Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-08-16
2004-09-21
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S089000
Reexamination Certificate
active
06795046
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the field of image display devices, and more particularly to liquid crystal display devices, and to calibration circuitry for such devices.
2. Description of the Related Art
Image display devices such as liquid crystal display (LCD) devices are widely known. With reference to the following description, familiarity with conventional features of such devices will be assumed, so that only features bearing on the present invention will be described.
FIG. 1
shows relevant portions of an exemplary liquid crystal display (LCD) device
100
.
The LCD device
100
comprises in relevant part: a plurality of pixels
110
; a plurality of column (data) lines
120
connected to the plurality of pixels
110
; a plurality of column (data) drivers
130
for supplying data to pixels
110
via the column lines
120
; a plurality of column driver switches
140
; a plurality of row (scanning) lines
150
connected to rows of pixels
110
; and a plurality of row drivers
160
connected to the row lines
120
for selecting a row of pixels
110
to which data from the column drivers
130
is to be applied.
Typically, each pixel
110
includes a pixel switching device
112
and a storage device (pixel capacitor)
114
. The pixel switching device
112
, which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line
150
to switch a data signal applied via the connected column line
120
into the storage device
114
.
The LCD device
100
may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers
130
, column driver switches
140
, and/or row (scanning) drivers
160
may be integrated onto a same silicon substrate as the liquid crystal pixels
110
.
Image data is provided as digital input data from an external video generator to the column drivers
130
. However, the column drivers
130
must provide analog image data to the column lines
120
. Hence, the image data is subjected to signal processing, including digital to analog conversion, in the column drivers
130
.
Some problems with the prior art LCD device
100
will now be explained.
Variations between the column drivers
130
and column lines
120
cause a situation wherein the pixels
110
of two different column lines
120
may display different brightnesses (intensities) even though the same digital image data is applied to the column driver(s)
130
for both column lines
120
. Indeed, the variations may be so great that a situation occurs wherein a column driver
130
for a first column line
120
receives first digital image data having a greater value than second digital image data received by a column driver
130
for a second column line
120
, and yet the pixels
110
of the second column line
120
actually display a brighter image (greater intensity) than the pixels
110
of the first column line
120
. These variations result in an undesirable display characteristic.
Moreover, the signal processing in the column drivers
130
produces non-linearities in the image data. Because of these non-linearities, the brightness range of the image data does not monotonically increase. In other words, one or more situations may occur wherein the digital image data value for a particular column line
120
is increased, but the actual displayed brightness displayed by the pixels
110
of the column line
120
decreases.
In general, propagation delays of digital and analog signals in the device
100
, in addition to common circuit property variations (e.g., amplifier offsets; gain/bandwidth variations) cause brightness variations between pixels or regions (e.g., columns) of the display.
Accordingly, it would be desirable to provide an image display device with reduced or eliminated brightness level variations among pixels or columns receiving the same digital input data. It also would be desirable to provide an image display device having a brightness that monotonically increases in response to digital input data received form an external video signal generator.
SUMMARY OF THE INVENTION
Accordingly, in one aspect, an image display device includes a plurality of pixels arranged in a matrix or rows and columns, a plurality of column lines each connected to a corresponding one of the columns of pixels, at least one column driver providing a data voltage to one of the column lines, a generator producing a reference voltage, and means for comparing the reference voltage to the data voltage and in response thereto producing a calibration data error value.
In another aspect, a method of calibrating data voltage levels for image display device including a plurality of pixels arranged in a matrix of rows and columns, a plurality of column lines connected to the plurality of pixels, and a plurality of column drivers connected to the column lines and providing data to the pixels, includes: generating a reference signal; receiving P-bit digital input data having a digital input data value; producing a data voltage on one of the column lines in response to the received digital input data; and comparing the reference signal to the data voltage produced on one of the column lines and, in response thereto, generating a calibration data error value.
REFERENCES:
patent: 4840462 (1989-06-01), Hartmann
patent: 5625373 (1997-04-01), Johnson
patent: 5751279 (1998-05-01), Okumura
patent: 6229508 (2001-05-01), Kane
patent: 6331846 (2001-12-01), Nakao
patent: 0729233 (1996-08-01), None
patent: 0953959 (1999-11-01), None
patent: 0953959 (1999-11-01), None
patent: 05-265405 (1993-10-01), None
Matsueda et al: “30.1: 6-Bit-Color VGA Low-Temperature Poly-SI TFT-LCD With Integrated Digital Data Drivers” 1998 SID International Symposium Digest Of Technical Papers. vol. 29, May 17, 1998, pp. 879-882.
Furuhashi et al: “A g4-Gray-Scale Digital Signal Driver For Color TFT-LCDS” SID International Symposium Digest Of Technical Papers. vol. 25, Jun. 14, 1994, pp. 359-362.
Albu Lucian Remus
Janssen Peter J.
Eisen Alexander
Hjerpe Richard
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