuit 15 latches 32-bit width data divided for each subframe supplied from an external circuit (not shown) based on the basic signal CLK from the host device 20, and then synchronizes with the basic signal CLK. To the horizontal shift register 161. In this embodiment, one frame of a video signal is divided into a plurality of subframes having a display period shorter than one frame period of the video signal, and gradation display is performed by a combination of subframes.
The external circuit converts the gradation data indicating the gradation for each pixel of the video signal into 1-bit subframe data for each subframe unit for displaying the gradation of each pixel in the entire plurality of subframes. Convert. The external circuit further combines the sub-frame data for 32 pixels in the same sub-frame into the data latch circuit 1 as the 32-bit width data.
5 is supplied.

When viewed in the processing system of 1-bit serial data, the horizontal shift register 161 starts shifting by the H start pulse HST supplied from the timing generator 13 at the beginning of 1H, and has a 32-bit width supplied from the data latch circuit 15. Data is clock signal HC
Shift in sync with K. The latch circuit 162 performs horizontal shift according to the latch pulse LT supplied from the timing generator 13 when the horizontal shift register 161 has finished shifting n bits of data equal to the number of pixels n for one row of the image display unit 11. Register 161
N-bit data supplied in parallel (ie, sub-frame data for n pixels in the same row) is latched and output to the level shifter of the level shifter / pixel driver 163. When the data transfer to the latch circuit 162 is completed, the H start pulse is output again from the timing generator 13, and the horizontal shift register 161 resumes shifting the 32-bit width data from the data latch circuit 15 in accordance with the clock signal HCK.

The level shifter of the level shifter / pixel driver 163 shifts the signal level of n subframe data corresponding to n pixels in one row supplied by being latched by the latch circuit 162 to the liquid crystal drive voltage. The pixel driver of the level shifter / pixel driver 163 is
N subframe data corresponding to n pixels in one row after the level shift are transferred to n data lines d.
1 to dn are output in parallel.

The horizontal shift register 161, the latch circuit 162, and the level shifter / pixel driver 163 constituting the horizontal driver 16 output data for a pixel row to which data is written this time in 1H, and data for a pixel row to which data is written in the next 1H. Shift in parallel. In a certain horizontal scanning period, the latched n sub-frame data for one row are simultaneously output in parallel to the n data lines d1 to dn as data signals.

Among a plurality of pixels 12 constituting the image display unit 11, n pixels 12 in one row selected by the row scanning signal from the vertical shift register 14 are one row output from the level shifter / pixel driver 163 all at once. N subframe data are sampled via n data lines d1 to dn and written in first signal holding means (to be described later) in each pixel 12.

Next, each embodiment of the pixel 12 of the main part of the liquid crystal display device of the present invention will be described in detail.

FIG. 2 shows a circuit diagram of a first embodiment of a pixel which is a main part of the present invention. In the figure,
The pixel 12A of the present embodiment is a pixel provided at the intersection of any one column data line d and any one row scanning line g in FIG. 1, and constitutes a first switching means. Switch SW1
1 and first signal holding means (SM) 121, a static random access memory (SRAM) 201, and a switch SW1 constituting second switching means
2 and a second signal holding means (DM) 122, a dynamic random access memory (DRAM) 202, and a liquid crystal display element LC. The liquid crystal display element LC has a liquid crystal LC in a space between the reflective electrode PE and the common electrode CE that are arranged to face each other.
It is a known structure in which M is filled and enclosed.

The switch SW11 includes an N-channel MOS transistor (hereinafter referred to as an NMOS transistor) having a gate connected to the row scanning line g, a drain connected to the column data line d, and a source connected to the input terminal of the SM 121. ing. The SM 121 is a self-holding memory composed of two inverters INV11 and INV12 having one output terminal connected to the other input terminal. The input terminal of the inverter INV11 is the inverter INV
12 output terminals and the source of the NMOS transistor constituting the SW11. The input terminal of the inverter INV12 is connected to the switch SW12 and the output terminal of the inverter INV11. As shown in FIG. 3, the inverters INV11 and INV12 each have a P-channel MOS transistor (hereinafter referred to as a PMOS transistor) PTr and an NMOS transistor NTr in which the gates and drains are connected to each other.
However, each driving force is different.

That is, the inverter I on the input side constituting the SM 121 when viewed from the switch SW11.
The transistor in the NV 11 is a transistor having a larger driving force than the transistor in the inverter INV 12 on the output side constituting the SM 121 when viewed from the switch SW 11. Furthermore, the driving power of the NMOS transistor constituting the switch SW11 is
The inverter INV12 is configured by a transistor having a larger driving force than that of the NMOS transistor.

This is because when the data of SM121 is rewritten, particularly when the voltage a on the input side of switch SW11 of SM121 is at "L" level and the data sent via column data line d is at "H" level, inverter INV11. This is because it is necessary to make the voltage a higher than the input voltage at which is inverted. The voltage “a” at the “H” level is the NMOS constituting the inverter INV12.
It is determined by the ratio between the current of the transistor and the current of the NMOS transistor constituting the switch SW11. At this time, since the switch SW11 is an NMOS transistor, when the switch SW11 is on, the voltage on the VDD side of the power supplied via the column data line d is not input to the SM 121 by the threshold voltage Vth of the transistor. H ”level voltage is VDD
The voltage becomes lower by Vth. Moreover, since the voltage is driven near the Vth of the transistor, almost no current flows. That is, the higher the voltage a that conducts the switch SW11, the smaller the current that flows through the switch SW11.

That is, in order to reach a voltage higher than the voltage at which the transistor on the input side of the inverter INV11 inverts when the voltage a is “H” level, the current flowing through the switch SW11 causes the NMOS transistor constituting the transistor of the inverter INV12 on the output side to It needs to be larger than the flowing current. Accordingly, since the driving force of the NMOS transistor constituting the switch SW11 is configured to be larger than the driving force of the NMOS transistor constituting the inverter INV12, the transistor of the NMOS transistor constituting the switch SW11 in consideration of this. It is necessary to determine the size and the transistor size of the NMOS transistor constituting the inverter INV12.

The switch SW12 has a known transmission gate configuration including an NMOS transistor Tr1 and a PMOS transistor Tr2 whose drains are connected to each other and whose sources are connected to each other. The gate of the NMOS transistor Tr1 is connected to the normal trigger pulse trigger line trig, and the gate of the PMOS transistor Tr2 is connected to the inverted trigger pulse trigger line trigb.

The switch SW12 has one terminal connected to the SM 121 and the other terminal connected to the DM12.
2 and the reflective electrode PE of the liquid crystal display element LC. Therefore, switch S
W12 is turned on when the normal rotation trigger pulse supplied via the trigger line trig is at “H” level (in this case, the inverted trigger pulse supplied via the trigger line trigb is “L” level). Data stored in the SM 121 is read and transferred to the DM 122 and the reflective electrode PE. Further, the switch SW12 has a forward trigger pulse supplied via the trigger line trig at “L” level (in this case, the inverted trigger pulse supplied via the trigger line trigb is at “H” level).
In this case, it is turned off and the storage data of the SM 121 is not read.

Since the switch SW12 has a known transmission gate configuration including the NMOS transistor Tr1 and the PMOS transistor Tr2, the voltage in the range from GND to VDD can be turned on and off. That is, when the signals applied to the gates of the NMOS transistor Tr1 and the PMOS transistor Tr2 are at the GND side potential ("L" level), the PMOS transistor Tr2 cannot conduct, but the NMOS transistor Tr1 has a low resistance. Can be conducted. On the other hand, the gate input signal has a potential on the VDD side (“H”
Level), the NMOS transistor Tr1 cannot be turned on.
The S transistor Tr2 can conduct with a low resistance. Therefore, by controlling on / off of the transmission gate constituting the switch SW12 by the forward trigger pulse supplied via the trigger line trig and the inverted trigger pulse supplied via the trigger line trigb, The voltage range up to VDD can be switched with low resistance and high resistance.

The DM 122 is configured by a capacitor C1. Here, the data stored in SM121 and D
If the data stored in M122 is different, the switch SW12 is turned on, and SM12
When the storage data of 1 is transferred to the DM 122, the data held in the DM 122 is stored in the SM12.
It is necessary to replace with the stored data of 1.

When the retained data of the capacitor C1 constituting the DM 122 is rewritten, the retained data is changed by charging or discharging, and charging / discharging of the capacitor C1 is driven by an output signal of the inverter INV11. When the data held in the capacitor C1 is rewritten from “L” level to “H” level by charging, the output signal of the inverter INV11 is “H”.
11 (PTr in FIG. 3) is turned on, NMOS transistor (
Since NTr) in FIG. 3 is turned off, the capacitor C1 is charged by the power supply voltage VDD connected to the source of the PMOS transistor of the inverter INV11. On the other hand, when the data held in the capacitor C1 is rewritten from “H” level to “L” level by discharging, the inverter IN
The output signal of V11 is at "L" level, and at this time, NM constituting the inverter INV11
Since the OS transistor (NTr in FIG. 3) is turned on and the PMOS transistor (PTr in FIG. 3) is turned off, the accumulated charge in the capacitor C1 is discharged to GND through the NMOS transistor (NTr in FIG. 3) of the inverter INV11. Since the switch SW12 has an analog switch configuration using the above-described transmission gate, the capacitor C1 can be charged and discharged at high speed.

Further, in the present embodiment, the driving force of the inverter INV11 is set to be larger than the driving force of the inverter INV12, so that the capacitor C1 constituting the DM 122 can be charged / discharged at high speed. When the switch SW12 is turned on, the charge stored in the capacitor C1 also affects the input gate of the inverter INV12, but the inverter INV12
By setting the driving force of the inverter INV11 larger than
The charge / discharge of the capacitor C1 by the inverter INV11 is prioritized over the data input inversion of the NV12, and the stored data of the SM121 is not rewritten.

Note that the SRAM 201 and the DRAM 202 are each made up of a two-stage D comprising a capacitor and a switch.
Although a RAM configuration may be considered, in this case, when the capacitor used in place of the SM 121 and the capacitor constituting the DM are made conductive, charge neutralization occurs and the amplitude of the GND and VDD voltages cannot be taken. . On the other hand, according to the pixel 12A shown in FIG. 2, 1-bit data can be transferred from the SM 121 to the DM 122 with the amplitude of the GND and VDD voltages, and when driven by the same power supply voltage, the liquid crystal display element LC is applied. It becomes possible to set a high voltage, and a large dynamic range can be obtained.

In addition, the SRAM 201 is changed to a configuration including a capacitor and a switch, and the DRAM 202 is changed to an S
Although it is conceivable to change to RAM, in this case, there is a problem that the operation is unstable as compared with the pixel 12A of the present embodiment in FIG. That is, in the above configuration, it is necessary to rewrite data stored in the SRAM used in place of the DM 122 with the charge stored in the capacity used in place of the SM 121. Normally, however, the data holding of the memory by the SRAM is more than the charge holding capacity of the capacity. Since the capability is strong, there is a possibility that the charge of the capacitor used in place of the previous SM 121 is rewritten by the storage data of the SRAM used in place of the DM 122. Further, in this case, if the capacity used in place of the SM 121 is not rewritten by the post-stage SRAM data, it is necessary to increase the capacity, so that there is a problem that the pixel pitch increases and it is not suitable for pixel miniaturization.

According to the pixel 12A of the present embodiment shown in FIG. 2, as described above, the applied voltage of the liquid crystal display element LC can be set high, and only the effect that a large dynamic range can be obtained. In addition, the great effect that the pixel can be miniaturized can be obtained. The downsizing of the pixel is because the inverters INV11 and INV12 are each composed of two transistors, as shown in FIG. 2, and thus are composed of a total of seven transistors and one capacitor C1, which is more than the conventional pixel. In addition to the reason that a pixel can be configured by a small number of constituent elements, as described below, the reason is that SM 121, DM 122, and reflective electrode PE can be effectively arranged in the height direction of the element. .

FIG. 4 shows a cross-sectional configuration diagram of an embodiment of a pixel of a main part of a liquid crystal display device according to the present invention.
The capacitor C1 shown in FIG. 2 includes an MIM (Metal-Insulator-Metal) that forms a capacitor between wirings.
) A capacitance, a diffusion capacitance that forms a capacitance between the substrate and polysilicon, a PIP (Poly-Insulator-Poly) capacitance that forms a capacitance between two layers of polysilicon, and the like can be used. FIG.
Among these, the cross-sectional block diagram of a liquid crystal display device when the capacity | capacitance C1 is comprised by MIM is shown.

In FIG. 4, the PMOS transistor PTr11 of the inverter INV11 and the PMOS transistor Tr2 of the switch SW12, in which the drains are connected to each other by sharing a diffusion layer serving as a drain on the N well 101 formed in the silicon substrate 100, are provided. Is formed. Further, on the P-well 102 formed on the silicon substrate 100, the NMOS transistor NTr12 of the inverter INV12 and the NMOS transistor Tr1 of the switch SW12 are formed by sharing a diffusion layer serving as a drain to connect the drains. ing. Note that FIG. 4 does not show the NMOS transistor constituting the inverter INV11 and the PMOS transistor constituting the inverter INV12.

Further, above each of the transistors PTr11, Tr2, Tr1, and NTr12, an interlayer insulating film 105 is interposed between the metals, and the first metal 106, the second metal 108, and the third metal 1
10, an electrode 112, a fourth metal 114, and a fifth metal 116 are laminated. The fifth metal 116 constitutes a reflective electrode PE formed for each pixel. The diffusion layers constituting the sources of the NMOS transistor Tr1 and the PMOS transistor Tr2 constituting the switch SW12 are electrically connected to the first metal 106 by the contact 118, respectively, and further through the through holes 119a, 119b, 119c, 119e. The second metal 108, the third metal 110, the fourth metal 114, and the fifth metal 116 are electrically connected. That is, the NMOS transistor Tr1 and the PMOS transistor Tr constituting the switch SW12.
Each of the two sources is electrically connected to the reflective electrode PE.

Further, a passivation film (P) is formed on the reflective electrode PE (fifth metal 116) as a protective film.
SV) 117 is formed, and is spaced apart from the common electrode CE, which is a transparent electrode. Liquid crystal LCM is filled and sealed between the pixel electrode PE and the common electrode CE, and the liquid crystal display element LC
Is configured.

Here, an electrode 112 is formed on the third metal 110 via an interlayer insulating film 105. This electrode 112 is provided between the third metal 110 and the third metal 110 and the interlayer insulating film 10.
5 forms a capacitor C1. When the capacitor C1 is formed by the MIM, the SM 121, the switch SW11, and the switch SW12 are the transistor, the first metal 106, and the second metal 1
08, 1st and 2nd layer wiring, DM122 is MI using the third metal 110 at the top of the transistor
It can be formed with M wiring. Since the electrode 112 is electrically connected to the fourth metal through the through hole 119d, and the fourth metal 114 is further electrically connected to the reflective electrode PE through the through hole 119e, the capacitor C1 is a reflective electrode. Electrically connected to PE.

Light from a light source (not shown) passes through the common electrode CE and the liquid crystal LCM, is incident on the reflective electrode PE (fifth metal 116), is reflected, and travels backward through the original incident path and is emitted through the common electrode CE. .

According to the present embodiment, as shown in FIG. 4, the fifth metal 116, which is a five-layer wiring, is allocated to the reflective electrode PE, so that the SM 121 and DM 122 and the reflective electrode PE are effectively arranged in the height direction. Therefore, it is possible to reduce the pixel size. Thus, for example, pixels with a pitch of 3 μm or less can be configured with transistors having a power supply voltage of 3.3V. With this pixel of 3 μm pitch, a liquid crystal display panel having a diagonal length of 0.55 inches and a horizontal direction of 4000 pixels and a vertical direction of 2000 pixels can be realized.

Next, the operation of the liquid crystal display device 10 of FIG. 1 using the pixel 12A of the present embodiment will be described with reference to the timing chart of FIG.

As described above, in the liquid crystal display device 10 of FIG. 1, the row scanning lines are sequentially selected in units of 1H from the row scanning line g1 to the row scanning line gm by the row scanning signal from the vertical shift register 14. Therefore, the plurality of pixels 12 (12A) constituting the image display unit 11 write data in units of n pixels in one row commonly connected to the selected row scanning line.
Then, after all the pixels 12 (12A) constituting the image display unit 11 have been written, all the pixels are read simultaneously based on the trigger pulse.

FIG. 5A schematically shows a writing period and a reading period of one pixel of 1-bit subframe data output from the horizontal driver 16 to the column data lines d (d1 to dn). A slanting line on the left indicates the writing period. In FIG. 5A, B0b, B1b, and B2b indicate inverted data of the bits BO, B1, and B2. FIG. 5B shows a trigger pulse output from the timing generator 13 to the normal trigger pulse trigger line trig. This trigger pulse is output every subframe. The inversion trigger pulse output to the inversion trigger pulse trigger line trigb is always an inverse logic value with respect to the normal rotation trigger pulse, and is not shown.

First, when the pixel 12A is selected by the row scanning signal, the switch SW11 is turned on,
At that time, the normal subframe data of bit B0 of FIG. 5A output to the column data line d is sampled by the switch SW11 and written to the SM 121 of the pixel 12A. Hereinafter, similarly, subframe data of bit B0 is written to the SM 121 of all the pixels 12A constituting the image display unit 11, and at the time T1 shown in FIG. As shown in (B), a normal rotation trigger pulse of “H” level is simultaneously supplied to all the pixels 12 A constituting the image display unit 11.

As a result, the switches SW12 of all the pixels 12A are turned on, so that the normal subframe data of the bit B0 stored in the SM 121 passes through the switch SW12 to DM1.
In addition to being simultaneously transferred to and held by the capacitor C <b> 1 constituting 22, it is applied to the reflective electrode PE. The holding period of normal subframe data of bit B0 by this capacitor C1 is one sub period from time T1 to time T2 when the next "H" level normal rotation trigger pulse is input as shown in FIG. 5B. It is a frame period. FIG. 5C schematically shows bits of subframe data applied to the reflective electrode PE.

Here, when the bit value of the subframe data is “1”, that is, “H” level, the power supply voltage VDD (3.3 V here) is applied to the reflective electrode PE, and the bit value is “0”, that is, “L”. At the “level”, 0V is applied to the reflective electrode PE. On the other hand, a free voltage can be applied to the common electrode CE of the liquid crystal display element LC as the common electrode voltage Vcom without being limited to GND or VDD. The voltage is switched to the specified voltage at the same time as the input. Here, the common electrode voltage Vcom is set to a voltage lower than 0V by the threshold voltage Vtt of the liquid crystal as shown in FIG. 5D during the subframe period in which the normal rotation subframe data is applied to the reflective electrode PE. The

The liquid crystal display element LC performs gradation display according to the applied voltage of the liquid crystal LCM, which is the absolute value of the difference voltage between the applied voltage of the reflective electrode PE and the common electrode voltage Vcom. Accordingly, in one subframe period from time T1 to time T2 when the normal rotation subframe data of bit B0 is applied to the reflective electrode PE,
As shown in FIG. 5E, the voltage applied to the liquid crystal LCM is such that the bit value of the subframe data is “
When it is “1”, it becomes 3.3 V + Vtt (= 3.3 V − (− Vtt)), and when the bit value of the subframe data is “0”, it becomes + Vtt (= 0 V − (− Vtt)).

FIG. 6 shows the relationship between the applied voltage (RMS voltage) of the liquid crystal and the gray scale value of the liquid crystal. As shown in FIG. 6, in the gray scale value curve, the black gray scale value corresponds to the RMS voltage of the threshold voltage Vtt of the liquid crystal, and the white gray scale value represents the saturation voltage Vsat (= 3.3 V + Vtt) of the liquid crystal.
Shifted to correspond to the current RMS voltage. It is possible to match the gray scale value to the effective part of the liquid crystal response curve. Accordingly, the liquid crystal display element LC is the liquid crystal LCM as described above.
When the applied voltage is (3.3V + Vtt), white is displayed, and when it is + Vtt, black is displayed.

Subsequently, within the subframe period in which the normal subframe data of bit B0 is displayed, the inverted subframe data of bit B0 is written to the SM 121 in the pixel 12A as indicated by B0b in FIG. Are started in order. Then, the inverted subframe data of bit B0 is written to the SM 121 of all the pixels 12A of the image display unit 11, and at time T2 after the completion of the writing, as shown in FIG. Are simultaneously supplied to all the pixels 12 </ b> A constituting the image display unit 11.

As a result, the switches SW12 of all the pixels 12A are turned on, so that the inverted subframe data of the bit B0 stored in the SM 121 passes through the switch SW12 to DM1.
In addition to being transferred to and held by the capacitor C <b> 1 that constitutes 22, it is applied to the reflective electrode PE. The holding period of the inverted subframe data of bit B0 by the capacitor C1 is from time T2 to FIG.
As shown in (B), 1 until time T3 when the next "H" level normal rotation trigger pulse is input.
It is a subframe period. Here, since the inverted subframe data of bit B0 is always in an inverse logical value relationship with the normal subframe data of bit B0, when the normal subframe data of bit B0 is “1”, “0” When the normal rotation subframe data of B0 is “0”, it is “1”.

On the other hand, the common electrode voltage Vcom is set to a voltage higher than the 3.3V threshold voltage Vtt during the subframe period in which the inverted subframe data is applied to the reflective electrode PE, as shown in FIG. The Therefore, in one subframe period from time T2 to time T3 when the inverted subframe data of bit B0 is applied to the reflective electrode PE, the applied voltage of the liquid crystal LCM is −Vtt when the bit value of the subframe data is “1”. (= 3.3V- (3.3V + Vtt))
When the bit value of the subframe data is “0”, −3.3V−Vtt (= 0V− (3.3V +
Vtt)).

Accordingly, when the bit value of the normal subframe data of bit B0 is “1”, the bit value of the inverted subframe data of bit B0 that is subsequently input is “0”, so the liquid crystal L
The applied voltage of CM is − (3.3V + Vtt), and the direction of the potential applied to the liquid crystal LCM is opposite to that in the normal subframe data of the bit B0, but the absolute value is the same. Displays the same white color as when normal subframe data of bit B0 is displayed. Similarly, when the bit value of the normal subframe data of bit B0 is “0”, the bit value of the inverted subframe data of bit B0 that is subsequently input is “1”. The voltage is −Vtt, and the direction of the potential applied to the liquid crystal LCM is opposite to that of the normal rotation subframe data of the bit B0, but the absolute value is the same, so the pixel 12A displays black.

Accordingly, as shown in FIG. 5E, the pixel 12A displays the same gradation in the bit B0 and the complementary bit B0b of the bit B0 and also displays the liquid crystal LCM in the two subframe periods from the time T1 to the time T3. The liquid crystal LC is driven by alternating current driving in which the potential direction is inverted every subframe.
M burn-in can be prevented.

Subsequently, within the subframe period in which the inverted subframe data of the complementary bit B0b is displayed, as indicated by B1 in FIG. 5A, the normal subframe data of the bit B1 is transferred to the SM 121 of the pixel 12A. Writing starts in sequence. Then, normal rotation subframe data of bit B1 is written in the SM 121 of all the pixels 12A of the image display unit 11, and at time T3 after the completion of the writing, as shown in FIG. A pulse is simultaneously supplied to all the pixels 12 </ b> A constituting the image display unit 11.

As a result, the switches SW12 of all the pixels 12A are turned on, so that the normal subframe data of the bit B1 stored in the SM 121 passes through the switch SW12 to DM1.
In addition to being transferred to and held by the capacitor C <b> 1 that constitutes 22, it is applied to the reflective electrode PE. The holding period of the normal subframe data of bit B1 by the capacitor C1 is from time T3 to FIG.
As shown in (B), 1 until time T4 when the next "H" level forward trigger pulse is input.
It is a subframe period.

On the other hand, the common electrode voltage Vcom is set to a voltage lower than 0V by the threshold voltage Vtt of the liquid crystal as shown in FIG. 5D during the subframe period in which the normal rotation subframe data is applied to the reflective electrode PE. . Accordingly, in one subframe period from time T3 to time T4 when the normal rotation subframe data of bit B1 is applied to the reflective electrode PE, the applied voltage of the liquid crystal LCM is as shown in FIG. When the bit value is “1”, 3.3V + Vtt (= 3.3V−
(−Vtt)), and when the bit value of the subframe data is “0”, + Vtt (= 0V−
(-Vtt)).

Subsequently, in the subframe period in which the normal subframe data of the bit B1 is displayed, the inverted subframe data of the bit B1 is written to the SM 121 in the pixel 12A as indicated by B1b in FIG. Are started in order. Then, the inverted subframe data of bit B1 is written to the SM 121 of all the pixels 12A of the image display unit 11, and at time T4 after the completion of the writing, as shown in FIG. Are simultaneously supplied to all the pixels 12 </ b> A constituting the image display unit 11.

As a result, the switches SW12 of all the pixels 12A are turned on, so that the inverted subframe data of the bit B1 stored in the SM 121 passes through the switch SW12 to DM1.
In addition to being transferred to and held by the capacitor C <b> 1 that constitutes 22, it is applied to the reflective electrode PE. The holding period of the inverted subframe data of bit B0 by the capacitor C1 is from time T4 to FIG.
As shown in (B), 1 until time T5 when the next "H" level normal rotation trigger pulse is input.
It is a subframe period. Here, the inverted subframe data of bit B1 is always in the relationship of the inverse logical value with the normal subframe data of bit B1.

On the other hand, the common electrode voltage Vcom is set to a voltage higher than the 3.3V threshold voltage Vtt during the subframe period in which the inverted subframe data is applied to the reflective electrode PE, as shown in FIG. The Therefore, in one subframe period from time T4 to T5 when the inverted subframe data of bit B1 is applied to the reflective electrode PE, the applied voltage of the liquid crystal LCM is −Vtt when the bit value of the subframe data is “1”. (= 3.3V- (3.3V + Vtt))
When the bit value of the subframe data is “0”, −3.3V−Vtt (= 0V− (3.3V +
Vtt)).

Accordingly, as shown in FIG. 5E, the pixel 12A displays the same gradation in the bit B1 and the complementary bit B1b of the bit B1 during the two subframe periods from the time T3 to the time T5, and the liquid crystal LCM Since AC driving is performed in which the potential direction is reversed every subframe, the liquid crystal L
The burn-in of CM can be prevented. Thereafter, the same operation as described above is repeated, and according to the liquid crystal display device having the pixel 12A of the present embodiment, gradation display can be performed by combining a plurality of subframes.

The display periods of bit B0 and complementary bit B0b are the same first subframe period, and the display periods of bit B1 and complementary bit B1b are also the same second subframe period. The subframe period and the second subframe period are not necessarily the same. Here, as an example, the second subframe period is set to be twice the first subframe period. As shown in FIG. 5E, the third subframe period, which is the display period of the bit B2 and the complementary bit B2b, is set to be twice the second subframe period.
The same applies to the other subframe periods. The length of each subframe period is determined to be a predetermined length according to the system, and the number of subframes is also determined to be an arbitrary number.

  Next, another embodiment of the main pixel of the present invention will be described.

In the pixel 12A of the first embodiment, the SM12 is configured by the SRAM 201 as first signal holding means for sampling and storing the subframe data supplied via the column data line d.
1 and the second signal holding means for holding the sub-frame data supplied from the first signal holding means for a predetermined period and applying it to the reflective electrode is the DM 122 constituted by the DRAM 202, thereby reducing the size of the pixel. It was realized. On the other hand, in the second and third embodiments of the pixel described below, the first and second signal holding means are both S, as in the pixel described in Patent Document 1.
It is a RAM. However, in the second and third embodiments of the main pixel of the present invention, the operation is stabilized as compared with the pixel described in Patent Document 1 by configuring the SRAM in a predetermined configuration.

FIG. 7 shows a circuit diagram of a second embodiment of a pixel which is a main part of the liquid crystal display device according to the present invention. In the figure, the same components as those in FIG. In FIG. 7, the pixel 12B of the second embodiment is inverted with respect to the normal data column data line dj extending in the column direction (Y direction) with one end connected to the level shifter / pixel driver 163 in FIG. Vertical shift with any one set of normal data column data line d and inverted data column data line db out of a total of n column data lines, the data column data line dbj as a set A first static random access memory (SRAM) is a pixel provided at an intersection with one arbitrary row scanning line g that is connected to the register 14 at one end and extends in the row direction (X direction). ) 211, a second static random access memory (SRAM) 212, and a liquid crystal display element L
And C. The first SRAM 211 includes switches SW21a and SW21b that constitute first and second switching means, and first signal holding means (SM) 123. The second SRAM 212 includes switches SW22a and SW22b constituting third and fourth switching means, and second signal holding means (SM) 124.

The switch SW21a includes an NMOS transistor having a gate connected to the row scanning line g, a drain connected to the column data line d, and a source connected to one input terminal of the SM123. The switch SW21b has a gate connected to the row scanning line g, a drain connected to the column data line db, and a source connected to the other input terminal of the SM123.
It is composed of MOS transistors.

SM123 has two inverters INV with one output terminal connected to the other input terminal.
21 and a self-holding memory composed of INV22. The input terminal of the inverter INV21 is connected to the output terminal of the inverter INV22, the source of the NMOS transistor constituting the SW21a, and the switch SW22a. The input terminal of the inverter INV22 is connected to the output terminal of the inverter INV21, the source of the NMOS transistor constituting the SW21b, and the switch SW22b. Inverters INV21 and INV22
These are all known CMOS inverter configurations as shown in FIG.

The switch SW22a has a gate connected to the trigger line trig and a drain connected to SM12.
3 is connected to a connection point between the switch SW21a and an NMOS transistor whose source is connected to one input terminal of the SM124. The switch SW22b is configured by an NMOS transistor having a gate connected to the trigger line trig, a drain connected to a connection point between the SM123 and the switch SW21b, and a source connected to the other input terminal of the SM124.

The SM 124 is a self-holding memory composed of two inverters INV23 and INV24 having one output terminal connected to the other input terminal. The inverter INV23 is
Its input terminal is connected to the output terminal of the inverter INV24, the source of the NMOS transistor constituting the SW 22a, and the reflective electrode PE. The input terminal of the inverter INV24 is connected to the output terminal of the inverter INV23 and the source of the NMOS transistor that constitutes the SW 22b. Inverters INV23 and INV24 are connected to inverter INV
Similar to 21 and INV22, both are known CMOS inverter configurations as shown in FIG.

The pixel 12B in this embodiment performs an operation similar to the operation described with the timing chart of FIG. When the pixel 12B is selected by the row scanning signal, the switches SW21a and SW21a
21b is turned on. The switches SW21a and SW21b are supplied with 1-bit normal subframe data and 1-bit inverted subframe data having opposite logical values through the column data line d and the column data line db. Here, the switches SW21a and SW21b are N
It is composed of MOS transistors, and when normal subframe data and inverted subframe data are VDD side voltage ("H"), it is not input by the threshold voltage Vth of the NMOS transistor, but only a voltage lower than VDD by Vth is input. Not. Moreover, almost no current flows at this voltage. Therefore, normal subframe data or inverted subframe data at the GND potential (“L”) sampled by the switch SW21a or SW21b is written to the SM123.

Data writing to the SM 124 is performed by the switches SW22a and SW22b controlled by the trigger pulse supplied via the trigger line trig. Data supplied to the switch SW22a from the connection point of the SM123 and the switch SW21a via the wiring m, and S
Data supplied to the switch SW22b from the connection point between the M123 and the switch SW21b via the wiring mb is in an inverse logical value relationship. Switches SW22a and SW22b
Is composed of NMOS transistors, and the VDD side voltage ("H" level) is NMO.
Only a voltage lower than VDD by Vth is input without being input by Vth of the S transistor. Moreover, since this voltage is driven in the vicinity of Vth of the NMOS transistor, almost no current flows. For this reason, the data of the wiring m or the wiring mb at the GND potential (“L” level) is written in the SM 124.

Here, immediately after the sub-frame data is written in the SM 123 of all the pixels 12B constituting the image display unit 11, when the “H” level trigger pulse is input via the trigger line trig, the data of the SM 124 is stored. It is necessary to rewrite the data stored in SM123. That is, the data stored in the SM 124 must not be rewritten with the data stored in the SM 123.
For this reason, it is necessary to make the driving force of the inverter constituting SM124 smaller than the driving force of the inverter constituting SM123. That is, when the stored data of SM123 and SM124 are different, the inverter INV2 is input when the “H” level trigger pulse is input.
1 so that the output data of the inverter INV23 collides, and the output data of the inverter INV21 reliably rewrites the data of the inverter INV24.
The driving force of the inverter INV21 needs to be larger than the driving force of the inverter INV23. Further, in the relationship between the inverter INV22 and the inverter INV24, the inverter IV
The driving force of the inverter INV22 needs to be larger than the driving force of the inverter INV24 so that the output data of the NV22 surely rewrites the data of the inverter INV23.

This will be further described with reference to FIG. Inverter INV21 and inverter IN
To briefly explain the relationship of V23, when the output data of SM123 in the wiring mb is at "H" level, the PMOS transistor PTr21 constituting the inverter INV21 is turned on. On the other hand, when the output data on the wiring mb side of the SM 124 is already at the “L” level, the NMOS transistor NTr23 constituting the inverter INV23 is on.

At this time, the switch SW22b is triggered by the “H” level trigger pulse of the trigger pulse line trig.
Is turned on, and inverters INV21 and INV2 are turned on.
When the outputs of 3 are conductive, the current is the PMOS transistor PT of the inverter INV21
From VDD to GN through r21 and NMOS transistor NTr23 of inverter INV23
D flows. At this time, the voltage of the wiring mb is determined by the ratio of the on resistance of the PMOS transistor PTr21 and the NMOS transistor NTr23.

On the other hand, if the output data of the SM 123 in the wiring mb is “L” level and the output data on the wiring mb side of the SM 124 is already “H” level, the N constituting the switch SW22b
The MOS transistor is turned on by the “H” level trigger pulse on the trigger pulse line trig,
When the outputs of the inverters INV21 and INV23 become conductive, current flows from VDD to GND through the PMOS transistor PTr23 of the inverter INV23 and the NMOS transistor NTr21 of the inverter INV21. At this time, the voltage of the wiring mb is P
It is determined by the ratio of the on resistance of the MOS transistor PTr23 and the NMOS transistor NTr21.

In addition, an input gate of an inverter INV24 (not shown) is connected to the wiring mb.
The output data of the inverter INV24 is determined to be “L” level or “H” level by the input of the voltage level of the wiring mb. That is, since the output data of SM124 is determined by the voltage level of the wiring mb, in order to rewrite the data of SM124 with the output data of SM123, the ON resistances of the transistors of inverters INV21 and INV22 are the transistors of inverters INV23 and INV24. It must be lower than the on-resistance. Due to the low on-resistance of the transistors of the inverters INV21 and INV22, the output data of SM123 is reliably S regardless of the data level of SM124.
The data of M124 can be rewritten.

The use of a transistor with low on-resistance can be realized by using a transistor with high driving power, and can be realized by reducing the gate length or increasing the gate width.

When 1-bit data stored in SM123 is written to SM124 of all the pixels 12B all at once, the trigger pulse of the trigger pulse line trig becomes “L” level, and the switch SW
Each of 22a and SW22b is turned off. Therefore, the SM 124 can hold the written 1-bit data, and can fix the potential of the reflective electrode PE to a potential corresponding to the held data for an arbitrary time (here, one subframe period).

The data written in the SM 124 is the normal rotation data and the inverted data that are switched every subframe shown in FIG. 5C, while the common electrode potential Vcom is also the above-mentioned data as shown in FIG. Since the voltage is alternately switched to a predetermined potential every subframe in synchronization with writing, according to the liquid crystal display device using the pixel 12B of the present embodiment, the pixel 12A of the first embodiment.
Similarly to the liquid crystal display device using the liquid crystal display, alternating current driving that is reversed every subframe is performed, so that it is possible to perform display while preventing the liquid crystal LCM from being burned. Further, the pixel 12 of the present embodiment.
According to the liquid crystal display device using B, inverters INV21 and INV constituting SM123
Since the driving power of each of the inverters INV23 and INV24 constituting the SM22 and the driving power of each transistor constituting the switches SW21a, SW21b, SW22a and SW22b is set in a predetermined relationship, stable and accurate gradation Can be displayed.

Note that the switches SW21a, 21b, 22a, and 22b may be configured by PMOS transistors, and in that case, the polarity may be considered as being opposite to the above description, and the details are omitted.

Next, a description will be given of a third embodiment of the main pixel of the liquid crystal display device according to the present invention.
FIG. 9 shows a circuit diagram of a third embodiment of a pixel which is a main part of the liquid crystal display device according to the present invention. In the figure, the same components as those in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted.

In FIG. 9, the pixel 12C of the third embodiment includes one of the column data lines d1 to dn that are connected to the level shifter / pixel driver 163 in FIG. 1 and extend in the column direction (Y direction).
Pixels provided at intersections between any one column data line d and any one row scanning line g that has one end connected to the vertical shift register 14 and extends in the row direction (X direction). The first static random access memory (SRAM) 213, the second static random access memory (SRAM) 214, and the liquid crystal display element LC.
The first SRAM 213 includes a switch SW31 constituting the first switching means, and a first
Signal holding means (SM) 125. In addition, the second SRAM 214 has the second
The switch SW32 constituting the switching means and the second signal holding means (SM) 126
It is composed of. The pixel 12C of the present embodiment is composed of two SRAM stages as in the pixel 12B, but is characterized in that writing to the SM 125 in the SRAM 213 and the SM 126 in the SRAM 214 is performed by one switch SW31 and SW32, respectively. .

The switch SW31 includes an NMOS transistor having a gate connected to the row scanning line g, a drain connected to the column data line d, and a source connected to one input terminal of the SM 125. The SM 125 is a self-holding memory including two inverters INV31 and INV32 having one output terminal connected to the other input terminal. Inverter IN
V31 is an NMO whose input terminal constitutes the output terminal of the inverter INV32 and SW31.
It is connected to the source of the S transistor. The input terminal of the inverter INV32 is connected to the output terminal of the inverter INV31 and the drain of the NMOS transistor constituting the SW32. The inverters INV31 and INV32 each have a known CMOS inverter configuration as shown in FIG.

The switch SW32 has a gate connected to the trigger line trig and a drain connected to SM125.
And an NMOS transistor having a source connected to the input terminal of SM126. The SM 126 is a self-holding memory composed of two inverters INV33 and INV34 having one output terminal connected to the other input terminal. The inverter INV33 has an input terminal connected to the output terminal of the inverter INV34 and the reflective electrode PE. The inverter INV34 has an input terminal connected to the inverter INV3.
3 and the source of an NMOS transistor constituting the SW 32.
Each of the inverters INV33 and INV34 has a known CMOS inverter configuration as shown in FIG. 3 like the inverters INV31 and INV32.

The pixel 12C in this embodiment performs an operation similar to the operation described with the timing chart of FIG. When the pixel 12C is selected by the row scanning signal, the switch SW31 is turned on, and the normal subframe data output to the column data line d at that time is sampled by the switch SW31 and written to the SM 125 of the pixel 12C. Thereafter, in the same manner, normal subframe data is written to the SMs 125 of all the pixels 12C constituting the image display unit 11, and after the writing operation is completed, an “H” level trigger pulse is sent to the image display unit 11. Are simultaneously supplied to all the pixels 12C constituting the. As a result, the switches SW32 of all the pixels 12C are turned on, so that the normal subframe data stored in the SM125 is transferred to the DRAM 126 through the switch SW32 and held at the same time.
Applied to the reflective electrode PE. The retention period of the normal rotation subframe data of SM126 is “
This is one subframe period until the trigger pulse of “H” is input to the trigger line trig.

Subsequently, each pixel 12C in the pixel display unit 11 is selected in units of rows by the row scanning signal in the same manner as described above, and the previous normal subframe data and the inverted subframe data having the opposite logical value are obtained for each pixel. It is written in SM125. SM of all pixels 12C constituting the image display unit 11
When the writing of the inverted subframe data to 125 is completed, the “H” level trigger pulse is simultaneously supplied to all the pixels 12 </ b> C constituting the image display unit 11. As a result, the switches SW32 of all the pixels 12C are turned on, so that the inverted subframe data stored in the SM125 is transferred and held all at once to the DRAM 126 through the switch SW32 and applied to the reflective electrode PE. . The inversion subframe data holding period of SM 126 is one subframe period until the next “H” trigger pulse is input to the trigger line trig.

Data writing to the SM 125 is performed by input from one switch SW31 as described above. In this case, the driving power of the transistor in the input-side inverter INV31 constituting the SM 125 as viewed from the switch SW31 is higher than that of the transistor in the output-side inverter INV32 constituting the SM 125 as viewed from the switch SW31. A large transistor is used. Further, the driving power of the NMOS transistor that constitutes the switch SW31 is a transistor that is larger than the driving power of the NMOS transistor that constitutes the inverter INV32. This is because the inverter INV12 of the pixel 12A described above.
1 and the driving force relationship between the INV 122 and the switch SW11 is the same, and the description thereof is omitted.

Further, data writing to the SM 126 is performed through one switch SW32. In this case, the input-side inverter INV constituting the SM 126 as viewed from the switch SW32
The transistor in 33 is a transistor with a large driving force, and the transistor in the inverter INV 34 on the output side constituting the SM 126 when viewed from the switch SW32 is a transistor with a small driving force.

By doing this, when the trigger pulse becomes “H” level and the switch SW32 is turned on, if the stored data of SM125 and SM126 are different, inverter IN
Although the output data of V31 and the output data of inverter INV34 collide, since the driving force of inverter INV31 is larger than the driving force of inverter INV34, SM1
The data of SM126 is changed to SM1 without the data of 25 being rewritten to the data of SM126.
It can be rewritten to 25 data.

Further, the driving power of the NMOS transistor constituting the switch SW32 is configured by a transistor larger than the driving power of the NMOS transistor constituting the inverter INV34. This is because when the SM126 data is rewritten, particularly when the input voltage b on the switch SW32 side of the SM126 is “L” level and the SM125 data is “H” level, the voltage b is higher than the threshold voltage at which the inverter INV33 is inverted. This is because it is necessary to increase the height.

That is, the voltage b is determined by the ratio between the current of the NMOS transistor that constitutes the inverter INV34 and the current of the switch SW32. At this time, since the switch SW32 is an NMOS transistor, the voltage on the VDD side is not input by the threshold value Vth of the NMOS transistor, and the “H” level voltage is lower than VDD by Vth. Moreover, at this voltage, N
Since the MOS transistor is driven near Vth, almost no current flows. That is, the higher the voltage b that conducts the input switch SW32, the smaller the current that flows through the switch SW32. That is, the input side inverter INV33 whose voltage b is SM126 is “H”.
In order to reach the threshold voltage or higher which inverts to the level, the current flowing through the switch SW32 needs to be larger than the current flowing through the NMOS transistor constituting the inverter INV34. Considering this driving force ratio, the transistor size of the switch SW32 and the inverter I
It is necessary to determine the transistor size of the NMOS transistor that constitutes the NV 34.

When 1-bit data stored in SM125 is written to SM126 of all the pixels 12C all at once, the trigger pulse of the trigger pulse line trig becomes “L” level, and the switch SW
23 is turned off. Therefore, the SM 126 holds the written 1-bit data, and can fix the potential of the reflective electrode PE to a potential corresponding to the held data for an arbitrary time (here, one subframe period).

The data written in the SM 126 is the normal data and the inverted data that are switched every subframe shown in FIG. 5C, while the common electrode potential Vcom is also the above-mentioned data as shown in FIG. Since the potential is alternately switched to a predetermined potential every subframe in synchronization with writing, according to the liquid crystal display device using the pixel 12C of the present embodiment, the pixel 12 of each of the above embodiments.
Similarly to the liquid crystal display device using A or 12B, alternating current driving that is reversed for each subframe is performed, so that it is possible to perform display while preventing the liquid crystal LCM from being burned. Furthermore, according to the liquid crystal display device using the pixel 12C of the present embodiment, the inverter INV constituting the SM 125
31 and INV32, the driving forces of the inverters INV33 and INV34 constituting the SM 126, and the driving forces of the transistors constituting the switches SW31 and SW32 are set in a predetermined relationship, so that stable and accurate gradation display can be performed. .

Note that the switches SW31 and SW32 may be constituted by PMOS transistors, and in that case, it is only necessary to consider the polarity opposite to that described above, and thus the details are omitted.

The present invention is not limited to the above embodiment. For example, the pixel electrode has been described as the reflective electrode PE, but may be a transmissive electrode.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 11 Image display part 12, 12A, 12B, 12C Pixel 13 Timing generator 14 Vertical shift register 15 Data latch circuit 16 Horizontal driver 112 Electrode 121, 123, 125 for capacity | capacitance C1 1st signal holding means (SM)
122 Second signal holding means (DM)
124, 126 Second signal holding means (SM)
201, 211-214 Static random access memory (SRAM)
202 Dynamic Random Access Memory (DRAM)
161 Horizontal shift register 162 Latch circuit 163 Level shifter / pixel driver d1 to dn column data line g1 to gm row scanning line
trig trigger line
trigb Inversion trigger pulse trigger line LC Liquid crystal display element LCM Liquid crystal PE Reflective electrode CE Common electrode C1 Capacitance INV11, INV12, INV21, INV22, INV31, INV32 Inverter Tr1, NTr, NTr12, NTr21, NTr23 N-channel MOS transistor (
NMOS transistor)
Tr2, PTr, PTr11, PTr21, PTr23 P-channel MOS transistor (
PMOS transistor)

Claims (2)

Each of a plurality of pixels provided at an intersection where a plurality of sets of column data lines and a plurality of row scanning lines intersect each other, each having two column data lines as a set,
A display element in which liquid crystal is filled and sealed between the opposing pixel electrode and the common electrode;
Normal subframe data for displaying each frame of the video signal in a plurality of subframes having a display period shorter than one frame period of the video signal is displayed in one column of the two column data lines. First switching means for sampling via a data line;
Second switching means for sampling inversion subframe data having an inverse logical value relationship with the normal rotation subframe data via the other column data line of the set of the two column data lines;
From the first and second inverters that store the normal subframe data and the inverted subframe data sampled by the first and second switching means, respectively, and whose output terminals are connected to the other input terminal First signal holding means constituting a first static random access memory together with the first and second switching means,
Third switching means for outputting the normal rotation subframe data from a connection point between the first signal holding means and the first switching means;
Fourth switching means for outputting the inverted subframe data from a connection point between the first signal holding means and the second switching means;
The stored contents are rewritten with the normal subframe data and the inverted subframe data stored in the first signal holding means supplied through the third and fourth switching means, and the output data is applied to the pixel electrode. A second static random access memory which comprises a third and a fourth inverter whose output terminals are connected to the other input terminal, together with the third and fourth switching means. Signal holding means,
Of the first and second inverters, the driving force of the second inverter whose output terminal is connected to the first switching means is the first driving force whose output terminal is connected to the second switching means. The driving force of the first and second inverters is set smaller than the driving force of the inverter, and the driving force of the third and fourth inverters is set larger than the driving force of the inverters,
Of the plurality of pixels constituting the image display unit, all of the plurality of pixels are repeatedly written by writing the normal subframe data and the inverted subframe data to the first signal holding unit for each pixel in a row unit. , The normal and inverted subframe data stored in the first signal holding means are turned on by turning on the third and fourth switching means of all the plurality of pixels by a trigger pulse. The second of the plurality of pixels by
A liquid crystal display device comprising pixel control means for performing an operation of rewriting the stored contents of the signal holding means for each subframe. Each of a plurality of pixels provided at an intersection where a plurality of column data lines and a plurality of row scanning lines intersect with each other,
A display element in which liquid crystal is filled and sealed between the opposing pixel electrode and the common electrode;
Each sub-frame data for displaying each frame of the video signal in a plurality of sub-frames having a display period shorter than one frame period of the video signal is composed of one transistor for sampling through the column data line. First switching means;
The subframe data sampled by the first switching means is stored in the first and second inverters whose output terminals are connected to the other input terminal. First signal holding means constituting the static random access memory of
Second switching means comprising one transistor for outputting the subframe data stored in the first signal holding means;
The stored contents are rewritten with the sub-frame data stored in the first signal holding means supplied through the second switching means, and the output data is applied to the pixel electrode. Consisting of third and fourth inverters connected to the terminals,
A second signal holding means which constitutes a second static random access memory together with the second switching means,
Of the first and second inverters, the driving power of the second inverter whose output terminal is connected to the first switching means is set to be smaller than the driving power of the first inverter, and Driving power of the fourth inverter, which is set smaller than the driving power of the transistors constituting the first switching means, and whose output terminal is connected to the second switching means among the third and fourth inverters. Is set to be smaller than the driving force of the third inverter and set to be smaller than the driving force of the transistors constituting the second switching means, and the driving force of the first inverter is It is set to be larger than the driving force of the fourth inverter,
After writing the sub-frame data to the first signal holding unit for each pixel in the row unit among the plurality of pixels constituting the image display unit, the trigger pulse is written. To turn on the second switching means for all of the plurality of pixels, and store the contents stored in the second signal holding means of the plurality of pixels by the subframe data stored in the first signal holding means. A liquid crystal display device comprising pixel control means for performing a rewriting operation for each subframe.

Images