JPH082650Y2 - Liquid crystal drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a liquid crystal driving device for driving a liquid crystal display panel by a plurality of grayscale signals.

[Prior Art and Problems to be Solved] Conventionally, in a liquid crystal television receiver, a received television video signal is converted into 3- to 4-bit digital data, and a gradation signal is generated from the digital data based on a brightness modulation pulse. The segment electrodes of the liquid crystal display panel are driven by this gradation signal. Although not shown, the brightness modulation pulse is created based on the brightness modulation pulse creation signal c in a brightness modulation pulse generation circuit. As the brightness modulation pulse generation signal c, conventionally, as shown in FIG. 4, one kind of signal which is always output at the same timing even if the liquid crystal drive voltage V changes is used. FIG. 4 shows the generation timing of the brightness modulation pulse creation signal c in the case of 4 gradations. The brightness modulation pulse creation signal c is generated in each cycle of the data latch signal n.
Is output every two shots. When a brightness modulation pulse is created by the brightness modulation pulse creation signal c, a characteristic curve showing the relationship between the liquid crystal drive voltage (effective value) V and the light transmittance T is as shown in FIG. You cannot get the characteristics. That is, even if the liquid crystal drive voltage V is adjusted to a certain value Vi so that the light transmittance T corresponding to the gradation signal is obtained, the liquid crystal drive voltage V is adjusted by the brightness adjustment.
Is changed to the value of Vj, the balance of the light transmittance with respect to the gradation signal is lost, and as a result, it is not possible to always display a good intermediate gradation.

The present invention has been made in view of the above circumstances, and can maintain a predetermined light transmittance balance even when the liquid crystal drive voltage is changed, and can display a good intermediate gradation. The purpose is to provide.

[Means and Actions for Solving the Problems] The present invention provides a liquid crystal driving device for driving a gray scale of a liquid crystal display panel by a gray scale signal.
A memory in which a plurality of types of data for generating a gradation signal corresponding to the light transmittance characteristic are stored in advance, and one of the data stored in the memory is stored according to the liquid crystal drive voltage.
A liquid crystal drive by gradation driving the liquid crystal display panel based on the data for generating the gradation signal stored in the memory, which is selected by the selecting means. Even if the voltage is changed, a predetermined light transmittance balance can always be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 11 is a latch circuit, and the latch circuit 11 is supplied with digital data DA and a latch pulse φv according to a setting position of a brightness adjusting volume (not shown).
A vertical synchronizing signal is used as the latch pulse φv, for example. The latch circuit 11 is the digital data
D / A conversion circuit 12 by latching DA with latch pulse φv
To the upper address pin of ROM13. The D / A conversion circuit 12 converts the data latched by the latch circuit 11 into an analog voltage and outputs it as a liquid crystal drive voltage V to a liquid crystal drive circuit (not shown). Further, 14 is a counter, to which the clock pulse φ is input as a count pulse and the data latch signal n is input as a reset signal. Counter 14 above
Counts the clock pulse φ after being reset by the data latch signal n and outputs the count value to the ROM 13
Input as a lower address to. This ROM 13 stores data for generating the brightness modulation pulse generation signal c, and the stored data is read out to the flip-flop 15 by the above-mentioned upper address and lower address. The flip-flop 15 reads the data read from the ROM 13 by a clock pulse φ and outputs it as a brightness modulation pulse creation signal c. Therefore, data is written in advance in the ROM 13 so that the brightness modulation pulse generation signal .phi.c can be obtained in which the light transmittance characteristic with respect to the liquid crystal drive voltage (effective value) V is ideal. That is, as shown in FIG. 2, an ideal light transmittance T for a certain liquid crystal drive voltage V is obtained.
The time chart for the data latch signal n of the brightness modulation pulse creation signal c that can obtain the balance of
It is written in the lower address part of M13. The data written in the ROM 13 is prepared as a reference table of the brightness modulation pulse creation signal c for various liquid crystal drive voltages V. The data stored in this ROM 13 is the liquid crystal drive voltage (effective value) of the liquid crystal display panel (not shown) used.
-Determined by the measured data on the light transmission properties.

Next, the operation of the above embodiment will be described. Digital data DA is given according to the setting position of the brightness adjustment volume and is latched by the latch circuit 11 in synchronization with the latch pulse φv. The data latched in the latch circuit 11 is converted into an analog voltage in the D / A conversion circuit 12 and sent to the liquid crystal drive circuit as the liquid crystal drive voltage V. Further, the upper address of the ROM 13 is designated by the data latched by the latch circuit 11. On the other hand, the counter 14 is reset by the data latch signal n and then counts up by the clock pulse φ.
Specify the lower address of. According to the designation of the lower address, the storage data of "0" or "1" is sequentially read from the ROM 13 and input to the flip-flop 15. The flip-flop 15 reads the data read from the ROM 13 in synchronization with the clock pulse φ and outputs it as a brightness modulation pulse creation signal c. Now, in the characteristic curve of the liquid crystal drive voltage V and the light transmittance T of FIG. 3, assuming that the liquid crystal drive voltage V set by the brightness adjustment volume is Vi,
As shown in FIG. 2, the flip-flop 15 outputs the brightness modulation pulse generation signal ci corresponding to the liquid crystal drive voltage Vi, and the balance of the light transmittance is kept at the optimum value. Second above
The time chart in the figure shows the case of four gradations.

Then, when the brightness adjustment volume is adjusted to change the brightness of the liquid crystal display panel from the above state, the digital data DA output according to the adjustment is the latch pulse φv.
Since the data is latched by the latch circuit 11 in synchronization with, the liquid crystal drive voltage V output from the D / A conversion circuit 12 changes according to the latch data. Further, the upper address of the ROM 13 is designated by the data latched in the latch circuit 11,
Storage data is sequentially read from the ROM 13 to the flip-flop 15 according to the count value of the counter 14. Therefore, if the liquid crystal drive voltage V rises to Vj by the brightness adjustment, as shown in FIG. 2, the brightness modulation pulse creation signal cj corresponding to the liquid crystal drive voltage Vj from the flip-flop 15, for example, the brightness modulation pulse creation signal. A brightness modulation pulse creation signal cj, which is in phase with respect to ci, is output. As a result, even when the liquid crystal drive voltage V changes to Vj, the light transmittance balance is maintained at the optimum value.

Hereinafter, even when the liquid crystal drive voltage V is adjusted to other values in the same manner, the balance of the light transmittance T is always maintained at the optimum value as shown by the characteristic curve in FIG. As a result,
Even if you adjust the brightness of the liquid crystal display panel,
It is possible to always display good intermediate gradation.

In the above-mentioned embodiment, the address of the ROM 13 is specified by referring only to the digital data DA corresponding to the setting position of the brightness adjustment volume. Brightness modulated pulse creation signal c in which data is also written in ROM 13 and temperature compensation is taken into consideration
May be generated.

[Effect of the Invention] As described in detail above, according to the present invention, the brightness modulation signal is automatically changed according to the liquid crystal driving voltage in consideration of the characteristics of the liquid crystal driving voltage and the light transmittance of the liquid crystal display panel. Since a predetermined light transmittance balance is always obtained even when the liquid crystal drive voltage is changed, it is possible to always perform good halftone display even if the brightness of the liquid crystal display panel is adjusted.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention.
FIG. 1 is a block diagram showing the circuit configuration, FIG. 2 is a time chart for explaining the operation, FIG. 3 is a characteristic curve diagram showing the relationship between liquid crystal drive voltage and light transmittance, and FIG. FIG. 5 is a time chart for explaining the operation of the liquid crystal drive device, and FIG. 5 is a characteristic curve diagram showing the relationship between the liquid crystal drive voltage and the light transmittance in the conventional device. 11 …… Latch circuit, 12 …… D / A conversion circuit, 13 …… ROM, 14
…… Counter, 15 …… Flip-flop.

Claims (1)

[Scope of utility model registration request] 1. A liquid crystal driving device for gradation driving a liquid crystal display panel by gradation signals, wherein plural kinds of data for generating gradation signals corresponding to plural kinds of liquid crystal driving voltage-light transmittance characteristics are stored in advance. Memory and a selection means for selecting one of the data stored in the memory according to the liquid crystal drive voltage, and the gradation stored in the memory selected by the selection means. A liquid crystal drive device, characterized in that a liquid crystal display panel is gradation driven based on data for generating a signal.