LCD driver

Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix

Reexamination Certificate

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Details

C345S089000, C345S210000, C345S211000

Reexamination Certificate

active

06275209

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an LCD driver for driving an LCD (liquid crystal display) in accordance with display data fed from a separately provided microcomputer, and particularly to an LCD driver for driving a dot-matrix LCD.
2. Description of the Prior Art
FIGS. 6A and 6B
illustrate how a conventional LCD driver is used. As shown in
FIG. 6A
, a conventional LCD driver
73
, when used in a portable phone or other appliance that incorporates a microcomputer
72
for controlling the entire appliance and an LCD
74
, is placed between the microcomputer
72
and the LCD
74
, so that the LCD driver
73
, by being fed with display data from the microcomputer
72
, drives the LCD
74
.
Such an appliance is also provided with an nonvolatile data-storage device
71
such as an EEPROM (electrically erasable programmable read-only memory) for storing setting data so that a predetermined degree of contrast can be readily obtained in accordance with such factors as the type and use of the appliance. In the assembly process of the appliance, the contrast of the image displayed on the LCD
74
is adjusted to the desired degree, and the setting data for an electronic variable resistor at that time is stored in the data-storage device
71
.
When this appliance is in actual use, the contrast of the LCD
74
is adjusted, as shown in
FIG. 6B
, by letting the microcomputer
72
read the setting data from the data-storage device
71
and feed it to the LCD driver
73
. This helps prevent different LCDs
74
from exhibiting unduly different contrast as a result of variations in their characteristics that inevitably occur in their production.
However, storing the setting data for the electronic variable resistor in the data-storage device provided as a separate component requires the assembly process of the appliance such as a portable phone to include a step for adjusting the contrast of the display, that is, it necessitates an extra step in the assembly process. In addition, letting the microcomputer
72
read the setting data for the electronic variable resistor from the data-storage device
71
and feed it to the LCD driver
73
increases the operational burden to be borne by the microcomputer
72
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an LCD driver that does not require an extra step for contrast adjustment in the assembly process of an appliance such as a portable phone that is fitted with an LCD. Another object of the present invention is to provide an LCD driver that does not require a microcomputer to perform extra operations for contrast adjustment.
To achieve the above objects, according to one aspect of the present invention, an LCD driver for driving a dot-matrix LCD in accordance with display data fed from a microcomputer is provided with a rewritable nonvolatile data-storage circuit for storing data concerning an electronic variable resistor for setting the contrast of the LCD.
With this LCD driver, it is only after the LCD to be driven has been determined that contrast is adjusted and the setting data for the electronic variable resistor is stored in the nonvolatile data-storage circuit of the LCD driver. As a result, it is no longer necessary to adjust contrast while an appliance such as a portable phone is assembled from components including the LCD driver and the microcomputer. Nor is it necessary to provide as a separate component a data-storage device for storing the setting data for the electronic variable resistor.
In this LCD driver, the above-mentioned nonvolatile data-storage circuit may be realized as an EEPROM. In that case, it is possible, when the LCD driver is manufactured, to integrate the EEPROM readily into the same chip as the LCD driver simply by slightly modifying the manufacturing process of CMOS (complementary metal-oxide semiconductor). In addition, it is also possible to use the voltage step-up circuit provided in the LCD driver both for driving the LCD and for effecting the writing of data to the EEPROM.


REFERENCES:
patent: 5745092 (1998-04-01), Ito
patent: 5798741 (1998-08-01), Kajihara
patent: 5986649 (1999-11-01), Yamazaki

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