JPH0782304B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device using a CRT controller.

[Conventional technology]

In recent years, a CRT controller IC used with a controller circuit such as a color simple graphic display using a cathode ray tube (CRT) as a display means is used as a controller of a liquid crystal panel to configure a liquid crystal display device such as a liquid crystal character display. Have been studied (Japanese Patent Laid-Open No. 60-15
9779 publication).

[Problems to be solved by the invention]

Since the liquid crystal display device configured in this way is normally driven by the voltage averaging method, the number of time divisions of display increases by about the vertical retrace time of the CRT controller (about 10%), and the operating margin increases. However, there is a problem in that the display contrast is slightly reduced.

It is an object of the present invention to provide a liquid crystal display device that does not reduce the display contrast without reducing the operation margin even when there is a period (vertical retrace time) unrelated to display.

[Means for solving problems]

In order to achieve the above object, the present invention provides a liquid crystal panel having at least a liquid crystal layer and a plurality of signal lines and scanning lines arranged on both sides of the liquid crystal layer so as to be orthogonal to each other, and a plurality of liquid crystal panels of the liquid crystal panel. Liquid crystal module including a plurality of segment drive circuits for applying a drive voltage to a signal line, and a plurality of scan drive circuits for applying a drive voltage to a plurality of scan lines of the liquid crystal panel, and operation of the liquid crystal module In a liquid crystal display device comprising a CRT controller for controlling, and a voltage supply circuit that supplies a plurality of liquid crystal drive voltages to each drive circuit, a period unrelated to display is detected based on a specific signal of the CRT controller, A voltage divider circuit comprising an identification circuit for outputting an identification signal, wherein the voltage supply circuit divides a predetermined drive voltage to generate the plurality of liquid crystal drive voltages. , Provided at one end of said divider circuit, characterized by comprising a switching element which is non-conducting by the identification signal of the identification circuit.

[Action]

According to the above means, the discrimination circuit detects a period irrelevant to the display, whereby the switching element of the voltage supply circuit is made non-conductive, and the same drive voltage is applied to the signal line and the drive line of the liquid crystal display panel. As a result, the voltage applied to the liquid crystal layer during the period irrelevant to the display can be set to almost zero voltage, which reduces the operation margin of the liquid crystal display device even during the period irrelevant to the display. Without this, it is possible to prevent the display contrast from decreasing.

〔Example〕

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

Normally, when a liquid crystal panel is driven in a time-division manner, the drive voltage applied to the liquid crystal panel is reversed in polarity within two frame times in which all the scanning lines of the display screen are scanned twice, and the AC voltage is converted to AC
System drive is mainly used. FIG. 1 shows liquid crystal panel drive voltage waveforms by this voltage averaging method. FIG. 1A shows an ON waveform, FIG. 1B shows an OFF waveform, 1 / a bias, time division number. This is the case of N. In this case, the effective voltage V of the ON and OFF waveforms of the applied voltage V _O
ON and V _OFF are as follows.

The operation margin is V _ON / V _OFF, which is expressed by the following equation.

Here, if there is a period αt ₁ irrelevant to the display such as the vertical blanking time of the CRT controller, the number of time divisions increases by that amount. In this case, the operating margin is
The operating margin is reduced.

Next, in the period αt ₁ irrelevant to the display, the applied voltage waveform when the drive voltage applied to the liquid crystal panel is set to zero
Shown in the figure. In the figure, (a) is an on-waveform and (b) is an off-waveform, and αt ₁ is a period unrelated to display. The number of display lines is N, and the number of time divisions is N + α. In this case, the effective voltage V _'ON Oyo V' _OFF ON waveform and OFF waveform of the applied voltage becomes the following equation.

Therefore, the operation margin becomes the following expression, which is equal to the expression (3).

Next, an embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a block circuit diagram showing an embodiment of the liquid crystal display device according to the present invention. In FIG. 1, reference numeral 1 denotes a liquid crystal module composed of a liquid crystal panel and its drive circuit,
A controller circuit 2 controls the operation of the liquid crystal module 1. 3a, 4b, 4c, 3a having at least a liquid crystal layer and a plurality of signal lines and scanning lines arranged on both sides of the liquid crystal layer so as to be orthogonal to each other, and having display pixels arranged in a matrix. , 4d, 4e, 4f, 4g, 4h are liquid crystal panel 3
The segment side drive circuit that outputs a signal voltage to the signal lines Y _{1 to} Y ₄ and Y _{5 to} Y ₈ in the Y-axis direction, 5a and 5b are the scanning lines X ₁ and X ₂ in the X-axis direction of the liquid crystal panel 1 sequentially. A scanning side drive circuit that outputs a selection pulse for scanning, 6 is a segment side drive circuit 4a
4h and the scanning side drive circuits 5a, 5b are driven by the voltage averaging method, as shown in FIG. 4, each voltage level V ₁ , V ₂ , V ₃ , V ₄ , V ₅ , V
₆ is a voltage supply circuit having a voltage dividing circuit 6a for generating 6 and a switching element 6b for making the voltage dividing circuit 6a high impedance or disconnecting the voltage dividing circuit 6a, and 7 is a predetermined driving voltage for the voltage supplying circuit 6, that is, a positive driving voltage V _DD And negative drive voltage V _EE
Is a voltage control circuit 8 for supplying a display data latch signal CL ₁ , a display data shift signal CL ₂ , a display synchronization signal FLM, as a timing signal for operating the liquid crystal module 1.
A timing generation circuit for outputting an alternating signal M for reversing the polarities of the liquid crystal display data DATA 'and the applied voltage,
9 is a latch signal CL ₁ , a display timing signal DSPTMG output from the CRT controller 10 or a vertical synchronization signal VSYNC
Is a discriminating circuit which discriminates a period irrelevant to the display by using and outputs the discriminating signal. From the CRT controller 10, the oscillator output signal OSC, the character clock signal (CRT controller clock) CLK, the display timing signal DISPTMG,
The horizontal synchronizing signal HSYNC, the vertical synchronizing signal VSINC and the CRT display data DATA are output respectively.

Further, FIGS. 5A to 5L show timings of output signals of various circuits in the B system drive of the controller circuit 2 shown in FIG. 3, and display timings of FIG. The signal DISPTMG, the horizontal synchronizing signal HSYNC in the figure (h) and the latch signal CL _{1 in} the figure (j) are respectively shown in the figure (c),
(D) and (f) are compressed and shown.

In such a configuration, the oscillator output signal OSC output from the CRT controller 10, the clock signal CLK, the display timing signal DISPTMG, the horizontal synchronization signal HSYNC, the vertical synchronization signal VSIN
Output signals such as C and CRT display data DATA are input to the timing generation circuit 8, and a latch signal CL ₁ for driving the liquid crystal module ₁ , a display data shift signal CL ₂ , a display synchronizing signal FLM, liquid crystal display data DATA ′ and The voltage is converted into an AC signal M for inverting the polarity of the applied voltage and supplied to the segment side drive circuits 4a-4h and the scan side drive circuits 5a, 5b at predetermined timings. On the other hand, the voltage control circuit 7 is a carrier output of the scanning side driving circuits 5a, 5b including any output signal of the N + 1th line (display is N line) or more of the scanning side driving circuits 5a, 5b or the Nth line output signal. The signal Sc is input. On the other hand, the identification circuit 9 has CR
The display timing signal DISTMG or the vertical synchronizing signal VSYNC is input from the T controller 10, and the latch signal CL ₁ is input from the timing generation circuit 8, and a period unrelated to the display of the CRT controller 10 is identified and the identification signal Ss is output. , The switching element 6b (see FIG. 4) which is output from the power supply control circuit 7 to the voltage supply circuit 6 and controls the drive voltage V _DD of the liquid crystal panel 3 by the identification signal Ss output during this period is made high impedance (resistance). (Infinity) or by disconnecting, each voltage level V _{1 to} V ₆ applied to both drive circuits 4a to 4h, 5a, 5b becomes substantially equal to the drive voltage V _{EE of the} negative electrode and applied to the liquid crystal panel 3. The driving voltage becomes almost zero.

FIG. 6 is a block diagram of a voltage supply circuit showing another embodiment of the liquid crystal display device according to the present invention. In the figure, the fourth
The difference from the figure is that the switching element 6b drives the negative drive voltage.
Connected to V _EE side. Even in such a configuration, by switching the switching element 6b to a high impedance state or disconnecting it, each voltage level V _{1 to} V ₆ becomes substantially equal to the positive drive voltage V _DD, and the voltage applied to the liquid crystal panel 3 is almost the same. It becomes zero.

〔The invention's effect〕

As described above, according to the present invention, by using the CRT controller, the switching element of the voltage supply circuit is made non-conductive and the signal line and the drive line of the liquid crystal display panel are disconnected even during a period unrelated to display. Since the same drive voltage is applied, the voltage applied to the liquid crystal layer during the period irrelevant to the display can be set to almost zero voltage.

As a result, it is possible to prevent the display contrast from decreasing with a simple circuit configuration without reducing the operation margin of the liquid crystal display device. Therefore, since the widely used CRT controller can be used without any problems, it becomes easy to use it for the controller of the liquid crystal display device, and it becomes possible to incorporate a drive system close to the CRT graphic display, and the user can use it. It is possible to obtain extremely excellent effects such as the configuration of an easy-to-use system.

[Brief description of drawings]

1 (a) and 1 (b) are diagrams showing an on waveform and an off waveform of a liquid crystal drive voltage waveform by a voltage averaging method, and FIGS. 2 (a) and 2 (b).
(B) is an ON waveform and an OFF waveform of a liquid crystal drive voltage waveform relating to the liquid crystal display device according to the present invention, FIG. 3 is a block circuit diagram showing one embodiment of the liquid crystal display device according to the present invention, and FIG. 4 is FIG. 5 is a detailed circuit diagram of the voltage supply circuit, FIG. 5 is an operation timing diagram of the liquid crystal display device shown in FIG. 3, and FIG. 6 is a detailed circuit diagram of the voltage supply circuit showing another embodiment of the liquid crystal display device according to the present invention. It is a circuit diagram. 1 ... Liquid crystal module, 2 ... Controller circuit, 3 ...
… Liquid crystal panel, 4a-4h …… Segment side drive circuit, 5a, 5
b ... Scanning side drive circuit, 6 ... Voltage supply circuit, 6a ... Voltage dividing circuit, 6b ... Switching element, 7 ... Voltage control circuit, 8 ... Timing generation circuit, 9 ... Identification circuit, 10 ... … CRT controller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoshige Kinugawa 3300 Hayano, Mobara-shi, Chiba Hitachi Ltd. Mobara factory (56) References JP-A-60-159779 (JP, A) JP-A-59-78394 (JP, A)

Claims (1)

[Claims] 1. A liquid crystal panel having at least a liquid crystal layer and a plurality of signal lines and scanning lines arranged on both sides of the liquid crystal layer so as to be orthogonal to each other, and a drive voltage is applied to the plurality of signal lines of the liquid crystal panel. For driving a plurality of segment drive circuits, a plurality of scan drive circuits for applying a drive voltage to the plurality of scan lines of the liquid crystal panel, and a CRT for controlling the operation of the liquid crystal module
In a liquid crystal display device including a controller and a voltage supply circuit that supplies a plurality of liquid crystal drive voltages to each drive circuit, a period unrelated to display is detected based on a specific signal of the CRT controller, and an identification signal thereof is output. A voltage dividing circuit, wherein the pre-voltage supply circuit divides a predetermined drive voltage to generate the plurality of liquid crystal drive voltages,
A liquid crystal display device, comprising: a switching element which is provided at one end of the voltage dividing circuit and is made non-conductive by an identification signal of the identification circuit.