JP2003233350A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption by controlling current loss in a step-up circuit of a liquid crystal display device. <P>SOLUTION: The liquid crystal display device always detects an output value of a video signal 16 outputted from a group of signal electrode driving circuits, and compares the difference between the output voltage value of the group of signal electrode driving circuits and the voltage value of the input power source 101, and thereby controls at any time during a single horizontal period whether to drive signal electrodes by the input power source 101 or whether to drive the signal electrodes by the output converted by a D/A converter circuit 14 and amplified by an amplifier circuit 13. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device useful as a display of a video device such as a television, an information device such as a computer, and a mobile phone. 2. Description of the Related Art FIG. 5 is a block diagram of a liquid crystal display device often used in recent years, FIG. 4 is a detailed diagram thereof, and FIG. It is a waveform. In FIG. 5, reference numeral 101 denotes an input power supply input to the liquid crystal display device, 102 denotes an input signal input to the liquid crystal display device, 141 denotes a control signal circuit for processing a control signal and a video signal, and 144 denotes a power supply. Circuit control signal, 111
, A power supply circuit for generating a power supply used for the scanning electrodes and the signal electrodes from the input power supply 101; 112, a power supply for the signal electrode drive circuit; 113, a power supply for the scan electrode drive circuit; 521, a signal electrode drive circuit group; Numeral 523 denotes a signal for a signal electrode driving circuit, 531 denotes a scanning electrode driving circuit group, 53
2 is a scan electrode, 533 is a signal for a scan electrode drive circuit, 50
9 is a liquid crystal panel, and 18 is a pixel of the liquid crystal panel. [0004] The operation of the conventional liquid crystal display device configured as described above will be described below. In the conventional liquid crystal display device shown in FIG. 5, a scanning electrode 532 and a signal electrode 522 are provided on a liquid crystal panel 509, and a pixel 18 is provided at each intersection. The signal electrode driving circuit group 521 and the scanning electrode driving circuit group 531 drive the signal electrode 522 and the scanning electrode 532, respectively. The control signal generation circuit 141 processes an image to be displayed on the liquid crystal display device into a video signal to be provided to the signal electrode drive circuit group 521 or generates a control signal for controlling the signal electrode drive circuit group 521 based on the input signal 102. Or as a signal 523 for a signal electrode drive circuit.
The signal is sent to the signal electrode drive circuit group 521, and the input signal 10
Based on 2, a power supply circuit control signal 144 for operating the power supply circuit 111 is generated and sent to the power supply circuit 111. In the power supply circuit 111, the power supply required for the signal electrode drive circuit group 521 and the scan electrode drive circuit group 533 is generated by the power supply circuit control signal 144, and the input voltage 101 is sent to each of the electrode drive circuit groups. In the signal electrode drive circuit group 521, a signal electrode signal is generated by the signal electrode drive power supply 112 from the power supply circuit 111, the video signal from the control signal generation circuit 141, and the signal electrode drive signal 523 which is a control signal. Then, the signal electrode 522 is driven. Also, the scan electrode drive circuit group 53
1, the scan electrode driving power supply 11 from the power supply circuit 111
3 and a scan electrode driving signal 533 which is a control signal from the control signal generation circuit 141, to generate a scan electrode signal and drive the scan electrode 532. In this way, a display image is displayed on each pixel of the liquid crystal display device by the generated signal electrode signal and scanning electrode signal. Here, the flow of signals will be described in more detail below with reference to FIG. In FIG. 4, reference numeral 101 denotes an input power source,
02 is an input signal, 141 is a control signal circuit, 144 is a power supply circuit control signal, 111 is a power supply circuit, 112 is a power supply for a signal electrode drive circuit, 142 is a control signal for a signal electrode drive circuit,
Reference numeral 421 denotes a signal electrode drive circuit group output unit, 13 denotes an amplifier circuit, 14 denotes a digital / analog circuit (hereinafter, referred to as a D / A circuit), and 15 denotes a booster circuit for a signal electrode drive circuit power supply (hereinafter, referred to as an AVDD booster circuit). , 16 is a video signal,
Reference numeral 17 denotes a signal electrode drive signal, and reference numeral 18 denotes a pixel. [0009] With respect to the operation of the conventional liquid crystal display device configured as described above, a signal flow in a portion for displaying an image not touched in the above will be described below. The signal electrode drive circuit group output section 421 of the signal electrode drive circuit group 521 of the conventional liquid crystal display device comprises a D / A circuit 14 and an amplifier circuit 13, each of which is provided by a control signal generation circuit 141. Is controlled on the basis of the control signal 142 for the signal electrode drive circuit. On the other hand, in the power supply circuit 111, a power supply to be used in the signal electrode drive circuit group by the AVDD booster circuit 15 in the power supply circuit 111 is generated from the input power supply 101 and supplied to the signal electrode drive circuit group 521. The D / A circuit 14 and the amplifier circuit 13 are operated by these power supplies and signals. Here, a signal from the input signal 102 is subjected to signal processing in a video signal processing unit in the control signal circuit 141 to generate a video signal 16 which is an n-bit digital signal usable in a liquid crystal display device. Signal 16 is applied to D / A circuit 1
In step 4, the analog signal is converted into an analog amount corresponding to the digital signal, and the analog video signal is amplified by the amplifier circuit 13 and transmitted to the liquid crystal pixel 18 as a signal electrode drive signal 17. The pixel 18 is turned on / off by a scanning electrode signal,
It comprises a pixel transistor for conducting and blocking the signal electrode signal 17, a pixel electrode, a counter electrode, and a liquid crystal layer formed between the electrodes. In accordance with the scan electrode signal, while the pixel transistor is on, the signal electrode signal 17 conducts the pixel transistor and is applied to the pixel electrode, and charges are accumulated in the liquid crystal pixel from the signal electrode signal 17 side for a specified time. Then, the twist angle of the liquid crystal layer is controlled by the signal potential difference between the signal electrode and the counter electrode, and then the pixel transistor is turned off by the scanning electrode signal to hold the image information. By performing such an operation for each pixel on a scanning line basis, an image is displayed on the liquid crystal display device. Next, using the signal waveform of FIG.
The potential difference and the image display described above will be described in more detail. In FIG. 3, reference numeral 22 denotes a power supply circuit section operation, 23 denotes a signal electrode drive circuit section output operation, 25 denotes a step-up operation, 26 denotes a signal electrode drive circuit group power supply, 101 denotes an input voltage, and 317 denotes a signal electrode drive. A signal waveform, 321 is a signal electrode drive circuit group power supply current, and 322 is an input power supply current. The signals in the conventional liquid crystal display device will be described with the waveforms configured as described above. First, the power supply circuit 111 applies the input voltage 101 to the AVDD booster circuit 15.
Then, the boosting operation 25 is performed so that the voltage level changes from the input voltage 101 to the signal electrode drive circuit group power supply 26, and the voltage value is raised. The boosted power is supplied to the D / A circuit 14 and the amplifier circuit 13 of the signal electrode drive circuit group,
The signal electrode drive signal waveform 317, which is the output signal of the signal electrode drive circuit group,
N input to the D / A circuit 14 between the ND level VSS and the power supply voltage of the signal electrode drive circuit group power supply 26
It takes an arbitrary value defined by the bit digital video data. Normally, the pixel transistor is turned on at the "Hi" level of the scan electrode signal and turned off at the "Lo" level. When the scanning electrode signal is at the “Hi” level, the counter signal converted into AC every one horizontal period is applied to the counter electrode, synchronized with the counter signal, and the video signal 3 converted into AC every one horizontal period is output.
17 conducts the pixel transistor so that the signal level is changed from the negative signal level to the positive signal level or from the positive signal level to the negative signal level, and is applied to the pixel electrode. At this time, if the liquid crystal characteristics are white with no voltage applied, and if it is desired to display white on the pixels of the liquid crystal display device, the potential difference between the opposing signal and the video signal becomes zero.
(V) is applied so that a twist angle is hardly generated in the liquid crystal layer. Conversely, if black is to be displayed, the voltage is set so that the potential difference between the opposing signal and the video signal becomes large. To increase the twist angle in the liquid crystal layer, and if an intermediate color is to be displayed, the potential difference is given an arbitrary potential between white display and black display, and the twist angle is appropriately generated in the liquid crystal layer. I have to. However, when displaying with the waveform of FIG. 3, when the signal level reaches the signal level from the negative side, or when the signal level reaches the positive side, When the signal level reaches the negative side, the electric charge for charging or discharging the pixel capacitor, that is, the current, is supplied from the signal electrode drive circuit group power supply voltage 26 which is the voltage obtained by performing the boosting operation 25 on the input voltage 101. The larger the boost value of the AVDD boost circuit 15 of the circuit 111, the larger the current flowing to the input voltage 101. For example, when the value of the signal electrode drive circuit group power supply 26 is twice the input voltage 101,
Since the DD boosting circuit 15 doubles the input voltage 101, the current flowing through the signal electrode drive circuit group power supply 26 is doubled when converted to the input voltage 101. The input voltage is VCC, the current flowing through the input voltage is IVCC, and the voltage obtained by boosting VCC by the booster circuit is AVDD.
Suppose that the current flowing through AVDD is IAVDD,
Since VDD = VCC × 2 times, IVCC = IAV
DD × 2. Until the potential of the signal electrode drive signal waveform reaches potential saturation, the signal electrode drive circuit group power supply 26 continues to flow current until the potential is saturated like the signal electrode drive circuit group power supply current 321. Keep flowing. This allows
When the power supply circuit 111 has no loss, when converted to the input power supply 101, the value becomes twice the value of the signal electrode drive circuit group power supply current 321 like the input power supply current 322. Since the power supply circuit 111 has a loss, the current further increases. In other words, by boosting the signal electrode drive circuit group power supply 26 from the input power supply 101, unnecessary power continues to be consumed, causing an increase in power consumption of the liquid crystal display device. In view of the foregoing, it is an object of the present invention to provide a liquid crystal display device having a configuration for suppressing power consumption, which is the above problem, and realizing low power consumption. In order to solve the above-mentioned problems, the present invention provides a method in which a scanning electrode and a signal electrode are formed in a matrix, and the scanning electrode and the signal electrode intersect each other. A pixel is provided with a pixel electrode, a liquid crystal layer is provided between the pixel electrode and a counter electrode facing the pixel electrode, and a liquid crystal for displaying an image by controlling a twist angle of the liquid crystal by a potential difference between the pixel electrode and the counter electrode. A panel, a scan electrode drive circuit group for driving the scan electrodes, a digital / analog circuit for converting an n-bit digital video signal, which is a video signal, into an analog amount, and a signal electrode for amplifying the converted analog video signal. The power supply used by the signal electrode drive circuit group composed of an amplifier circuit and the scan electrode drive circuit group and the signal electrode drive circuit group, which is sent to the A power supply circuit capable of supplying the driving circuit group and the signal electrode driving circuit group, and a video signal to be transmitted to the signal electrode driving circuit group, and controlled by the scanning signal electrode circuit group, the signal electrode driving circuit group, and the power supply circuit What is claimed is: 1. A liquid crystal display device comprising: a control signal circuit for transmitting a signal; and a wiring board for supplying a data signal, a control signal, and power. During a period in which a large voltage value is generated and the digital / analog circuit and the amplifier circuit are driven to send a video signal to the signal electrode, the output value of the video signal output from the signal electrode drive circuit group is converted to the digital / analog signal.
The digital data value converted by the analog circuit is always detected, the difference between the output voltage value of the signal electrode drive circuit group and the input power supply voltage value of the liquid crystal display device is compared, and a control signal output from the control signal circuit is used. Controlling whether to drive the signal electrode with an input power supply or to drive the signal electrode with an output converted by a digital / analog circuit and amplified by the amplifier circuit;
A liquid crystal display device characterized in that a signal sent to a signal electrode is switched at an arbitrary time within one horizontal period. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram of a liquid crystal display according to an embodiment of the present invention, and FIG. 2 shows signal waveforms of the embodiment. In FIG. 1, reference numeral 101 denotes an input power source;
02 is an input signal, 141 is a control signal circuit, 142 is a control signal for a signal electrode drive circuit, 144 is a power supply circuit control signal,
111 is a power supply circuit, 112 is a power supply for a signal electrode drive circuit,
121 is a signal electrode drive circuit group output unit, 11 is a VCC charging circuit, 12 is a VCC charging control signal, 13 is an amplifier circuit,
14 is a D / A circuit, 15 is an AVDD booster circuit, 16 is a video signal, 17 is a signal electrode drive signal, and 18 is a pixel. An embodiment of the present invention will be described with reference to the liquid crystal display device configured as described above. The signal electrode drive circuit group output section 121 of the liquid crystal display device according to the present invention comprises a D / A circuit 14 and an amplifier circuit 13.
An n-bit digital video signal 16, a signal electrode driving circuit signal 142 for controlling the signal electrode driving circuit group output section 121, and an n-bit digital signal. A VCC charge control signal 12 for controlling the VCC charge circuit 11 according to the video signal 16 and a power supply circuit control signal 1 for controlling the power supply circuit 111
44, and the input power 101
Is supplied to the D / A circuit 14 and the amplifier circuit 13 by the AVDD booster circuit 15 to generate a power supply 112 for a signal electrode drive circuit. The VCC charging circuit 11 processes the input signal 102 generated by the control signal circuit 141,
The value of the n-bit digital video signal 16 processed into a signal to be applied to the signal electrode, the input power supply 101 and the input power supply 101
A signal electrode is directly driven by the input power supply 101 or an n-bit digital signal is converted into an analog signal by the D / A circuit 14 according to a voltage difference, that is, a boost difference of the signal electrode drive circuit power supply 112 created from The VCC charge control signal 12 determines whether the signal is driven by the signal amplified by the amplifier circuit 13, and the input power supply 101 and the signal that is the output signal of the amplifier circuit 13 are arbitrarily defined for one horizontal period. And the pixel 18 can be charged and discharged as the signal electrode drive signal 17. Next, using the signal waveform of FIG.
The potential difference between the power supply voltages described above and the switching between the driving by the input power supply 101 and the driving by the output signal of the amplifier circuit 13 within an arbitrary prescribed time will be described in more detail. In FIG. 2, reference numeral 22 denotes a power supply circuit section operation, 23 denotes a signal electrode drive circuit section output operation, 25 denotes a step-up operation, 26 denotes a signal electrode drive circuit group power supply, 27 denotes a VCC charging period, and 101 denotes an input voltage. , 211 are signal electrode drive signal waveforms, 221 is a signal electrode drive circuit group power supply current, and 231 is an input power supply current. First, an input voltage 101
AVDD booster circuit 15 sets the voltage level to input power supply 10
The boosting operation 25 is performed so that the signal electrode driving circuit group power source 26 changes from 1 to increase the voltage value. Here, the description will be made simply on the assumption that the input voltage 101 and the signal electrode drive circuit group power supply voltage 26 are double, that is, the boosting operation 25 is double. The signal electrode drive circuit group power supply 26, which is a power supply that has been boosted twice, is supplied to the D / A circuit 14 and the amplifier circuit 13 of the signal electrode drive circuit group, and is an output signal of the signal electrode drive circuit group. The signal electrode drive signal waveform 211 is GND
An arbitrary value defined by n-bit digital video data input to the D / A circuit 14 is taken between the VSS level which is the level and the signal electrode driving circuit group power supply 26 which is the power supply voltage level. . Normally, when the signal level reaches the signal level positive side from the signal level negative side, or when the signal level reaches the signal level negative side from the signal level positive side, the electric charge to be charged or discharged to the pixel capacitor, that is, the current, is input. The voltage 101 is all supplied from the signal electrode drive circuit group power supply voltage 26 which is a voltage obtained by performing the boosting operation 25, and the value of the signal electrode drive circuit group power supply voltage 26 is twice the value of the input voltage 101. , AVDD booster circuit 15 has a signal electrode driving power supply 26
Is converted to the value of the input power supply 101,
Double. That is, since AVDD = VCC × 2 times, IVCC = IAVDD × 2 times. Here, in the present invention, when the signal level reaches the signal level negative side from the negative side, that is, when the pixel capacitor is charged, VCC which is an arbitrary time within one horizontal period is used.
In the charging period 27, the pixels are directly charged by the input power supply 101 from the negative side of the signal electrode drive signal 211 to the potential of the input power supply 101, and the potential of the input power supply 101 is maintained in the remaining period of one horizontal period. Is charged from the output signal of the amplifier circuit 13 to the potential on the positive side of the signal electrode drive signal 211, the signal electrode drive signal 211 is charged in two stages. The value of the flowing current at this time is
When the value is converted into the value, the current from the negative side of the signal electrode drive signal 211 to the potential of the input power supply 101 becomes a current that is one time of the input power supply 101, and from the potential of the input power supply 101 to the potential on the positive side of the signal electrode drive signal 211. Is a signal electrode drive circuit group power supply current 221 which is a current flowing through the signal electrode drive power supply 26.
Is doubled when converted to the value of the input power supply 101.
When these are summed, a current value like the input power supply current 231 is obtained. That is, from the negative side to the VCC potential, the IVC
C = IVCC = VCC potential to the positive side, IVCC =
IAVDD × 2 times. Here, assuming that the current value from the negative side to the VCC potential is I1 and the current value from the VCC potential to the positive side is I2, the current flowing through the input power supply 101 is conventionally
(I1 + I2) × 2, and in the present invention, I1 + I2
× 2. (Conventional current value)-(Current value of the present invention)
= I1, the current for I1 can be suppressed, and the power consumption can be reduced. Actually, since the loss always occurs in the booster circuit of the power supply circuit 111, this current further increases. However, no loss occurs only in the input power supply 101. Then, (I1 +
I2) × 2 × (1 + loss rate).
1 + I2 × 2 × (1 + loss rate). (Conventional current value)-(Current value of the present invention) = I1 (1 + 2 × the loss rate)
And the current of I1 (1 + 2 × the loss rate) can be suppressed,
Low power can be achieved. Since there is usually a loss, the greater the loss, the greater the effect of further reducing power consumption. That is, the signal electrode drive signal 21
1 is a VCC charging period 27 which is an arbitrary period
By setting the value to 01, unnecessary power consumption can be suppressed and the power consumption of the liquid crystal display device can be reduced as compared with the case where the input power supply 101 is always driven by the boosted signal electrode driving power supply 26. Although the embodiment of the present invention has been described with the boosting being doubled, the boosting ratio may be any value as long as it is a value of 1 or more. Further, for each liquid crystal display device, the most optimal VCC charging period 27 is individually considered in consideration of the variation in the writing capability of the signal electrode drive circuit group 16 to the pixels and the variation in the load of the pixels 17 of the liquid crystal. So that it can be set,
The least wasteful liquid crystal display device with low power consumption can be realized. As described above, according to the present invention, current loss in the booster circuit of the liquid crystal display device can be suppressed by the above configuration, and as a result, power consumption can be suppressed. Liquid crystal display device can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a configuration of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a signal waveform of the liquid crystal display device according to an embodiment of the present invention. FIG. 4 is a diagram showing a signal waveform of a liquid crystal display device. FIG. 4 is a detailed configuration diagram of a conventional liquid crystal display device. FIG. 5 is an overall configuration diagram of a conventional liquid crystal display device. Description of reference numerals 11 VCC charging circuit 12 VCC charging control signal 13 Amplifier circuit 14 D / A circuit 15 AVDD booster circuit 16 Video signal 17 Signal electrode drive signal 18 Pixel 22 Power supply circuit section operation 23 Signal electrode drive circuit section output operation 25 Boosting operation 26 Signal electrode drive circuit group power supply 27 VCC charging period 101 Input Power supply 102 Input signal 141 Control signal circuit 142 Signal electrode drive circuit control signal 144 Power supply circuit control signal 111 Power supply circuit 112 Signal electrode drive circuit power supply 121 No. electrode drive circuits output unit 211 the signal electrode driving signal waveform 221 signal electrode driving circuits supply current 231 input supply current

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 G09G 3/20 612G 612U 623 623D F-term (Reference) 2H093 NC02 NC11 NC13 NC16 ND39 5C006 AA01 AC21 AF45 AF69 AF71 AF82 BB16 BC12 BF14 BF25 BF42 BF46 FA47 5C080 AA10 BB05 DD26 FF11 GG08 JJ02 JJ04

Claims (1)

Claims: 1. A scanning electrode and a signal electrode are formed in a matrix, and a pixel electrode is provided for each pixel where the scanning electrode and the signal electrode intersect. A liquid crystal layer is provided between the pixel electrode and a counter electrode facing the pixel electrode, and controls a twist angle of liquid crystal by a potential difference between the pixel electrode and the counter electrode. A scanning electrode driving circuit group to be driven, a digital / analog circuit for converting an n-bit digital video signal which is a video signal into an analog amount, and an amplifier circuit for amplifying the converted analog video signal and sending it to the signal electrode. A power supply used in the configured signal electrode drive circuit group, the scan electrode drive circuit group, and the signal electrode drive circuit group is voltage-converted from an input power supply by a booster circuit, and the scan electrode drive circuit A power supply circuit capable of supplying a power supply to the group and the signal electrode drive circuit group; a video signal to be transmitted to the signal electrode drive circuit group; and the scan signal electrode circuit group, the signal electrode drive circuit group, and the power supply circuit. And a wiring board for supplying a data signal, a control signal, and a power supply, and the signal electrode drive circuit group is a booster circuit of the power supply circuit. A video signal which is an output of the signal electrode drive circuit group during a period in which a voltage value larger than the voltage value of the input power supply is generated and the digital / analog circuit and the amplifier circuit are driven to send a video signal to the signal electrode; Is always detected by the digital / analog circuit, and the difference between the output voltage value of the signal electrode driving circuit group and the input power supply voltage value of the liquid crystal display device is calculated. A control signal output from the control signal circuit controls whether the signal electrode is driven by the input power supply or the signal electrode is driven by an output converted by a digital / analog circuit and amplified by the amplifier circuit. A liquid crystal display device wherein a signal to be sent to a signal electrode is switched at an arbitrary time within one horizontal period.