JP4288849B2 - Active matrix display device and portable terminal using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device and a portable terminal using the active matrix display device, and more particularly to an active matrix display device including a drive system including a reference voltage selection type DA (digital-analog) conversion circuit and the display device. The present invention relates to a portable terminal used as a part.
[0002]
[Prior art]
In recent years, mobile terminals such as mobile phones and PDAs (Personal Digital Assistants) have become widespread. One of the factors of the rapid spread of these portable terminals is a liquid crystal display device mounted as an output display unit. This is because the liquid crystal display device has a characteristic that does not require power for driving in principle and is a display device with low power consumption.
[0003]
In this liquid crystal display device or the like, the digital interface drive circuit tends to be integrally formed on the same substrate as the display area portion. In this drive circuit integrated liquid crystal display device, a display area portion in which a large number of pixels using polysilicon TFTs (Thin Film Transistors) as switching elements are arranged in a matrix form in a peripheral portion (frame). A horizontal drive system and a vertical drive system are arranged, and these drive systems are integrally formed on the same substrate together with the display area portion using TFTs.
[0004]
By the way, in the digital interface driving circuit, a DA conversion circuit for converting input digital data into an analog signal is used. As this DA conversion circuit, for example, a reference voltage selection type DA conversion circuit that selects a reference voltage corresponding to digital image data from a plurality of reference voltages and outputs the selected reference voltage as an analog image signal is known. This reference voltage selection type DA converter circuit requires a reference voltage generation circuit that generates a plurality of reference voltages. Conventionally, this reference voltage generating circuit is formed on a single crystal silicon substrate which is a substrate different from the substrate on which the display area portion is formed.
[0005]
[Problems to be solved by the invention]
As described above, in a display device typified by a liquid crystal display device, a reference voltage generation circuit that generates a plurality of reference voltages is formed on a substrate different from the substrate on which the display area portion is formed. As the number of parts that make up the device increases, it must be created in a separate process, which hinders the downsizing and cost reduction of the set.
[0006]
The present invention has been made in view of the above problems, and an object thereof is to provide an active matrix display device capable of reducing the size and cost of a set, and a portable terminal using the active matrix display device as a display unit There is to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a display area portion in which pixels having electro-optic elements are arranged in a matrix, a reference voltage generating circuit for generating a plurality of reference voltages, and a plurality of reference voltages. A horizontal drive having a reference voltage selection type DA converter circuit for selecting a reference voltage corresponding to digital data from the inside, and supplying the reference voltage selected by the DA converter circuit as an image signal to each pixel of the selected pixel row In the active matrix display device including the circuit, a pair of horizontal drive circuits are arranged above and below the display area portion, and the reference voltage generation circuit is provided on the same substrate together with the display area portion and the horizontal drive circuit. together is created, a pair of water at opposite sides across the pixel array portion a vertical driving circuit for selecting pixels in units of rows of the display area unit Disposed one equidistant from the drive circuit, adopts a direct supply configuration without interposing a buffer circuit with respect to a plurality of reference voltages pair of horizontal drive circuits. The active matrix display device is used as a display unit of a mobile terminal.
[0008]
In the active matrix display device having the above configuration or a portable terminal using the active matrix display device, the reference voltage generation circuit is formed on the same substrate together with the display area unit and the horizontal drive circuit, thereby reducing the number of components constituting the set. it can. Therefore, it is possible to reduce the cost of the set, and to make it thinner and more compact. In addition, since the reference voltage generation circuit is provided at a position equidistant from the pair of horizontal drive circuits, the wiring length between the pair of horizontal drive circuits can be made equal, so that a plurality of reference voltages are supplied to the pair of horizontal drive circuits. On the other hand, it can be directly supplied without interposing a buffer circuit. Thereby, a buffer circuit required when the reference voltage generating circuit is arranged on another substrate can be omitted.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a configuration example of a display device according to the present invention. Here, for example, a case where the present invention is applied to an active matrix liquid crystal display device using a liquid crystal cell as an electro-optical element of each pixel will be described as an example.
[0010]
In FIG. 1, on a transparent insulating substrate, for example, a glass substrate 11, a display area portion 12 in which a large number of pixels including liquid crystal cells are arranged in a matrix, a pair of upper and lower H drivers (horizontal drive circuits) 13U, 13D and V A reference voltage generation circuit 15 that generates a plurality of reference voltages is integrated together with a driver (vertical drive circuit) 14. The glass substrate 11 includes a first substrate on which a large number of pixel circuits including active elements (for example, transistors) are arranged and formed in a matrix, and a second substrate that is arranged to face the first substrate with a predetermined gap. And the substrate. A liquid crystal is sealed between the first and second substrates.
[0011]
FIG. 2 shows an example of a specific configuration of the display area unit 12. Here, for simplification of the drawing, the case of a pixel array of 3 rows (n−1 rows to n + 1 rows) and 4 columns (m−2 columns to m + 1 columns) is shown as an example. 2, vertical scanning lines..., 21n-1, 21n, 21n + 1,... And data lines..., 22m-2, 22m-1, 22m, 22m + 1,. The unit pixels 23 are arranged at the intersections.
[0012]
The unit pixel 23 includes a thin film transistor TFT, which is a pixel transistor, a liquid crystal cell LC, and a storage capacitor Cs. Here, the liquid crystal cell LC means a capacitance generated between a pixel electrode (one electrode) formed by a thin film transistor TFT and a counter electrode (the other electrode) formed opposite thereto.
[0013]
The thin film transistor TFT has a gate electrode connected to the vertical scanning lines..., 21n-1, 21n, 21n + 1,..., And a source electrode connected to the data lines ..., 22m-2, 22m-1, 22m, 22m + 1,. . In the liquid crystal cell LC, the pixel electrode is connected to the drain electrode of the thin film transistor TFT, and the counter electrode is connected to the common line 24. The storage capacitor Cs is connected between the drain electrode of the thin film transistor TFT and the common line 24. A predetermined DC voltage is applied to the common line 24 as a common voltage Vcom.
[0014]
One end of each of the vertical scanning lines..., 21n-1, 21n, 21n + 1,... Is connected to each output end of the corresponding row of the V driver 14 shown in FIG. The V driver 14 is constituted by, for example, a shift register, and sequentially generates vertical selection pulses in synchronization with a vertical transfer clock VCK (not shown) to give them to the vertical scanning lines..., 21n-1, 21n, 21n + 1,. A vertical scan is performed.
[0015]
On the other hand, in the display area 12, for example, odd-numbered data lines..., 22m-1, 22m + 1,... Are connected to output terminals of corresponding columns of the H driver 13U shown in FIG. .., 22m-2, 22m,... Are connected to output terminals of corresponding columns of the H driver 13D shown in FIG. An example of a specific configuration of the H drivers 13U and 13D is shown in FIG.
[0016]
As shown in FIG. 3, the H driver 13U includes a shift register 25U, a sampling latch circuit (data signal input circuit) 26U, a line sequential latch circuit 27U, and a DA converter circuit 28U. The shift register 25U performs horizontal scanning by sequentially outputting shift pulses from each transfer stage in synchronization with a horizontal transfer clock HCK (not shown). The sampling latch circuit 26U samples and latches the input digital image data of a predetermined bit in a dot sequential manner in response to the shift pulse supplied from the shift register 25U.
[0017]
The line-sequential latch circuit 27U performs line-sequencing by re-latching the digital image data latched dot-sequentially by the sampling latch circuit 26U in units of one line, and outputs the digital image data for one line at a time. . The DA conversion circuit 28U has, for example, a reference voltage selection type circuit configuration, converts the digital image data for one line output from the line-sequential latch circuit 27U into an analog image signal, and the data lines of the pixel area section 12 described above. ..., 22m-2, 22m-1, 22m, 22m + 1,.
[0018]
FIG. 4 shows a configuration example of a unit circuit of the reference voltage selection type DA conversion circuit 28U. Here, the case where the input digital data is, for example, 3 bits (b2, b1, b0) is shown as an example, and 8 (= 2 ³ ) reference voltages V0 to 0 for the 3-bit data. V7 will be prepared. One unit circuit is arranged for each data line..., 22m-2, 22m-1, 22m, 22m + 1,.
[0019]
The lower H driver 13D also includes a shift register 25D, a sampling latch circuit 26D, a line-sequential latch circuit 27D, and a reference voltage selection type DA converter circuit 28D, just like the upper H driver 13U. Yes. In the active matrix liquid crystal display device according to this example, the H drivers 13U and 13D are arranged above and below the display area unit 12. However, the present invention is not limited to this, and only one of the upper and lower sides is arranged. It is also possible to adopt a configuration arranged in
[0020]
As is clear from FIGS. 1 and 3, the reference voltage generation circuit 15 is also integrated on the same glass substrate 11 together with the display area unit 12, as with the H drivers 13 U and 13 D and the V driver 14. Here, for example, in the case of a liquid crystal display device having a configuration in which the H drivers 13U and 13D are arranged above and below the display area unit 12, a frame area (side of the display area unit 12) where the H drivers 13U and 13D are not mounted. It is preferable to mount the reference voltage generation circuit 15 in the peripheral area.
[0021]
This is because the H drivers 13U and 13D have more components than the V driver 14 as described above, and their circuit area is often very large. Therefore, the sides where the H drivers 13U and 13D are not mounted. The reference voltage generating circuit 15 is integrated on the same glass substrate 11 as the display area unit 12 without reducing the effective screen ratio (the area ratio of the effective area unit 12 with respect to the glass substrate 11). Because it can be done.
[0022]
In the active matrix liquid crystal display device according to this example, the V driver 14 is integrated on one side of the frame area on the side where the H drivers 13U and 13D are not mounted. The reference voltage generating circuit 15 is integrated in the frame area.
[0023]
A typical configuration example of the reference voltage generating circuit is shown in FIG. The reference voltage generation circuit according to this configuration example includes two switch circuits 31 and 32 that switch the positive power supply voltage VCC and the negative power supply voltage VSS in a predetermined cycle and in opposite phases, and outputs of the switch circuits 31 and 32. It consists of n + 1 resistors R0 to Rn connected in series between the ends, and by dividing the voltage VCC-VSS by these resistors R0 to Rn, n reference voltages V0 to Vn from the common connection point of each resistor. -1 is derived and output via the buffer circuits 33-1 to 33-n.
[0024]
In the reference voltage generating circuit having the above configuration, the buffer circuits 33-1 to 33-n have an impedance conversion function, and the reference voltage generating circuit is formed on a separate substrate as in the prior art, and the DA on the glass substrate 11 is formed. When the reference voltage is transmitted to the conversion circuit, even if the wiring impedance from the reference voltage generation circuit to the DA conversion circuit is increased to increase the wiring impedance, the upper and lower H drivers (H in FIG. 1) (This corresponds to the drivers 13U and 13D).
[0025]
On the other hand, the active matrix liquid crystal display device according to the present embodiment employs a configuration in which the reference voltage generation circuit 15 is integrated on the same glass substrate 11 together with the H drivers 13U and 13D. The wiring length between the H drivers 13U and 13D can be set extremely short. In particular, as can be seen from FIG. 3, when integrating the reference voltage generation circuit 15, the reference voltage generation circuit 15 is located at a substantially intermediate position in the vertical direction of the display area 12, that is, at an approximately equal distance from the upper and lower H drivers 13U and 13D. By arranging at the position, the wiring length between the H drivers 13U and 13D can be set substantially equal.
[0026]
Thus, in configuring the reference voltage generating circuit 15, as shown in the circuit diagram of FIG. 6, the buffer circuits 33-1 to 33-n used in the general circuit example shown in FIG. . That is, as apparent from the configuration example shown in FIG. 6, n reference voltages V0 to Vn-1 derived from the common connection point of the resistors R0 to Rn can be directly supplied to the upper and lower H drivers 13U and 13D. It becomes like this. As a result, the circuit configuration of the reference voltage generation circuit 15 can be simplified to the extent that the buffer circuits 33-1 to 33-n can be omitted.
[0027]
In FIG. 6, the same parts as those in FIG. In FIG. 6, the switches SW1 to SW4 constituting the switch circuits 31 and 32 are constituted by transistors, for example. FIG. 7 shows waveforms of control pulses φ1, φ2, upper limit, lower limit voltage VA, voltage VB, and reference voltages V0, Vn−1.
[0028]
In the switch circuits 31 and 32, the switches SW1 and SW4 are switched by the control pulse φ1, and the switches SW2 and SW3 are switched by the control pulse φ2 having a phase opposite to that of the control pulse φ1. As described above, the positive power supply voltage VCC and the negative power supply voltage VSS are switched in reverse phases with a constant period, for example, 1H (H is a horizontal scanning period). This is for driving.
[0029]
Further, when integrating the reference voltage generation circuit 15, since the thin film transistor TFT is used as each pixel transistor of the display area unit 12, the thin film transistor is also used as a transistor constituting the switch circuits 31 and 32 of the reference voltage generation circuit 15. At least these transistor circuits are formed on the same glass substrate 11 together with the display area portion 12, so that the manufacture becomes easy and can be realized at low cost.
[0030]
As for thin film transistors, the integration is becoming easier as performance is improved and power consumption is reduced in recent years. Therefore, the manufacturing process can be simplified by integrally forming the reference voltage generation circuit 15, particularly at least the transistor circuit, on the same glass substrate 11 on the same glass substrate 11 using the same thin film transistor as the pixel transistor of the display area portion 12. Therefore, the cost can be reduced, and further, the thickness can be reduced and the size can be reduced due to the integration.
[0031]
In the above embodiment, the case where the present invention is applied to an active matrix liquid crystal display device has been described as an example. However, the present invention is not limited to this, and an electroluminescence (EL) element is used as an electro-optical element of each pixel. The present invention can be similarly applied to other active matrix display devices such as EL display devices.
[0032]
The active matrix type display device represented by the active matrix type liquid crystal display device according to the above embodiment is used as a display for OA equipment such as a personal computer and a word processor, a television receiver, etc. It is suitable for use as a display portion of portable terminals such as mobile phones and PDAs that are being made more compact and compact.
[0033]
FIG. 8 is an external view schematically showing the configuration of a mobile terminal to which the present invention is applied, for example, a mobile phone.
[0034]
The mobile phone according to this example has a configuration in which a speaker unit 42, a display unit 43, an operation unit 44, and a microphone unit 45 are arranged in this order from the upper side on the front side of the device casing 41. In the mobile phone having such a configuration, for example, a liquid crystal display device is used as the display unit 43, and the active matrix liquid crystal display device according to the above-described embodiment is used as the liquid crystal display device.
[0035]
As described above, in the mobile terminal such as a mobile phone, the active matrix liquid crystal display device according to the above-described embodiment is used as the display unit 43, so that the circuit configuration of the reference voltage generation circuit mounted on the liquid crystal display device is simple. Thus, the cost of the display device can be reduced, and further, the thickness and the size can be reduced. Therefore, the cost of the terminal body can be reduced, and the thickness and the size can be reduced.
[0036]
【The invention's effect】
As described above, according to the present invention, in an active matrix display device or a portable terminal using the same as a display unit, the reference voltage generation circuit is formed on the same substrate together with the display area unit and the horizontal drive circuit. As a result, the number of parts constituting the set can be reduced, and the cost of the set can be reduced, and further, the thickness and size can be reduced. In addition, when the reference voltage generation circuit is arranged on a separate substrate by arranging the reference voltage generation circuit at the same distance from the pair of horizontal drive circuits on the opposite side of the vertical drive circuit across the display area part , Since the necessary buffer circuit can be omitted, the circuit configuration of the reference voltage generation circuit can be simplified accordingly.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating a configuration example of an active matrix display device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a configuration example of a display area unit of a liquid crystal display device.
FIG. 3 is a block diagram illustrating an example of a specific configuration of an H driver.
FIG. 4 is a circuit diagram illustrating an example of a configuration of a reference voltage selection type DA conversion circuit.
FIG. 5 is a circuit diagram showing a general configuration example of a reference voltage generation circuit.
FIG. 6 is a circuit diagram showing a specific configuration example of a reference voltage generation circuit according to the present embodiment.
FIG. 7 is a timing chart for explaining the operation of the reference voltage generation circuit according to the embodiment.
FIG. 8 is an external view showing an outline of a configuration of a mobile phone which is a mobile terminal according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Glass substrate, 12 ... Display area part, 13U, 13D ... H driver (horizontal drive circuit), 14 ... V driver (vertical drive circuit), 15 ... Reference voltage generation circuit, 23 ... Unit pixel, 28U, 28D ... Reference | standard Voltage selection type DA converter circuit, 31, 32 ... switch circuit, 31-1 to 31-n ... buffer circuit

Claims (11)

A display area portion in which pixels having electro-optic elements are arranged in a matrix;
A reference voltage generating circuit for generating a plurality of reference voltages;
A reference voltage selection type DA converter circuit that selects a reference voltage corresponding to digital data from the plurality of reference voltages is provided, and the reference voltage selected by the DA converter circuit is used as an image signal for each pixel in the selected pixel row. A horizontal drive circuit to be supplied to
A pair of the horizontal drive circuits are arranged above and below the display area part,
The reference voltage generation circuit is formed on the same substrate together with the display area unit and the horizontal drive circuit, and sandwiches the pixel array unit with a vertical drive circuit that selects each pixel of the display area unit in a row unit. An active matrix type in which one of the plurality of reference voltages is arranged directly at a position equidistant from the pair of horizontal drive circuits on the opposite side and directly supplies the plurality of reference voltages to the pair of horizontal drive circuits without interposing a buffer circuit Display device. The active matrix display device according to claim 1, wherein the reference voltage generation circuit is formed using the same process together with the display area unit and the horizontal driving circuit. In each pixel of the display area portion, an active element that drives the electro-optic element is formed of a thin film transistor,
The active matrix display device according to claim 1, wherein the horizontal drive circuit and the reference voltage generation circuit are configured using thin film transistors. The active matrix display device according to claim 1, wherein the reference voltage generation circuit is disposed on any one of the sides where the horizontal driving circuit is not disposed on the substrate. The active matrix display device according to claim 1, wherein the electro-optic element is a liquid crystal cell. The active matrix display device according to claim 1, wherein the electro-optic element is an electroluminescence element. A display area portion in which pixels having electro-optic elements are arranged in a matrix;
A reference voltage generating circuit for generating a plurality of reference voltages;
A reference voltage selection type DA converter circuit that selects a reference voltage corresponding to digital data from the plurality of reference voltages is provided, and the reference voltage selected by the DA converter circuit is used as an image signal for each pixel in the selected pixel row. A horizontal drive circuit to be supplied to
A pair of the horizontal drive circuits are arranged above and below the display area part,
The reference voltage generation circuit is formed on the same substrate together with the display area unit and the horizontal drive circuit, and sandwiches the pixel array unit with a vertical drive circuit that selects each pixel of the display area unit in a row unit. An active matrix type in which one of the plurality of reference voltages is arranged directly at a position equidistant from the pair of horizontal drive circuits on the opposite side and directly supplies the plurality of reference voltages to the pair of horizontal drive circuits without interposing a buffer circuit A portable terminal using a display device as a display unit. In each pixel of the display area portion, an active element that drives the electro-optic element is formed of a thin film transistor,
The portable terminal according to claim 7, wherein the horizontal drive circuit and the reference voltage generation circuit are configured using thin film transistors. The portable terminal according to claim 7, wherein the reference voltage generation circuit is disposed on any one of the sides where the horizontal drive circuit is not disposed on the substrate. The mobile terminal according to claim 7, wherein the active matrix display device is a liquid crystal display device using a liquid crystal cell as the electro-optic element. The mobile terminal according to claim 7, wherein the active matrix display device is an electroluminescence display device using an electroluminescence element as the electro-optic element.

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