JP2890960B2 - Drive circuit for liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a liquid crystal display, and more particularly, to a driving circuit for a liquid crystal display which uses 16 bits based on 4-bit display data.
The present invention relates to a liquid crystal display driving circuit capable of outputting one of the voltage levels of a value and capable of displaying 16 gradations.

[0002]

2. Description of the Related Art A conventional driving circuit for a liquid crystal display comprises:
It is possible to perform 8-gradation display in which one of eight voltage levels is output based on 3-bit display data.
As an example, FIG. 5 shows a liquid crystal drive circuit of HD66310T made by Hitachi. The 3-bit display data D ₀ , D ₁ , and D ₂ are taken into the latch circuit 1 by the clock CL1. After the capture of the display data for one horizontal time is completed, the data is collectively transferred to the latch circuit 2 with the clock pulse CL2. The transferred display data, and controls the voltage selector 3 selects one of the eight levels of voltage V ₀ ~V _7.

It is technically possible to develop the design of a conventional drive circuit for an 8-gradation liquid crystal display into 16 gradations. Further, a method of optically realizing two frames between the eight gradations (in increments of 0.5) using the driving circuit for an eight gradation liquid crystal display, that is, one frame out of 52 frames is set as a higher gradation. There has been proposed a method of realizing 16 gradations by selecting a lower gradation for the other frame.

[0004]

When the conventional driving circuit for an 8-gradation liquid crystal display is expanded to 16 gradations,
Since the number of analog switches for selecting the voltage level is doubled and the number of wirings is quadrupled, there is a practical difficulty.
Also, the method of using this 8-gradation liquid crystal display driving circuit to realize 16 gradations by the driving method has a problem in that the image quality is inferior.

[0005]

A driving circuit for a liquid crystal display according to the present invention sequentially takes in 4-bit display data into a latch circuit, and after completing the taking-in of display data for one horizontal time, collectively operates other latches. After the display data is transferred to the circuit, the voltage selector is controlled by the lower 3 bits of display data, and one of eight externally input voltage levels is output.
A circuit is provided for selecting and outputting a level, and selecting whether or not to shift the voltage level according to the display data of the most significant one bit being "1" or "0".

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows one output of the liquid crystal display drive circuit according to the first embodiment of the present invention. The display data D ₀ , D ₁ , D ₂ , and D ₃ input in time series are taken into the latch circuit 1 by the clock pulse C ₁ . After all the outputs n within one horizontal time have been taken into the latch circuit 1,
The data is collectively transferred to the latch circuit ₂ by the clock pulse C2. The voltage selector 3 is controlled by the three bits of the transferred display data D ₀ , D ₁ , and D ₂ ,
From the output, eight analog switches 5 based on the display data
Are turned on, and the voltage levels V ₀ , V ₁ ,
_{V 2, V 3, V 4} , reads one of _{V 5, V 6, V 7} .

The output voltage level is branched, one of which is supplied to the analog switch 6a, and the other of which is supplied to the level shifter 4a.
After shifting the level by the voltage V, the signal reaches the analog switch 6b. If the most significant bit D ₃ is "1", the analog switch 6 analog switch 6b is turned
If a is cut off and "0", conduction and cut-off are reversed. FIG. 2 shows a voltage level output according to the present embodiment. One value is selected from 16 values in the figure.

FIG. 3 is a drive circuit diagram of a second embodiment of the present invention. This embodiment is obtained by adding a function of reversing the polarity of the voltage level every vertical time or every horizontal time to the first embodiment. When the signal R for inverting the polarity is “0”, the power switcher 8 sets V _{0 to} V
₇ is selected, and the same voltage level as in the first embodiment is output. On the other hand, in the case of the signal R is "1", 1 value of the voltage level of the 16 values 'to _{V 0' V 7 '~V 0} ' is selected V ₇ to + V is outputted by the power supply switcher 8 . FIG. 4 shows the voltage levels output according to the second embodiment. One value is selected from 16 values for each polarity.

[0009]

As described above, the present invention provides the conventional 8
A level shifter for shifting the voltage is added to the drive circuit for the liquid crystal display of the value level, and it is configured to select whether or not to shift the level by the most significant one bit of the 4-bit display data. A 16-level liquid crystal display driving circuit can be realized with a small addition to the level liquid crystal display driving circuit. That is, the present invention has an effect that the chip size in the case of being integrated can be manufactured with a chip size which is almost the same as the conventional one.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing an output voltage level of the drive circuit shown in FIG. 1;

FIG. 3 is a circuit configuration diagram of a second embodiment of the present invention.

FIG. 4 is a diagram schematically showing an output voltage level of the drive circuit shown in FIG. 3;

FIG. 5 is a circuit configuration diagram of a conventional liquid crystal display drive circuit.

[Explanation of symbols]

 1, 2 latch circuit 3 voltage selector 4 level shifter 5, 6 analog switch 7 exclusive NOR circuit 8 power switcher

Claims (1)

(57) [Claims] 1. A liquid crystal display drive circuit having n outputs, which takes in 4-bit display data per output and selectively outputs one of 16 voltage levels based on the 4-bit display data. The level A, which is one of eight levels of voltage input from the outside selected and output by the lower three bits of the display data of the bits, is changed to the level A, and the display data of the most significant one bit of the four bits of the display data is “ A drive circuit for a liquid crystal display, comprising: a circuit for selecting whether or not the level A is shifted by 1 "or" 0 ".