JPH0756586B2 - Driving method for positive active matrix panel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called active matrix panel driving method for driving a liquid crystal using active elements.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal has been used as a display body mainly for a timepiece calculator, but in the future, there is an increasing demand for large-capacity display for a computer terminal, a pocket TV, and the like. However, in the conventional voltage averaging method, the drive duty is limited to 1/30 to 1/50, and it is difficult to increase the capacity to about 1/500. Therefore, a transistor such as a thin film transistor (TFT), a metal-insulator-metal (M
1) using an active (IM) element or the like (MIM is not strictly active but is defined in the present invention)
It has been proposed to improve the drive duty by performing writing / holding for each pixel.

FIG . 1 shows (n.times.m) cells arranged in a matrix, and an active matrix panel for performing a write-hold operation by selecting each pixel by n data lines and m gate lines. Is.

FIG . 2 shows the structure and driving method of an active matrix using TFTs for a specific data line D _i . The cell is vertically m from P _{il to} P _im.
Individually arranged, the transistor is turned on by the gate line G _j , the display content is written to the pixel from the data line,
Next, turn off the transistor and until the next selection,
Hold the written data. An equivalent liquid crystal resistor R _L and capacitance C _L are connected to this transistor. This data line is used for the image signal V. By sequentially selecting S from the shift register 1, the capacitance C _si is sample-held via the transistor 2. This is so-called dot sequential driving.

FIG . 3 shows an example of operation waveforms in this dot sequential drive. In order to drive the liquid crystal with an alternating current, one frame is divided into two fields, and a positive voltage is written in an odd field and a negative voltage is written in an even field. Data line potential V
_D is V _DH when the liquid crystal is lit, and V _DL when the liquid crystal is not lit,
For gradation, a voltage within this range is applied. The gate voltage V _G sequentially selects each scanning line from top to bottom as shown in the figure. For example, considering the display of a television screen using about 200 scanning lines, the selection time T _S of one scanning line is 60.
_usec , the field period is 16 msec. Therefore, each pixel is written in 60 usec for 16ms
The contents written during ec are retained. Therefore, each Y line (corresponding to a scanning line) is _generated by the gate signals V _{G1 to} V _Gm.
Are sequentially written, and each pixel has a pixel potential V as shown in (c).
Hold _{Cl to} V _Cm .

Further, in one scanning line period, as shown in FIG. The S input is sampled and held sequentially from V _{D1 to} V _Dn by the sample and hold clock S _H , and this data is written to a predetermined line while the gate signal V _Gj is open.

[0007]

FIG . 5A shows a video input signal used in this system, in which the higher the voltage with respect to the pedestal level, the higher the brightness. This characteristic as shown in FIG 6 the video signal to match the CRT (3 /
It is nothing but because the signal voltage and the luminance are related by the square law . On the other hand, as the characteristics of the liquid crystal panel, the contrast approaches 100% with respect to the voltage as shown in FIG.
That is, the TN type positive display having the characteristic of increasing the black level has the best display characteristic. At this time, the original video signal is set so that the higher voltage level becomes whiter, whereas in the positive type display which is the object of the present invention, the higher voltage level becomes the black level, and the video signal and its The polarity is reversed. Therefore, FIG.
The signal shown in A is inverted as it is to produce a signal B, and the A signal and the B signal are switched for each field to produce the image signal V _D (V.S) shown in FIG. 3 as a liquid crystal AC drive signal .
It is easy to use the circuit. But the video signal is
Since it has the characteristics shown in Fig. 6, it is on the white side as it is.
The gradation is compressed, resulting in an unnatural display. Well
In addition, the display quality itself is
Yes.

It is therefore an object of the present invention is to provide a method of forming a positive image signal which is compatible with the liquid crystal characteristics such as shown in FIG.

[0009]

The positive-acting actuator of the present invention
The driving method of the bus matrix panel is based on the gate signal.
When selected, the image signal is sent to a predetermined pixel via a transistor.
Display operation by writing the signal and holding it when not selected
Positive active matrix panel
Based on a signal obtained by inverting the video signal input.
It is characterized by being formed.

[0010]

FIG . 8 shows an image signal used in the present invention. First, a video obtained by inverting the positive video signal shown in FIG.
Form a signal. And in this inverted video signal
Based on the bias voltage present in this inverted video signal.
The signal C that sets the pressure and this signal C with respect to the reference voltage
The inverted signal D is formed. Then, the signal C and the signal D are switched for each field to form an image signal of a positive type liquid crystal panel .

Further, in order to match the contrast curve of the liquid crystal shown in FIG. 7 , the bias voltage V _B and the amplitude A _V are set to form an image signal that brings the display to an optimum state.

FIG . 9 is a block diagram showing an example of an image signal forming circuit used in the present invention. Video IF output or external video signal V.V. The IF first forms the signal inverted by the inverting amplifier 20. Then symmetric
Based on the inverted signal in the amplifier 21, the reference voltage is compared with
Form the inverted signal by reversing the inverted signal.
It An image signal is generated by a selector 22 and its buffer 23 that alternately switch the forward (+) and the reverse (-) outputs of the symmetrical amplifier 21 for each field by the frame signal Sf.
V. S is formed. Of course there are other examples,
It is included in the present invention to temporarily invert the input video signal of the present invention to obtain an image signal as shown in FIG.

FIG . 10 shows a concrete example of a circuit for forming an image signal of the present invention, and FIG. 11 shows its operation waveform.
Video signal V. The IF is input to the inverting amplifier formed by the transistor 35. This input signal I is applied to the transistor 32
Video signal V. a variable resistor 30, the capacitor 31
The pedestal clamp level V _{B of} the IF input is adjusted, and this V _B is the final image signal V. The bias voltage V _{B of} S is determined. The inverting amplifier is composed of a transistor 35, a collector resistor 34, and emitter resistors 36 and 40. Capacitor 41 and the variable resistor 42 is the amplitude A _V of the output signal E of the inverting amplifier by the impedance of the emitter side to the _variable, the variable, the resulting image signal V.
Amplitude _{A V} of S, can be adjusted. Figure 11E shows the inverting amplifier
It is a signal obtained more . Transistor 45 and resistor 4
Reference numerals 3 and 44 are symmetrical amplifiers, which form symmetrical signals like the signals F and G shown in FIG . A transmission gate, for example a CMOS bilateral switch 46,
The frame 47 alternately selects the signals F and G for each field by the frame signal Sf, and the transistors 48, 49, and 5 are selected.
2, 53, and resistors 50, 51 via a video buffer . Output as S.

[0014] The video signal to be input, as described above, Ru only signal der for the CRT. Therefore, in the present invention, the bidet
Positive display by reversing the E signal in advance and AC driving
Made possible However, the video signal voltage-luminance characteristics and liquid
That of crystal display device is very different. The video signal is set so that the brightness becomes 3/2 of the voltage as shown in FIG. 6 , and therefore the input voltage corresponds to the brightness to be displayed .
It has the characteristics shown in 12 (a). On the other hand, when the video signal is once inverted as in the present invention and the proper bias voltage V _B and width _AV are set, a curve as shown in FIG . Comparing this characteristic of (b) with the characteristic of the liquid crystal used in the present invention of FIG. 7 , it is understood that the black level, that is, the one close to 100% contrast is relatively good, but the white level and the contrast 0% side do not match.
It As a result, it is impossible to reproduce an image in the range from white to gray as it is. Accordingly, performs voltage compression of the white side (luminance extension) to reproduce the characteristics near Le point in contrast curve shown in Figure 7, is improved reproducibility of gradation when as (c). Variable resistor 39 and diode 3 in FIG.
8 is an embodiment for this purpose. Due to the non-linear effect of the diode, as shown in FIG. 13 , the voltage is compressed in the larger amplitude, and this effect is obtained. The variable resistor 39 is for adjusting the degree of compression. This effect is a signal in which the side with the larger amplitude in the signal of FIG. 8 is compressed with both + and −.

[0015]

As described above, the present invention is applicable to video input.
Inverts the signal and creates an image based on this inverted video signal.
The image signal is formed, and further the image formed in this way is formed.
The image signal is formed by compressing the white level of the image signal.
According to the method of the present invention, a video signal for CRT is
TN-type positive liquid with the best display effect under the optimum display conditions
Since it is possible to use a crystal,
Display with high display quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement of a matrix type liquid crystal display device.

FIG. 2 is a diagram showing a drive circuit and a matrix cell of an active matrix panel.

FIG. 3 is a diagram showing drive waveforms applied to the drive circuit of FIG.

FIG. 4 is a diagram showing drive waveforms applied to the drive circuit of FIG.

FIG. 5 is a diagram showing a video signal.

FIG. 6 is a diagram showing luminance-voltage characteristics of a video signal.

FIG. 7 is a diagram showing luminance-voltage characteristics of liquid crystal.

FIG. 8 is a diagram showing an image signal of the present invention.

9 is a block diagram showing an example of a waveform forming circuit that forms the waveform of FIG.

FIG. 10 is a specific circuit diagram of FIG.

11 is a diagram showing operation waveforms in FIG.

FIG. 12 is a diagram showing luminance-voltage characteristics obtained by the present invention.

FIG. 13 is a diagram showing voltage compression characteristics on the white side of the present invention.

[Explanation of symbols]

 1 Data side shift register 20 Inverting amplifier 21 Symmetrical amplifier 22 Selection circuit 23 Buffer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-49995 (JP, A) JP-A-53-148919 (JP, A) JP-A-50-49999 (JP, A)

Claims (2)

[Claims] 1. A positive active matrix panel for performing a display operation by writing an image signal to a predetermined pixel through a transistor when selected based on a gate signal and holding the pixel signal when not selected, wherein the image signal is a video signal.
A method for driving a positive active matrix panel, which is formed based on a signal obtained by inverting an input . 2. The image signal according to claim 1, wherein the white level side is voltage-compressed.
Driving method for bogey type active matrix panel.