Note: Descriptions are shown in the official language in which they were submitted.
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"DRIVING APPARATUS FOR AN ACTIVE ADDRESSED DISPLAY".
Field of the Invention
10
This invention relates in general to electronic displays, and more
specifically to a method and apparatus for driving an active addressed,
root-mean-square (rms) responding display system to reduce memory
requirements and power consumption.
Background of the Invention
An example of a direct multiplexed, rms responding electronic
display is the well-known liquid crystal display (LCD). In such displays, a
nematic liquid crystal material is positioned between two parallel glass
plates having electrodes applied to each surface in contact with the liquid
crystal material. The electrodes typically are arranged in vertical columns
on one plate and horizontal rows on the other plate for driving a picture
element (pixel) wherever a column and row electrode overlap. A high
2 0 information content display, e.g., a display used as a monitor in a
portable
laptop computer, requires a large number of pixels to portray arbitrary
patterns of information. Matrix LCDs having four hundred eighty rows
and six hundred forty columns forming 307,200 pixels are widely used in
computers today, and matrix LCDs with millions of pixels are expected
soon.
In so-called rms responding displays, the optical state of a pixel is
substantially responsive to the square of the voltage applied to the pixel,
i.e., the difference in the voltages applied to the electrodes on the opposite
sides of the pixel. LCDs have an inherent time constant that characterizes
3 0 the time required for the optical state of a pixel to return to an
equilibrium
state after the optical state has been modified by changing the voltage
s applied to the pixel. Recent technological advances have produced LCDs
with time constants approaching the frame period used in many video
displays (approximately 16.7 milliseconds). Such a short time constant
allows the LCD to respond quickly and is especially advantageous for
depicting motion without noticeable smearing of the displayed image.
An active addressing method is typically used to optimize the
contrast ratio of an LCD being used for video information display. In the
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typically used active addressing method, video information consisting of
frames of image values is organized in a sequence of rows of image values
which are transmitted to the display system. Each image value represents
a value (gray scale values in a black and white, gray scale system) of a pixel
in the image which is to be presented at a pixel in the display. T'he active
addressing method continuously drives the row electrodes with signals
comprising a train of periodic pulses having a common period T
corresponding to the frame period. The row signals are independent of
the image to be displayed and preferably are orthogonal and normalized,
i.e., orthonormal. The term orthogonal denotes that if the amplitude of a
signal applied to one of the rows is multiplied by the amplitude of a signal
applied to another one of the rows, the- integral of this product over the
frame period is zero. The term normalized denotes that all the row
signals have the same rms voltage integrated over the frame period T.
A problem with active addressing results from the large number of
calculations required per second. For example, a gray scale display having
four hundred eighty rows and six hundred forty columns, and a frame rate
of 60 frames per second requires just under ten billion calculations per
second. Typical currently available display systems using active addressing
2 0 have two sets of video image memory, each set capable of storing the four
hundred eighty by six hundred forty image values, each image value being
typically an eight bit value. One of the sets of memory is used to assemble
a frame of image values on a row by row basis, while the second set of
memory is used as a source of image values in which columns of the
image values remain constant for a frame period. Such constancy of
column information is important to prevent fitter and smearing of the
image. Although it is possible with today's technology to perform
calculations at the rate described, the architectures proposed to date for
calculation engines used for actively addressed displays have not been
3 0 optimized to minimize- memory requirements. The memory requirement
issue is particularly important in portable applications, wherein excessive
memory results in an excessive power requirement, larger parts, and a
higher cost of the memory. The excessive power requirement is
particularly important in such portable applications as battery-powered
3 5 laptop computers, in which size,- and battery life are primary design
considerations.
PT00985U
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Thus, what is needed is a method and apparatus for controlling and
driving an actively addressed display in a manner that minimizes the
memory requirements and thus also minimizes the power consumption
and size of the image processing system.
Summary of the Invention
In a first aspect of the present invention, a display system processes an
input signal to generate an image. The input signal includes successive
l0 frames of data, each defining a plurality of successively transmitted lines
of image values. The lines have a line direction. The display system
includes an active addressed display, a video memory, a controller, a
calculation engine, a first driver element, and a second driver element.
The active addressed display is for displaying the image and has ~
plurality of first electrodes and a plurality of second electrodes which cross
each other at intersection points forming pixels. The plurality of second
electrodes are in a direction corresponding to the line direction. The video
memory comprises a single line buffer and a single frame buffer. The
single line buffer is coupled to the input signal and is for accumulating a
2 0 stored line which includes one of the plurality of successively
transmitted
lines of image values. The single frame buffer is coupled to the single
line buffer and is for storing a frame of data including a plurality of the
stored lines. The controller is coupled to the video memory. The
controller transfers the stored line from said single line buffer into said
single frame buffer after the stored line is completely stored in said single
line buffer and generates a predetermined image independent function
having at least M values during a time slot. The calculation engine is
coupled to the controller and the video memory. The calculation engine
computes an image dependent output signal during the time slot. The
image dependent output signal has N values. Each of the N values is
determined from the predetermined image independent function and one
of N sets of image values. The calculation engine reads each of the N sets
of image values from a different one of the plurality of the stored lines
stored in said single frame buffer. The first driver element is coupled to
3 5 the controller and the active addressed display. During the time slot the
first driver circuit generates at M first voltages which are coupled to M
first
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electrodes. Each of the M first voltages is proportional to one of the at
least
M values. The second driver element is coupled to the calculation engine
and the active addressed display. During the time slot the second driver
element generates N second voltages which are coupled to N second
electrodes. Each of the N second voltages is proportional to one of the N
values.
In a second aspect of the present invention, a display system processes
an input signal to generate an image. The input signal includes successive
frames of data defining a plurality of successively transmitted columns of
image values. The display system includes an active addressed display, a
video memory, a controller, a calculation engine, a row driver element,
and a column driver element.
The active addressed display is for displaying the image and has a
plurality of row electrodes and a plurality of column electrodes which
cross each other at intersection points forming pixels. The video memory
is for storing the frame of data and includes a single column buffer and a
single frame buffer. The single column buffer is coupled to the input
signal and is for accumulating a stored column which includes one of the
plurality of successively transmitted columns of image values. The single
2 0 frame buffer is coupled to the single column buffer and is for storing a
frame of data comprising a plurality of the stored columns. The controller
is coupled to the video memory. The controller transfers the stored
column from said single column buffer into said single frame buffer while
image values from a corresponding stored column are not being read from
2 5 said single frame buffer and after the stored column is completely stored
in said single column buffer. The controller generates a predetermined
image independent function having at least M values during a time slot
The calculation engine is coupled to the controller and the video memory.
The calculation engine computes an image dependent output signal
3 0 during the time slot. The image dependent output signal has N values.
Each of the N values is determined from the predetermined image
independent function and one of N sets of image values, and wherein said
calculation engine reads each of the N sets of image values from a
different one of the plurality of the stored columns stored in the single
3 5 frame buffer. The row driver element is coupled to the controller and the
active addressed display. The row driver circuit generates M row voltages
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which are coupled to M row electrodes. Each of the M row voltages is
proportional to one of the M values during the time slot. The column
driver element is coupled to the calculation engine and the active
addressed display. The column driver element generates N column
5 voltages. which are coupled to N column electrodes. Each of the N
column voltages is proportional to one of the N values during the time
slot.
In a third aspect of the present invention, a method is for use in an
electronic device which processes a input signal to generate an image on
an active addressed display. The input signal includes a frame of data
defining a plurality of successively transmitted lines of image values. The
plurality of successively transmitted lines have a line direction. The
method includes the steps of accumulating, transferring, generating,
reading, computing, repeating, generating first voltages, and generating
second voltages.
In the step of accumulating, a stored line comprising one of the
plurality of successively transmitted lines of image values is accumulated
in a single line buffer. In the step of generating, a predetermined image
independent function having at least M values is generated during a time
2 0 slot. In the step of reading, a plurality of image values is read from one
of
the plurality of the stored lines stored in the single frame buffer. In the
step of computing, one of N values of an image dependent output signal is
computed during the time slot. Each of the N values is determined from
the predetermined image independent function and the plurality of image
values read in the step of reading. In the step of repeating, the steps of
reading and computing are repeated N times during the time slot, using a
different one of the plurality of the stored lines for each repetition. In the
step of generating first voltages, M first voltages are generated during the
time slot which are coupled to M first electrodes of the active addressed
3 0 display. Each of the M first voltages is proportional to one of the at
least M
values of the predetermined image independent function. In the step of
generating second voltages, N second voltages are generating during the
time slot which are coupled to N second electrodes of the active addressed
display which have a direction corresponding to the line direction. Each
3 5 of the N second voltages is proportional to one of the N values.
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In a fourth aspect of the present invention, an electronic device
includes a microcomputer, an enclosure, and a display system. The
microcomputer is for transmitting an input signal including successive
frames of data, each frame defining a plurality of successively transmitted
lines of image values. The plurality of successively transmitted lines have
a line direction. The enclosure is coupled to the microcomputer for
supporting and protecting the microcomputer and display system. The
display system is coupled to the microcomputer and processes the input
signal to generate an image. The display system includes an active
addressed display, a video memory, a controller, a calculation engine, a
first driver element, and a second driver element.
The active addressed display is for displaying the image and has a
plurality of first electrodes and a plurality of second electrodes which cross
each other at intersection points forming pixels. The plurality of second
electrodes are in a direction corresponding to the line direction. The video
memory comprises a single line buffer and a single frame buffer. The
single line buffer is coupled to the input signal and is for accumulating a
stored line which includes one of the plurality of successively transmitted
lines of image values. The single frame buffer is coupled to the single
2 0 line buffer and is for storing a frame of data including a plurality of
the
stored lines. The controller is coupled to the video memory. The
controller transfers the stored line from said single line buffer into said
single frame buffer after the stored line is completely stored in said single
line buffer and generates a predetermined image independent function
having at least M values during a time slot. The calculation engine is
coupled to the controller and the video memory. The calculation engine
computes an image dependent output signal during the time slot. The
image dependent output signal has N values. Each of the N values is
determined from the predetermined image independent function and one
3 0 of N sets of image values. T'he calculation engine reads each of the N
sets
of image values from a different one of the plurality of the stored lines
stored in said single frame buffer. The first driver element is coupled to
the controller and the active addressed display. During the time slot the
. first driver circuit generates at M first voltages which are coupled to M
first
3 5 electrodes. Each of the M first voltages is proportional to one of the at
least
M values. The second driver element is coupled to the calculation engine
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and the active addressed display. During the time slot the second driver
element generates N second voltages which are coupled to N second
electrodes. Each of the N second voltages is proportional to one of the N
values.
Brief Description of the Drawings
FIG. 1 is a front orthographic view of a portion of a conventional
liquid crystal display.
FIG. 2 is an orthographic cross-section view along the line 2-2 of FIG.
1 of the portion of the conventional liquid crystal display.
FIG. 3 is an eight-by-eight matrix of Walsh functions in accordance
with the preferred embodiment of the present invention.
FIG. 4 depicts drive signals corresponding to the Walsh functions of
FIG. 3 in accordance with the preferred embodiment of the present
invention.
FIG. 5 is an electrical block diagram of a display system in accordance
with the preferred embodiment of the present invention.
FIG. 6 is an electrical block diagram of a processing system of the
2 0 display system in accordance with the preferred embodiment of the
present invention.
FIG. 7 is an electrical block diagram of a display system in accordance
with a first alternate embodiment of the present invention.
FIG. 8 is an electrical block diagram of an rms correction factor
calculator of the processing system in accordance with the preferred and
alternate embodiments of the present invention.
FIG. 9 is an electrical block diagram of a calculation engine of the
processing system in accordance with the preferred and alternate
embodiments of the present invention.
3 0 FIG. 10 is an electrical block diagram of a controller of the processing
system in accordance with the preferred and alternate embodiments of the
present invention.
FIG. 11 is an electrical block diagram of a personal computer in
accordance with the preferred and alternate embodiments of the present
invention.
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FIG. 12 is a front orthographic view of the personal computer in
accordance with the preferred and alternate embodiments of the present
invention.
FIG. 13 is a flow chart depicting the operation of loading the video
memory in accordance with the preferred and first alternate embodiments
of the present invention.
FIG. 14 is a flow chart depicting the operation of the rms correction
factor calculator in accordance with the preferred and alternate
embodiments of the present invention.
FIG. 15 is a flow chart depicting the operation of the calculation
engine in accordance with the preferred and alternate embodiments of the
present invention.
Detailed Description of the Preferred Embodiment
A display processing system in accordance with a preferred and
alternate embodiments of the present invention is described in more
detail below in which the display processing system drives a display
having first electrodes and second electrodes to display an image which is
2 0 transmitted to the display processing system in successive frames
consisting of lines of image values, in which the direction (row or
column) of the lines corresponds to the direction of the second electrodes.
During each of a plurality of time slots, the first electrodes are driven with
a predetermined image independent signal and the second electrodes are
25 driven with an image dependent signal. During each time slot, the image
dependent signal has a plurality of values, one for each second electrode.
The unique architecture described below in accordance with the preferred
and alternate embodiments of the present invention calculates each value
of the image dependent signal based on only one line of transmitted image
3 0 values, which minimizes image value memory requirements and
interconnection requirements of the display processing system.
Referring to FIGs. 1 and 2, orthographic front and cross-section views
of a portion of a conventional liquid crystal display (LCD) 100 depict first
and second transparent substrates 102, 206 having a space therebetween
3 5 filled with a layer of liquid crystal material 202. A perimeter seal 204
prevents the liquid crystal material from escaping from the LCD 100. The
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LCD 100 further includes a plurality of transparent electrodes,
comprising
row electrodes 106 positioned on the second transparent substrate
206, and
column electrodes 104 positioned on the first transparent
substrate 102. At
each point at which a column electrode 104 overlaps a row
electrode 106,
such as the overlap 108, voltages applied to the overlapping
electrodes 104,
106 can control the optical state of the liquid crystal material
202
therebetween, thus forming a controllable picture element
(pixel). While
an LCD is the preferred display element in accordance with
the preferred
embodiment of the present invention, it will be appreciated
that other
types of display elements may be used as well, provided that
such other
types of display elements exhibit an optical characteristics
responsive to
the square of the voltage applied to each pixel, similar
to the rms response
of an LCD.
Referring to FIGS. 3 and 4, an eight-by-eight (third order)
matrix of
i5 W alsh functions 300 and the corresponding Walsh waves 400
in
accordance with the preferred embodiment of the present invention
are
shown. Walsh functions are orthonormal and are preferable
for use in an
actively addressed display system, as discussed in the Background
of the
Invention herein above. When used in such a display system,
voltages
2 0 having levels represented by the Walsh waves 400 are uniquely
applied to
a selected plurality of electrodes of the LCD 100. For example,
the Walsh
waves 404, 406, and 408 could be applied to the first (uppermost),
second,
and third row electrodes 106, respectively, and so on. In
this manner each
of the Walsh waves 400 would be applied uniquely to a corresponding
one
25 of the row electrodes 106. It is preferable not to use the
Walsh wave 402 in
an LCD application, because the Walsh wave 402 would bias
the LCD with
an undesirable DC voltage.
It is of interest to note that the values of the Walsh waves
400 are
constant during each time slot T. The duration of the time
slot T for the
3 0 eight Walsh waves 400 is one-eighth of the duration of one
complete cycle
of Walsh waves 400 from start 410 to finish 412. When Walsh
waves are
. used for actively addressing a display, the duration of one
complete cycle
of the Walsh waves 400 is set equal to the frame duration,
i.e., the time to
receive one complete set of data for controlling all the
pixels 108 of the
3 5 LCD 100.
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The eight Walsh waves 400 are capable of uniquely driving up to
eight row electrodes 106 (seven if the Walsh wave 402 is not used). It will
be appreciated that a practical display has many more rows. For example,
displays having four-hundred-eighty rows and six-hundred-forty columns
5 are widely used today in laptop computers. Because Walsh function
matrices are available in complete sets determined by powers of two, and
because the orthonormality requirement does not allow more than one
electrode to be driven from each Walsh wave, a five-hundred-twelve by
five-hundred-twelve (29 x 29) Walsh function matrix would be required to
10 drive a display having four-hundred-eighty row electrodes 106. For this
case the duration of the time slot T is 1 /512 of the frame duration. Four-
hundred-eighty Walsh waves would be used to drive the four-hundred-
eighty row electrodes 106, while the remaining thirty-two would be
unused, preferably including the first Walsh wave 402 having a DC bias.
Referring to FIG. 5, an electrical block diagram of a display system 500
in accordance with the preferred embodiment of the present invention
comprises a plurality of processing systems 510 coupled to a data input line
508, preferably eight bits wide, for receiving an input signal including
successive frames of data to be displayed. The successive frames of data
2 0 define image values, which are grouped into lines. The lines are vertical
scans, or columns of image values, in accordance with the preferred
embodiment of the present invention. The successive frames of data
include six hundred forty of the lines, each consisting of four hundred
eighty serially transmitted image values. The LCD 100 is of conventional
2 5 design, having four hundred eighty row electrodes, hereafter referred to
as
first electrodes, extending horizontally across the LCD 100 and two sets of
column electrodes, hereafter referred to as second electrodes. It will be
appreciated that the lines of image values have a vertical, or column,
direction which corresponds to the second set of electrodes. Each set of
3 0 second (column) electrodes extends vertically from an edge (upper or
lower) almost to the center of the display 501, each second (column)
electrode thereby crossing one half of the first (row) electrodes. This
conventional electrode organization reduces the amount of calculations
performed by each processing system and improves the contrast and
3 5 maximum frame rate of the display system for prior art active addressed
displays, as well as in the display system 500 in accordance with the
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preferred embodiment of the present invention, in a simple and cost
effective manner. This type of arrangement of the second display
electrodes is referred hereinafter as split second electrodes. To reduce
calculation requirements for each of the processing systems 510 the LCD
100 has been partitioned into eight areas 511, each serviced by one of the
processing systems 510, and each containing one-hundred-sixty column
electrodes 104 and two-hundred-forty row electrodes 106. It will be
appreciated that the Walsh matrix necessary in the preferred embodiment
of the present invention is of size 28 x 28 (256 x 256), and therefore the
time slot, T, is 1 /256th of a frame period.
The processing systems 510 are coupled by image dependent (column)
output lines 512, preferably eight bits wide, to video digital-to-analog
converters (DACs) 502, such as the model CXD1178Q DAC manufactured
by Sony Corporation, for converting the digital output signals on the
image dependent (column) output lines 512 into corresponding analog
second (column) drive signals. The DACs 502 are coupled to second
(column) drive elements 504 of an analog type, such as the model
SED1779DOA driver manufactured by Seiko Epson Corporation, for
driving the second (column) electrodes 104 of the LCD 100 with the analog
2 0 second (column) drive signals. Two of the processing systems 510 are also
coupled by image independent (row) output lines 514 to first (row) drive
elements 506 of a digital type, such as the model SED1704 driver also
manufactured by Seiko Epson Corporation, for driving the first (row)
electrodes 106 of the upper and lower partitions of the LCD 100 with a
predetermined set of Walsh signals. It will be appreciated that other
similar components can be used as well for the DACs 502, the second
(column) drive elements 504, and the first (row) drive elements 506.
The second (column) and first (row) drive elements 504, 506 receive
and store a batch of drive level information intended for each of the
3 0 second (column) and first (row) electrodes 104, 106 for the duration of
the
time slot T (FIG. 4). The second (column) and first (row) drive elements
504, 506 then substantially simultaneously apply and maintain the drive
levels for each of the second (column) and first (row) electrodes 104, 106 in
accordance with the received drive level information until a next batch,
3 5 e.g., a batch corresponding to the next time slot T, is received by the
second
(column) and first (row) drive elements 504, 506. In this manner the
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transitions of the drive signals for all the second (column) and first (row)
electrodes 104, 106 occur substantially in synchronism with one another.
Referring to -FIG. 6, an electrical block diagram of one of the
processing systems 510 of the display system in accordance with the
preferred embodiment of the present invention comprises a controller
622, a video memory 640, an image dependent output calculator 650, and
an image independent function- shift register 614. The video memory 640
comprises a line buffer 602 and a frame buffer 608. The data input line 508
is coupled to the-line buffer 602. The line buffer 602 is coupled to the
controller 622 by a timing signal 639. The line buffer is for receiving two
hundred forty serially transmitted image values from a single line of a
frame of data, for storing the two hundred forty image values, and for
outputting the two hundred forty image values on a parallel bus 633. It
will be appreciated that the line buffer 602 is storing a portion of a single
complete line of four hundred- eighty image values because the processing
system 500 is processing one block 511 of image values for the display 100,
and thus may alternatively be referred to as a partial single line buffer 602.
The timing signal 639 provides synchronization with the transmitted
image values. The line buffer 602 comprises conventional input circuits,
conventional counters, conventional random access memory (RAM),
conventional control logic, and conventional shift register elements of
sufficient, but not excessive, size inter coupled in a conventional manner
to provide the described function of receiving, storing, and transferring a
single line of image values. It will be appreciated that in some display
systems 500 the input signal may be analog, in which event the display
system 500 may also comprise an analog to digital converter for generating
a digital signal which is coupled to the line buffer 602.
The parallel bus 633 couples the line buffer 602 to the frame buffer 608
for transferring the line of image values into the frame buffer 608 when a
3 0 complete line of image values has been received and erasing a
corresponding line of image values transferred into the frame buffer 608
from the previous frame of data. The parallel bus 633 is a two hundred
forty by eight bit wide bus. The frame buffer 608 is a RAM having
sufficient, but not excessive, storage locations to store one hundred sixty
lines of two hundred forty image values comprised of conventional
memory, input, output, and addressing elements, with the memory,
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addressing, input and output organized for conventional parallel
input
and output of the line of image values. It will be appreciated
that the
frame buffer 608 is storing a portion of a single complete
frame of six
hundred twenty lines because the processing system 500 is
processing ona
block 511 of image values for the display 100, and thus the
single frame
memory 608 may alternatively be referred to as a partial
single frame
buffer 608.
The controller 622 is coupled by a control bus 624 to the
line buffer 602
and the frame buffer 608 for controlling the operation of
the line buffer 602
and the frame buffer 608. The controller 622 is further coupled
by the
control bus 624 to an image independent function shift register
614 for
controlling the operation of the image independent function
shift register
614. The controller 622 is coupled by an image independent
function bus
635 for transferring a predetermined image independent function
generated by the controller 622 to the image independent
function shift
register 614. The image dependent output calculator 650 comprises
an rms
correction factor calculator 632, a correction factor buffer
601, and a
calculation engine 610. The controller 622 is further coupled
by the control
bus 624, by a timing signal 637, and by a virtual value signal
656 to the
2 0 calculation engine 610 for controlling the operation of the
calculation
engine 610. The controller 622 is also coupled by the control
bus 624 to the
rms correction factor calculator 632 for controlling the
rms correction
factor calculator 632, and by the timing signal 639 for providing
image
value synchronization with the input signal on the data input
line 508.
2 5 The rms correction factor calculator 632 is also coupled
to the data input
line 508 for receiving the lines of image values to determine
a correction
factor for each of the lines, as explained herein below in
reference to FIG. 7.
The correction factor buffer 601 is coupled to the rms correction
factor
calculator 632 by a first correction factor signal 607 for
receiving and storing
3 0 the correction factor determined by and sent from the rms
correction factor
calculator 632 for each line. The controller 622 is further
coupled by
control bus 624 to the correction factor buffer 601 for controlling
the
correction factor buffer 601. Each correction factor is stored
for one frame
period in the correction factor buffer 601 which stores one
hundred sixty
3 5 correction factors corresponding to the one hundred sixty
most recently
received lines of image values. The correction factor buffer
601 is coupled
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to the image independent function shift register 614 by a second correction
factor signal 609 for transferring a correction factor to the calculation
engine 610.
The image values within the frame buffer memory 608 are organized
by the controller 622 into blocks, each block corresponding to substantially
all the pixels 108 controlled by a single group of second electrodes 104, the
group size determined in accordance with the present invention, and the
second electrodes 104 falling within the area 511 serviced by the processing
system 510. The block sizes are one hundred sixty lines of two hundred
forty image values, as described above. The controller 622 controls the
operation of the line buffer 602 and the frame buffer 608 to convert and
store the image values for one predetermined block of the blocks in a
frame of data. When a complete line of image values within the
predetermined block is transmitted on data input line 508, the controller
622 controls the line buffer 602 to transfer the image values stored in the
line buffer 602 to a predetermined line location in the frame buffer 608
corresponding to the line of image values transmitted.
The frame buffer memory 608 is coupled by a parallel data bus 630 to
the calculation engines 610 for calculating values for driving the second
2 0 electrodes 104 for each Walsh signal time slot T. The parallel data bus
630
is sufficiently wide to transmit simultaneously image values for
substantially all the pixels 108 controlled by a single group of second
electrodes 104 and falling within the area 511 of the LCD 100 serviced by
the processing system 510. For example, in the processing system 510
servicing two-hundred-forty rows and having eight-bit pixel values, the
parallel data bus 630 must have one-thousand-nine-hundred-twenty
(1920) parallel paths.
The function of the image independent function shift register 614 is
to receive from the controller 622 the Walsh function values
3 0 corresponding to the first electrodes serviced by the processing system
510
for each time slot T. Having received the Walsh function values for the
time slot T over the image independent function bus 635, the image
independent function shift register 614 then transfers the received Walsh
function values for the time slot T to the calculation engine 610 for use in
calculating an image dependent signal for the time slot. The image
independent function shift register 614 also drives the image independent
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output lines 514 at a rate controlled by the controller 622 in accordance
with the preferred embodiment of the present invention with the Walsh
function values corresponding to the first serviced by the processing
system 510 for each time slot T. The image independent function shift
5 register 614 is preferably a conventional two hundred forty by one bit
serial
input/parallel output shift register. The image independent function shift
register 614 is simple enough that it could alternatively be incorporated
into the controller 622, particularly in an embodiment using a high level
of circuit integration.
10 The calculation engine 610 is coupled to the image independent
function shift register 614 by parallel transfer bus 636 for transferring the
Walsh function values to the calculation engine 610. The parallel transfer
busses 636 must be sufficiently wide to transfer a one-bit Walsh function
value for each first electrode serviced by the processing system 510. For
15 example, in the processing system 510 servicing two-hundred-forty first
electrodes, the parallel transfer bus 636 must have two-hundred-forty
parallel paths. It will be appreciated that while Walsh functions are
preferred, other orthonormal functions may be used as well by the
calculation engine 610 to perform the calculations. The calculation engine
2 0 610 computes an image dependent signal having one hundred sixty values
during each of the time slots. Each of the one hundred sixty values is used
to drive one second electrode, and is determined from one line of image
values stored in the frame buffer 608, one correction factor stored in the
correction factor buffer 601, and the Walsh function (image independent
function) for a time slot T. The correction factor is based on the
corresponding one line of image values. Thus the calculation engine 610
makes one hundred sixty line image dependent value calculations during
each time slot, each value dependent on only one line of image values.
The structure and operation of the calculation engine 610 is described in
3 0 greater detail herein below. The controller 622 controls the storage of
each
line of image value into the frame buffer 608 such that the storage of each
line is performed between successive value calculations of two values of
the image dependent signal and never during a line reading operation
portion of a value calculation involving the corresponding line of image
3 5 values, in which the corresponding line of image values is read from the
frame buffer 608. The controller 622 is further coupled to the frame sync
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line 638 and to the clock line 642 for receiving frame sync and clock
signals, respectively, from a source of the frames of data, e.g., a processor
of
a personal computer.
It will be appreciated that image values are stable while the
calculation engine 610 is making an image- dependent value calculation
based on a line of image values, because the image line is stored between
image value calculations. The memory and calculation architecture in
accordance with the preferred embodiment of the present invention
avoids image smearing and loss of contrast which would occur if image
values were being updated in the direction orthogonal to the line
direction. In prior art display systems, in which lines of image values are
received as rows of image values and in which the image dependent
signal is applied orthogonally to the column electrodes of the display, loss
of contrast and smearing are avoided by using two full frame buffers, and
reading from one frame buffer while writing to the second frame buffer.
This is done in prior art display systems to avoid a change of image values
which occurs when only one frame buffer is used in such prior art
systems, due to incompatible "directions" of the lines of image values
being received and the image values being read from the frame buffer to
2 0 compute the image dependent signal values. The unique architecture
described in accordance with the preferred embodiment of the present
invention reduces the video memory requirements essentially to the line
buffer 602 and the frame buffer 608, by storing the image values as a
plurality of the lines in the frame buffer 608 and calculating an image
dependent output signal having values each of which is dependent on
one line of image values. The unique architecture described in accordance
with the preferred embodiment of the present invention, which uses
parallel line input and output for the single frame buffer 608 simplifies the
interconnection of the video memory in comparison to prior art systems
3 0 in which the inputs of the image values to the frame memories are in a ,
direction orthogonal to the outputs of the image values from the frame
memories.
Referring to FIG. 7, an electrical block diagram of a display system 700
in accordance with a first alternate embodiment of the present invention
3 5 comprises a plurality of processing systems 510 coupled to a data input
line
508, preferably eight bits wide, for receiving an input signal including
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successive frames of data to be displayed. The successive frames of data
define image values, which are grouped into lines. The lines are
horizontal scans, or rows of image values, in accordance with the first
alternate embodiment of the present invention. The successive frames of
data include four hundred eighty of the lines, each consisting of six
hundred forty serially transmitted image values. The LCD 701 is fabricated
using conventional display design and fabrication techniques, having six
hundred forty column electrodes, hereafter referred to as first electrodes,
extending vertically across the LCD 701 and two sets of row electrodes,
hereafter referred to as second electrodes. It will be appreciated that the
lines of image values have a horizontal, or row, direction which
corresponds to the second set of electrodes. Each set of second (row)
electrodes extends horizontally from an edge (left or right) almost to the
center of the display 503, each second (row) electrode thereby crossing one
half of the first (column) electrodes. This split second electrode
organization reduces the amount of calculations performed by each
processing system and improves the contrast and maximum frame rate of
the display system 700 in a simple and cost effective manner. To reduce
calculation requirements for each of the processing systems 510 the LCD
2 0 701 has been partitioned into six areas 711, each serviced by one of the
processing systems 510, and each containing one hundred sixty row
electrodes 106 and three hundred twenty column electrodes 104. It will be
appreciated that the Walsh matrix necessary in the preferred embodiment
of the present invention is of size 29 x 29 (512 x512), and therefore the time
slot, T, is 1/512th of a frame period.
The processing systems 510 are coupled by image dependent (row)
output lines 512, preferably eight bits wide, to video digital-to-analog
converters (DACs) 502, similar to the model CXD1178Q DAC
manufactured by Sony Corporation, for converting the digital output
3 0 signals of the processing systems 510 into corresponding analog second
(row) drive signals. The DACs 502 are coupled to second (row) drive
elements 504 of an analog type, such as the model SED1779DOA driver
manufactured by Seiko Epson Corporation, for driving the second (row)
electrodes 106 of the LCD 100 with the analog row drive signals. Two of
3 5 the processing systems 510 are also coupled by first (column) output lines
514 to first (column) drive elements 506 of a digital type, similar to the
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model SED1704 driver also manufactured by Seiko Epson Corporation, for
driving the first (column) electrodes 104 of the left and right partitions of
the LCD 701 with a predetermined set of Walsh function signals. It will be
appreciated that other similar components can be used as well for the
DACs 502, the second (row) drive elements 504, and the first (column)
drive elements 506.
The second (row) and first (column) drive elements 504, 506 receive
and store a batch of drive level information intended for each of the
second (row) and first (column) electrodes 106, 104 for the duration of the
time slot T (FIG. 4). The second (row) and first (column) drive elements
504, 506 then substantially simultaneously apply and maintain the drive
levels for each of the second (row) and first (column) electrodes 104, 106 in
accordance with the received drive level information until a next batch,
e.g., a batch corresponding to the next time slot T, is received by the second
(row) and first (column) drive elements 504, 506. In this manner the
transitions of the drive signals for all the second (row) and first (column)
electrodes 104, 106 occur substantially in synchronism with one another.
It will be appreciated that the same processing system 510 described
above with reference to FIG. 6 is usable for the display system 700, by
2 0 modifying the size of devices and busses used in the processing system
510.
The description remains the same in other aspects. The line buffer 602 is
then a one hundred sixty image values by eight bit buffer, the frame buffer
is then a one hundred sixty line by three hundred twenty image value by
eight bit buffer, and the image independent function shift register 614 is
then a three hundred twenty by one bit shift register. The parallel data bus
630 is then a one hundred sixty times eight, or one thousand two hundred
eighty, bit wide bus, the parallel data bus 630 is then a three hundred
twenty times eight, or two thousand five hundred sixty, bit wide bus, and
the parallel data bus 636 is then a three hundred twenty bit wide bus.
3 0 Similar size changes, which are needed within the rms -correction factor
calculator 632 and the calculation engine 610 in accordance with the first
alternate embodiment of the present invention, are evident in the more
detailed descriptions herein below to one of ordinary skill in the art.
It will be further appreciated that the display system 700 in accordance
with the first alternate embodiment of the present invention may be a
desirable design choice when a large (e.g., four hundred eighty row and six
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hundred forty column) display system is to be provided and the input
signal does not provide and cannot be economically altered to provide
image values in rows, instead of columns. An example is a case in which
- the equipment which produces the serial data signal already exists in large
quantities and cannot be altered economically to produce a signal having
image values in column format. When a smaller display system (e.g., two
hundred forty row by three hundred twenty column) display system is
involved, a split electrode display panel may not be required to achieve a
desired frame rate and contrast ratio, allowing an selection of the first
electrodes as either the row or column electrodes and thereby allowing the
unique architecture described herein in accordance with the preferred and
alternate embodiments of the present invention, in which each value of
the image dependent signal is determined from only one line of image
values and in which the image dependent signal is applied to the set of
display electrodes corresponding to the direction of the lines of input data.
Referring to FIG. 8, an electrical block diagram of the rms correction
factor calculator 632 of the processing system 510 in accordance with the
preferred and alternate embodiments of the present invention comprises
the data input line 508, for receiving an input signal including successive
2 0 frames of data to be displayed, the control bus 624, for controlling the
rms
correction factor calculator 632, and the timing signal 639. For a display
using +1 to represent a fully "off" pixel and -1 to represent a fully "on"
pixel, and using Walsh functions having values of only +1 and -1, the
correction factor for each line of the display is
1
'JN N _ ~ Ii , ~1)
where N is the number of real first electrodes and Ii is tha value for the
ith image value of the line.
3 0 Adjusting for eight-bit pixel values having a range of 0-255, and
assuming there are two-hundred-forty real first electrodes, equation (1)
becomes
1 240 _ aao C I1 _ 127.5 2 2
240 ~ 127.5
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which simplifies to
240 240
1 255 Ii - ~ Ii, (3)
127.5 240 i=1 i=1
5
which simplifies further to
240 240
2 5 5 ~ Ii - ~ Ii
. (4)
1975
10 It is the function of the rms correction factor calculator 632 to
calculate this correction factor for each line from the data arriving over the
data input 508. The calculated rms correction factors, each of which
corresponds to a line of image values, and also to one value of an image
dependent signal (and thus also to one of the second electrodes), are
15 transferred to the correction factor buffer 601 for temporary storage and
subsequent transfer to the calculation engine 610. Within the calculation
engine 610, each rms correction factor is combined with a summation of
products of image an Walsh function values in accordance with
conventional addressing techniques, as described herein below in
20 reference to FIG. 9. The purpose of the rms correction factor is to
eliminate a non-linear term that would otherwise enter into each image
dependent signal value calculation, as can be proven by one of ordinary
skill in the art of conventional active addressed displays.
The rms correction factor calculator 632 further comprises a first
accumulator 710 coupled to the data input line 508 for summing the pixel
values received. The output of the first accumulator 710 is coupled to both
inputs of a first subtracter 712, wherein the minuend input data is first
shifted eight bits to the left to multiply the minuend input data by two-
hundred-fifty-six, thus producing an output value of 2 5 5 ~ I .
3 0 The data input line 508 is also coupled to the input of a first look-up
table element 704 for determining the square of the pixel value. The
output of the first look-up table element 704 is coupled to the input of a
second accumulator 706 for summing the squares of the pixel values. The
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output of the second accumulator 706 is coupled to the subtrahend input
of a second subtracter 708, to which the output of the first subtracter 712 is
coupled at the minuend input for obtaining the difference 255 I - ~ I2.
The output of the second subtracter 708 is coupled to a second look-up
table element 714 for determining the square root value
~K 255 I - ~ Iz . ~ _ ..
The output of the second look-up table element 714 is coupled to an
input of a multiplier element 716. The other input of the multiplier
element 716 is preprogrammed for a constant value K. The value of K
provides for the division factor of 1975 from equation (4), as well as any
other drive level adjustments that may be required for the LCD 100. The
output of the multiplier element 716 is coupled by the first correction
factor signal 607 to the correction factor buffer 601 for storing the
calculated
correction factor. The timing signal 639 is coupled to the first look-up table
element 704 and the accumulators 706, 710 for providing image value
synchronization with the input signal on the data input line 508. The
control bus 624 is coupled to the second look-up table element 714 and the
multiplier element 716 for performing the multiplication operation when
the complete line is received. The control bus 624 is further coupled to the
2 0 first accumulator 706 and the second accumulator 710 for resetting the
accumulated totals after a complete line is received. It will be appreciated
that an arithmetic logic unit or a microcomputer can be substituted for
some or all of the first and second look-up table elements 704, 714 and the
multiplier element 716. It will be further appreciated that a
microcomputer can also replace all the elements of the rms correction
factor calculator 632.
Referring to FIG. 9, an electrical block diagram of one of the
calculation engines 610 of the processing system 510 in accordance with the
preferred and alternate embodiments of the present invention comprises a
3 0 plurality of 8-bit exclusive-OR (XOR) elements 802, 804, 806. The XOR
elements 802, 804, 806 are coupled to the parallel data bus 630 for receiving
pixel values from the frame memory 608 under the control of the
controller 622. The XOR elements 802, 804, 806 are also coupled to the
parallel transfer busses 636 for receiving Walsh function values from the
3 5 image independent function shift register 614, also under the control of
the controller 622. The function of the XOR elements 802, 804, 806 is to
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complement the bits of the pixel values whenever the corresponding
Walsh function value is a logic ONE, and to leave the pixel value
unchanged whenever the corresponding Walsh function value is a logic
ZERO. A value of ONE must be added to each complemented pixel value
(as explained herein below) in order to correctly subtract the pixel value
from a sum being accumulated by the calculation engine 610.
The outputs of the XOR elements 802, 804, 806 are coupled to adder
elements 808, 810, 812, which are coupled to each other, for generating a
sum of the pixel values that have not been complemented by the XOR
elements 802, 804, 806, and for subtracting from the sum the pixel values
that have been complemented. The input of the first adder element 808 is
coupled to the output 822 of a correction factor adjusting system,
comprising elements 816, 818, 820 for adjusting the sign of the correction
factor corresponding to the line being calculated in accordance with the
Walsh function value for the time slot for a virtual first electrode
designated for the correction factor calculations, and for adding the
requisite value of ONE to each of the complemented pixel values. The
output of the last adder element 812 is coupled to a parallel driver 814,
preferably eight bits wide, for driving the image dependent output lines
2 0 512.
A correction factor adjusting system comprises an XOR element 816
coupled to the controller 622 by the second correction factor signal 609 for
receiving the correction factor for the line, as stored previously by the
correction factor buffer 601, and for receiving over the virtual value signal
2 5 656 the value of the Walsh function for the time slot for the virtual
first
electrode. The output of the XOR element 816 is coupled to an input of an
adder element 818. The other input of the adder element 818 is coupled to
the virtual value signal 656. The function of the XOR element 816 and the
adder element 818 so coupled is to cause the sign of the correction factor
3 0 value to be negative whenever the virtual value is a logic ONE, and
positive whenever the virtual value is a logic ZERO. The output of the
adder 818 is coupled to an input of an adder 820. The other input of the
adder 820 is preprogrammed for a constant value _ of one-hundred-twenty
for all time slots except the first, for which the adder 820 is
3 5 preprogrammed for a value of two-hundred-forty. This is accomplished
by shifting the preprogrammed value of one-hundred-twenty by one bit to
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the left whenever the x2 element 824 is enabled at the first time slot by the
timing signal 637 from the controller 622.
The reason for adding the constant values is to accomplish the
requisite addition of ONE to each complemented pixel value. The
predetermined Walsh factors for the two-hundred-forty real first
electrodes have exactly one-hundred-twenty logic ONES in every time slot
except the first time slot, which has two-hundred-forty logic ONEs. This
means that for every time slot except the first there will be one-hundred-
twenty pixel values complemented by the XOR elements 802, 804, 806 of
the calculation engine 610. For the first time slot , all two-hundred-forty
pixel values will be complemented. As indicated herein above, a value of
ONE must be added to each of the complemented pixel values in order to
correctly subtract the pixel values from the sum. The adder 820 and the x2
element 824 accomplish this.
Referring to FIG. 10, an electrical block diagram of the controller 622
of the processing system 510 in accordance with the preferred and alternate
embodiments of the present invention comprises a microprocessor 901
coupled to a read-only memory (ROM) 902 containing operating system
software and a random access memory (RAM) 906 for storing values of
2 0 variables used by the operating system software. The ROM 902 further
contains predetermined Walsh function values 904, e.g., two-hundred-
fifty-six time slot values for each of the two-hundred-forty real first
electrodes 106, plus one virtual first electrode. The ROM 902 also has been
pre-programmed with an assigned frame portion value 912 indicating the
portion, or block, of the frame of data, i.e., the portion 511 of the display,
that the processing system 510 comprising the controller 622 is assigned to
process. The microprocessor 901 is coupled to the processing system 510 by
the control bus 624, the virtual value signal 656, the timing signal 637, the
frame sync signal 638, and the image independent function bus 635 for
3 0 controlling the processing system 510.
Referring to FIG. 11, an electrical block diagram of a personal
computer 1000 in accordance with the preferred and alternate
embodiments of the present invention comprises the display system 500
coupled to a microcomputer 1002 by the data input line 508 for receiving
3 5 frames of data transmitted by the microcomputer 1002. Each frame of data
defines a plurality of successively transmitted lines of image values. The
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display system 500 is further coupled to the microcomputer 1002 by the
frame sync line 638 and the clock line 642 for receiving frame sync and
clock, from the microcomputer 1002. The microcomputer 1002 is coupled
to a keyboard 1004 for receiving input from a user. The microcomputer
1002 is coupled to a radio receiver 1006 for receiving a video image signal
from a radio transmitter and an image memory 1008 for storing a virtual
image. The input signal on input line 508 is derived from a radio signal
received by the radio receiver 1006. Alternatively, the input signal on
input line 508 can be derived from the image memory 1008, the contents
of which are manipulated by a user using the keyboard 1004.
Referring to FIG. 12, a front orthographic view of the personal
computer 1000 in accordance with the preferred and alternate
embodiments of the present invention depicts the display system 500
supported and protected by a housing 1102. The keyboard 1004 is also
depicted. Personal computers, such as the personal computer 1000, often
are constructed as portable, battery-powered units. The display system 500
is particularly advantageous in such battery-powered units, because the
reduced memory requirement of the processing system 510 of the display
system 500 compared to conventional processing systems for actively
2 o addressed displays greatly reduces the size of the electronic circuit, and
also
reduces the power consumption, thus extending the battery life.
System operation is such that when frame sync is received on frame
sync line 638, each controller 622 of the plurality of processing systems 510
determines from the assigned frame portion value 912 which portion, or
2 5 block of the frame of data the processing system 510 that comprises the
controller 622 is assigned to process, corresponding to the block 511 of the
LCD 100. The controller 622 then delays the start of processing by the
corresponding processing system 510 until the frame of data reaches the
assigned block. -
3 0 A method for use in the electronic device 1000 which processes a
input signal to generate an image on an active addressed display 100 is
described herein below, with respect to FIGs. 13-15. For the purpose of
discussing the method of operation of the display system 500 used in the
electronic device, the term "processor" as used herein below refers to one
3 5 of the plurality of processing systems 510, and the term "line" refers to
a
partial or complete line of image values which is within an assigned block
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511, 711 of the frame of data. Thus a line is a partial or complete line of
image values, depending on the configuration of the blocks 511, 711.
Referring to FIG. 13, a flow chart depicting the operation of loading
the video memory 640 in accordance with the preferred and first alternate
5 embodiments of the present invention begins with the controller 622 of
the processor waiting for the-start of the block within a frame of data.
When a start of block is determined, at step 1202, the controller 622
initializes a line counter at step 1205 and a image value counter at step
1210. At step 1215, the next image value is received. The image value is
10 stored into a next location in the line buffer 602 at step 1220. When the
image value is not the last image value in the line at step 1225, the
operation continues at step 1215. When the image value is the last image
value in the line at step 1225, the line is stored in the next line location
in
the frame buffer 608 at step 1230, erasing a corresponding line of image
i5 values stored. therein from the -previous frame of data. The controller 622
controls the storage of the line into the frame buffer 608 at step 1230 so
that
the storage does not take place while the corresponding line of image
values is being read from the frame buffer 608 by the calculation engine
610 at step 1408 (FIG. 15). When the line is not the last line in the block at
2 0 step 1235, the operation continues at step 1210. When the line is the last
line in the block at step 1235, the operation continues at step 1205. In
summary, lines of image values corresponding to a block of lines within a
frame are stored into corresponding locations in the frame buffer memory
608 as they are received. It will be appreciated that controlling the line
2 5 storage at step 1230 to not occur while the corresponding line is being
read
from the frame buffer 608 avoids loss of image contrast and image
smearing.
Referring to FIG. 14, a flow chart depicting the operation of the rms
correction factor calculator 632 in accordance with the preferred
3 0 embodiment of the present invention begins with the controller 622
waiting for the start of the block within a frame of data corresponding to
the area 511 of the LCD 100 assigned to the controller 622. When the start
of the block is determined at step 1302, the first and second accumulator
elements 710, 706 are initialized at step 1304 to zero by the controller 622.
3 5 Next, the first look-up table element 704 squares the image value at step
1310, and the squared image value is then added at step 1314 to the second
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accumulator element 706 to derive ~ I2 . Concurrently, the image value
is added at step 1312 to the first accumulator element 710 to derive ~ I.
When all the image values for the line being calculated have not been
received in step 1316, the operation continues at step 1306 to receive a next
image value.
When all the image values for the line being calculated have been
received, in step 1316, then ~ z is multiplied by two-hundred-fifty-five at
step 1318, as described herein above in the discussion of FIG. 8. Next, E z2
is subtracted at step 1320 from the value obtained at step 1318, the
subtraction being done by the second subtracter element 708. Then the
square root of the value obtained at step 1320 is determined at step 1322 by
the second look-up table element. The value determined at step 1322 is
then multiplied at step 1323 by the constant K in the multiplier element
716. Next, the correction factor value for the line C K 2 5 5 ~ I - E I2, is
transmitted from the rms correction factor calculator 632 to the correction
factor buffer 601 and stored, at step 1324, in the correction factor buffer
601
at the location corresponding to the calculated line.
When, at step 1326, the controller 622 determines that the calculated
line is not the last line assigned to the processing system 510, the
controller
2 0 622 initializes the rms correction factor calculator 632 at step 1304 to
begin
processing the next line of data. When the controller 622 determines that
the calculated line is the last line assigned to the processing system 510,
the
controller 622 waits for the next block to arrive at step 1302.
Referring to FIG. 15, a flow chart depicting the operation of the
2 5 calculation engine 610 in accordance with the preferred embodiment of
the present invention begins with the controller 622 waiting for a start of
the next frame of data. When the start of the next frame of data is
determined at step 1402, the controller 622 selects a next time slot for
processing and initializes the image independent function shift register
3 0 614 with Walsh function values for the time slot for each of the first
electrodes assigned to the controller 622, plus the virtual electrode, e.g.,
two-hundred-forty-one Walsh function values for the time slot, at step
1404.
At step 1406 the controller 622 then selects a next line for transfer
3 5 from the frame buffer 608 to the calculation engine 610 and selects a
correction factor corresponding to the selected line and transfers the
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correction factor from the correction factor buffer 601 to the calculation
engine 610. Next, the controller 622 controls the frame buffer RAM 608 to
transfer in parallel at step 1408 the two hundred forty image values of the
selected line to the calculation engine 610. Concurrently, the calculation
engine 610 receives, at step 1410, from the image independent function
shift register 614 the Walsh function values for the time slot for each of
the first electrodes assigned to the controller 622. The calculation engine
610 adjusts the correction factor value at step 1412 in accordance with the
virtual first electrode drive signal for the selected line and the selected
time slot, the adjustment made as described herein above in reference to
FIG. 9.
Next, at step 1414, the calculation engine 610 derives an image
dependent output signal by adding together the adjusted correction factor
value and the image values of the selected line corresponding to real first
electrodes having a Walsh function value of ONE, and subtracting from
that sum the image values of the line corresponding to real rows having a
Walsh function value of ZERO. Then at step 1416 the calculation engine
610 and image independent function shift register 614 drive the image
dependent and image independent output lines 512, 514 during the time
2 0 slot with the (calculated) image dependent and (predetermined) image
independent signals, respectively.
It is important to note that the steps 1406, 1408, 1410, 1412, and 1414
are preferably performed substantially simultaneously and in parallel to
achieve optimum calculation speed. Also, as was discussed herein above
in reference to FIG. 5, in the preferred embodiment of the present
invention only two of the processing systems 510 are used to drive the first
drive elements 506. It will be appreciated that even a single processing
system 510 is sufficient to drive the first drive elements 506, because the
image independent signals for corresponding first electrodes in each of the
3 0 group of two-hundred-forty first electrodes in the top and bottom halves
of the LCD 100 are predetermined.
In step 1418 the controller 622 checks whether the last line has been
processed for the selected time slot. When the last line has not been
processed for the selected time slot, the flow returns to step 1406 to select
3 5 and process a next line. When the last column has been processed for the
selected time slot at step 1418, the controller 622 checks at step 1422
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whether the last time slot for the frame of data has been processed. When
the last time slot for the frame has not been processed, the operation
continues at step 1404, where the controller 622 selects a next time slot for
processing. When the last time slot for the frame of data has been
processed at step 1422, operation continues at step 1402, where the
controller 622 will wait to start processing a next frame of data.
Thus, in the preferred and first alternate embodiments of the present
invention, the video memory consists essentially of a single line buffer
and a single frame buffer. Other logic may be needed in the video
memory for such functions as input and output, but no significant
additional image value memory is required. An insignificant amount of
additional memory, such as storage for one image value, may be in the
video memory of the preferred and first alternative embodiments of the
present invention, for example, to simplify the buffering of one image
value.
The preceding discussion and analysis of the preferred embodiment
of the present invention applies to image values represented by eight-bit
data. It will be appreciated that the present invention can be adjusted to
accommodate image values represented by both larger and smaller
numbers of bits, e.g., sixteen-bit or four-bit image values.
Thus, the preferred and alternate embodiments of the present
invention provide a method and apparatus for driving an actively
addressed display in a manner that advantageously minimizes the
memory size and power consumption of the required calculation engine.
2 5 By calculating each value of the of image dependent signal based on one
line of image values and driving the second electrodes with the image
dependent signal, the preferred and alternate embodiments of the of the
present invention substantially reduce the amount of image value
memory required, simplify the memory interconnections required, reduce
3 0 the required calculation speed, and thus substantially reduce the power
required to perform the calculations. The reduced memory size and
power compared to conventional display processors for actively addressed
displays is a particularly important advantage in portable, battery-powered
applications, such as laptop computers, in which size and long battery life
35 are highly desirable features.
What is claimed is:
