Note: Descriptions are shown in the official language in which they were submitted.
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Mixed Monochrome and Colour Display Driving Technique
100011 The present invention relates to the field of liquid crystal display
and, particularly,
to the field of multi-mode operation of a liquid crystal display screen.
BACKGROUND OF THE INVENTION
100021 The use of high resolution displays combined with high refresh rates to
provide a
video/animation/graphical user experience can significantly increase the load
on a
handheld's power system. The current result is that end-users are able to
enjoy a highly
graphical experience at the expense of reduced battery life and/or increased
battery mass
and size. High resolution displays with high refresh rates are susceptible to
substantial
power losses due to switching inefficiencies associated with driving many
pixels on a
display at high frequency. For example, 80-90% of power requirements of a
field-
sequential display, excluding backlight illumination, are related to switching
losses
associated when the screen is refreshed at a rate such as 2500 Hz. Field-
sequential display
switching power losses are 5 to 10 times greater than the power losses in
conventional
liquid crystal displays based on colour filters.
100031 Thus, it would be desirable to reduce the switching power loss in a
liquid crystal
display. Also, to provide greater versatility for the user in a
video/animation/graphical
environment, it would be desirable to provide different viewing modes
simultaneously on
the display screen.
SUMMARY OF THE INVENTION
100041 This invention addresses the problem of reducing the switching losses
and,
therefore, power requirements of a display while maintaining or increasing
visual quality.
100051 Switching losses associated with refreshing the screen at high rates
can be reduced
if the active area of the display can be categorized into regions such that
each region can be
electrically driven differently.
100061 In cases where the active area of a display can be categorized into
regions, this
invention reduces switching losses by driving pixels in each region by an
algorithm that
minimizes power consumption while maintaining optical performance appropriate
to the
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region's category. In this way, dynamic, high-power, high-refresh requirements
can be
isolated to regions containing colour or video, while low power, low refresh
rates are applied
to regions containing static "black and white" or monochrome text.
[00011 In the case of field-sequential displays, the active area may be
categorized into
different regions, such as colour and monochrome regions. Therefore, images
containing
both types of regions can be driven in "Partial Colour Mode." The regions may
be of
different bit colour depths and different refresh rates.
100021 Normally, the field-sequential display is updated at 2500 Hz and
regions driven at this
rate are capable of full colour video at 83 Hz. This dynamic, full colour
capability, however,
is not required to display monochrome text. In monochrome regions, the refresh
rate can be
safely reduced to 250 Hz (possibly 55 Hz) without loss in visual quality. In
fact, visual
quality may be improved if the driving waveforms are optimized to improve
contrast in
monochrome regions to benefit the display of data such as text.
100031 The use of different driving schemes allows total power consumption to
be reduced
depending on the data being displayed while maintaining visual quality. In the
case of field-
sequential display, the switching losses are decreased by a factor of 10
within monochrome
regions and overall power savings are proportional to the percentage of the
active area
categorized as monochrome. Up to 90% of switching losses can be eliminated by
operating
in "Partial Colour Mode" if the monochrome region occupies the entire display
to yield a
display device with power consumption similar to displays that use colour
filters.
[0004] Partial Colour Mode can be implemented by a gate driver and controller
to allow
certain gate lines to be activated less frequently to reduce the refresh rate
on the associated
portions of the display.
[00051 An aspect of the specification provides a method for generating a frame
of an image
on an LCD screen of a handheld wireless communications device having a
plurality of light-
sources. The method comprises: scanning a first region of contiguous lines of
field
sequentially driven liquid crystal pixels to produce a colour region on the
LCD screen, using
a source driver and a gate driver driven at a first frequency; and scanning a
second region of
contiguous lines of field sequentially driven liquid crystal pixels to produce
a monochrome
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region on the LCD screen, using the source driver and the gate driver driven
at a second
frequency less than the first frequency, wherein the colour region is produced
by scanning, in
the frame, the first region a first number of times; and wherein the
monochrome region is
produced by scanning the second region a second number of times such that the
first number
of times is N times the second number of times, such that switching losses in
the colour
region is less than switching losses in the monochrome region; and activating
the light
sources during a portion of the frame.
[00061 N can be a positive integer and can obey a selected one of the
following relationships:
i) N is greater than three; ii) N is between six and sixteen, inclusive: iii)
N is between six and
twelve inclusive; iv) N is equal to six; v) N is equal to eight; and vi) N is
equal to ten.
100071 The method can further comprise scanning a third region of contiguous
lines of field
sequentially driven liquid crystal pixels to produce a second colour region on
the LCD
screen. The second colour region can be performed by scanning in the frame,
the third region
by a third number of times. The third number of times can be the same as the
first number of
times. The third number of times can be different from the first number of
times. The second
colour region can be different from the first colour region. At least one of
the first colour
region, the second colour region and the monochrome region can comprise a bit
rate colour
scheme different from a bit rate colour scheme of at least one other region.
[00081 The method can further comprise leaving at least one line of pixels in
an off state.
100091 The frame can comprise a first portion respective to the first region
and a second
portion respective to the second region; and wherein pixels in each of the
portions are
refreshed at different frame rates.
100101 The monochrome region can be comprised of black and white.
[00111 The method can further comprise the steps of. receiving a source
pattern for the frame
for presenting on the LCD screen, the pattern including at least the first
region and the
second region; receiving a number of lines respective to each region, each of
the lines
including a plurality of pixels; receiving a pulse sequence per region
corresponding to a
desired pattern for that region wherein one of the pulse sequences consumes
less power than
at least one other of the pulse sequences; receiving a light sequence
corresponding to each
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region; scanning each liquid crystal pixel in each line respective to each
region according to
the pulse sequence respective to that region; and activating the light sources
according to the
light sequence respective to each region. The light sources can be comprised
of three separate
colours red, green and blue or cyan, magenta, and yellow. The light sequence
can be
comprised of three sequential parts respective to each colour. Each colour can
be turned on
during all of its respective the part. Each colour can be turned on during a
portion of its the
respective part. The scanning step can comprise scanning one of the regions
before scanning
another of the regions. The pattern can include a third region of contiguous
lines of field
sequentially driven liquid crystal pixels to produce a second colour region on
the LCD
screen, wherein the scanning step comprises simultaneously scanning the first
region and the
third region.
[00121 Scanning the first region of contiguous pixel lines can occur three
times in a frame.
Each of the three times can correspond to a different colour of illumination
light.
[00131 Another aspect of the specification provides a wireless communications
device
comprising: an LCD screen having multiple lines of liquid crystal pixels
arranged in a
matrix; the LCD operable to generate a frame of an image having at least one
colour region
and at least one monochrome region; a source driver and a gate driver for
scanning the pixels
according to a pulse sequence per region corresponding to a desired pattern
for that region,
the source driver and the gate driver driven at a first frequency to produce
the colour region,
and the source driver and the gate driver driven at a second frequency less
than the first
frequency to produce the monochrome region, wherein the colour region is
produced by
scanning, in the frame, the first region a first number of times; and wherein
the monochrome
region is produced by scanning the second region a second number of times such
that the
first number of times is N times the second number of times, such that
switching losses in the
colour region is less than switching losses in the monochrome region; and a
plurality of light
sources operable according to a light sequence corresponding to each region.
[00141 The light sources can include light emitting diodes. A first one of the
light emitting
diodes can emit red light, a second one of the light emitting diodes can emit
green light, and a
third one of the light emitting diodes can emit blue light or a first one can
emit cyan light, a
second one can emit magenta light, and a third one can emit yellow light.
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[00151 The source driver can be loaded with values to drive source lines of a
sequentially
selected row of the pixels by shifting a bit through a shift register to drive
gates in the matrix;
and wherein the sequential selection of rows is accomplished by selectively
loading one shift
register selected from a plurality of shift registers.
[00161 The wireless communications device can further comprise a display
controller for
controlling the display screen and a light source controller for controlling
the light source.
The display controller can control operations of the light source controller.
100171 Each pixel in the one of the regions can be capable of being scanned on
between two
and sixteen times, inclusive, for each time any pixel another of the regions
is scanned.
[00181 The source driver can be loaded with values to drive source lines of a
selected row of
= the pixels. The values can be read from a look up table. Each of the values
for the first region
can be multiple bits in length and each of the values for the second region
can be a single bit
in length. The gate driver can be capable of selecting rows of pixels for
monochrome mode
and selecting other rows of pixels for colour mode. Selection of rows within a
region can be
performed in a sequential manner. Selection of rows in a sequential manner can
be
accomplished by at least one of selectively loading one shift register
selected from a plurality
of shift registers and selectively loading one shift register selected from a
plurality of shift
registers.
BRIEF DESCRIPTION OF THE DRAWINGS
[00191 Embodiments of present invention will now be described by way of
example with
reference to attached figures, wherein:
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FIG. 1 is a block diagram that illustrates pertinent components of a wireless
communications device that communicates within a wireless communication
network
according to the present invention;
FIG. 2 is a more detailed diagram of a preferred wireless communications
device of FIG. 1
according to the present invention;
FIG. 3 illustrates an embodiment of a backlit liquid crystal display of the
present invention;
FIG. 4 illustrates an embodiment of the liquid crystal display and liquid
crystal display
controller of the present invention;
FIG. 5 illustrates a flow chart of a method of the present invention;
FIG. 6 illustrates an exemplary division of a display screen in accordance
with the present
invention;
FIG. 7 illustrates a block diagram of an LCD and LCD controller of an
embodiment;
FIG. 8 illustrates a timing scheme for the light source and the display scans;
FIG. 9 illustrates an embodiment of the relative timing between the light
source and the
LCD;
FIG. 10 illustrates an alternate embodiment of the relative timing between the
light source
and the LCD;
FIG. 11 illustrates a specific embodiment with optional off regions;
FIG. 12 illustrates an embodiment of a section of the gate line driver;
FIG. 13 illustrates a flow chart for scanning the specific embodiment of FIG.
11;
FIG. 14 illustrates a general overview of the method of Figure 13; and
FIG. 15 illustrates further detail of an embodiment of the scanning for one
colour within
one frame.
DETAILED DESCRIPTION
100121 The present invention relates to a method and device, especially a
mobile station
such as a handheld communications device, that practices the method for
reducing power
switching losses in a display. Preferably, the display is a liquid crystal
display and the
light source includes light emitting diodes (LEDs) of different colours. The
liquid crystal
display may be operated at a rate of 30 or more frames per second. The LCD
controller
provides a train of pulses during each frame that may be varied in number or
length or
both. The number of pulses or pulse width of a single pulse may be used to
vary the grey
scale of a pixel. The LEDs of the light source preferably will include red,
green, and blue
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colours. Other colour schemes, such as cyan, magenta, and yellow, are
contemplated by
the present invention. The present invention may be implemented by adapting
the LCD
controller to drive the gate lines differently in a frame. Although the
present invention is
directed to a liquid crystal display per se, the preferred use of the LCD is
in a mobile
station.
100131 FIG. 1 is a block diagram of a communication system 100 that includes a
mobile
station 102 that communicates through a wireless communication network. Mobile
station
102 preferably includes a visual display 112, a keyboard 114, and perhaps one
or more
auxiliary user interfaces (UI) 116, each of which is coupled to a controller
106. Controller
106 is also coupled to radio frequency (RF) transceiver circuitry 108 and an
antenna 110.
100141 Typically, controller 106 is embodied as a central processing unit
(CPU) which
runs operating system software in a memory component (not shown). Controller
106 will
normally control overall operation of mobile station 102, whereas signal
processing
operations associated with communication functions are typically performed in
RF
transceiver circuitry 108. Controller 106 interfaces with device display 112
to display
received information, stored information, user inputs, and the like. Keyboard
114, which
may be a telephone type keypad or full alphanumeric keyboard, is normally
provided for
entering data for storage in mobile station 102, information for transmission
to network, a
telephone number to place a telephone call, commands to be executed on mobile
station
102, and possibly other or different user inputs.
100151 Mobile station 102 sends communication signals to and receives
communication
signals from the wireless network over a wireless link via antenna 110. RF
transceiver
circuitry 108 performs functions similar to those of a base station and a base
station
controller (BSC) (not shown), including for example modulation/demodulation
and
possibly encoding/decoding and encryption/decryption. It is also contemplated
that RF
transceiver circuitry 108 may perform certain functions in addition to those
performed by a
BSC. It will be apparent to those skilled in art that RF transceiver circuitry
108 will be
adapted to particular wireless network or networks in which mobile station 102
is intended
to operate.
100161 Mobile station 102 includes a battery interface (IF) 134 for receiving
one or more
rechargeable batteries 132. Battery 132 provides electrical power to
electrical circuitry in
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mobile station 102, and battery IF 132 provides for a mechanical and
electrical connection
for battery 132. Battery IF 132 is coupled to a regulator 136 which regulates
power to the
device. When mobile station 102 is fully operational, an RF transmitter of RF
transceiver
circuitry 108 is typically keyed or turned on only when it is sending to
network, and is
5 otherwise turned off to conserve resources. Similarly, an RF receiver of RF
transceiver
circuitry 108 is typically periodically turned off to conserve power until it
is needed to
receive signals or information (if at all) during designated time periods.
100171 Mobile station 102 operates using a Subscriber Identity Module (SIM)
140 which is
connected to or inserted in mobile station 102 at a SIM interface (IF) 142.
SIM 140 is one
type of a conventional "smart card" used to identify an end user (or
subscriber) of mobile
station 102 and to personalize the device, among other things. Without SIM
140, the
mobile station terminal is not fully operational for communication through the
wireless
network. By inserting SIM 140 into mobile station 102, an end user can have
access to any
and all of his/her subscribed services. SIM 140 generally includes a processor
and
memory for storing information. Since SIM 140 is coupled to SIM IF 142, it is
coupled to
controller 106 through communication lines 144. In order to identify the
subscriber, SIM
140 contains some user parameters such as an International Mobile Subscriber
Identity
(IMSI). An advantage of using SIM 140 is that end users are not necessarily
bound by any
single physical mobile station. SIM 140 may store additional user information
for the
mobile station as well, including datebook or calendar) information and recent
call
information.
100181 Mobile station 102 may consist of a single unit, such as a data
communication
device, a multiple-function communication device with data and voice
communication
capabilities, a personal digital assistant (PDA) enabled for wireless
communication, or a
computer incorporating an internal modem. Alternatively, mobile station 102
may be a
multiple-module unit comprising a plurality of separate components, including
but in no
way limited to a computer or other device connected to a wireless modem. In
particular,
for example, in the mobile station block diagram of FIG. 1, RF transceiver
circuitry 108
and antenna 110 may be implemented as a radio modem unit that may be inserted
into a
port on a laptop computer. In this case, the laptop computer would include
display 112,
keyboard 114, one or more auxiliary Uls 116, and controller 106 embodied as
the
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computer's CPU. It is also contemplated that a computer or other equipment not
normally
capable of wireless communication may be adapted to connect to and effectively
assume
control of RF transceiver circuitry 108 and antenna 110 of a single-unit
device such as one
of those described above. Such a mobile station 102 may have a more particular
implementation as described later in relation to mobile station 202 of FIG. 2.
(0019] FIG. 2 is a detailed block diagram of a preferred mobile station 202.
Mobile station
202 is preferably a two-way communication device having at least voice and
advanced
data communication capabilities, including the capability to communicate with
other
computer systems. Depending on the functionality provided by mobile station
202, it may
be referred to as a data messaging device, a two-way pager, a cellular
telephone with data
messaging capabilities, a wireless Internet appliance, or a data communication
device (with
or without telephony capabilities). Mobile station 202 may communicate with
any one of a
plurality of fixed transceiver stations 200 within its geographic coverage
area.
100201 Mobile station 202 will normally incorporate a communication subsystem
211,
which includes a receiver, a transmitter, and associated components, such as
one or more
(preferably embedded or internal) antenna elements and, local oscillators
(LOs), and a
processing module such as a digital signal processor (DSP) (all not shown).
Communication subsystem 211 is analogous to RF transceiver circuitry 108 and
antenna
110 shown in FIG. 1. As will be apparent to those skilled in field of
communications,
particular design of communication subsystem 211 depends on the communication
network in which mobile station 202 is intended to operate.
10021] Network access is associated with a subscriber or user of mobile
station 202 and
therefore mobile station 202 requires a Subscriber Identity Module or "SIM"
card 262 to
be inserted in a SIM IF 264 in order to operate in the network. SIM 262
includes those
features described in relation to FIG. 1. Mobile station 202 is a battery-
powered device so
it also includes a battery IF 254 for receiving one or more rechargeable
batteries 256. Such
a battery 256 provides electrical power to most if not all electrical
circuitry in mobile
station 202, and battery IF 254 provides for a mechanical and electrical
connection for it.
The battery IF 254 is coupled to a regulator (not shown) which provides power
V+ to all of
the circuitry.
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100221 Mobile station 202 includes a microprocessor 238 (which is one
implementation of
controller 106 of FIG. 1) which controls overall operation of mobile station
202.
Communication functions, including at least data and voice communications, are
performed through communication subsystem 211. Microprocessor 238 also
interacts with
additional device subsystems such as a display 222, a flash memory 224, a
random access
memory (RAM) 226, auxiliary input/output (1/0) subsystems 228, a serial port
230, a
keyboard 232, a speaker 234, a microphone 236, a short-range communications
subsystem
240, and any other device subsystems generally designated at 242. Some of the
subsystems shown in FIG. 2 perform communication-related functions, whereas
other
subsystems may provide "resident" or on-device functions. Notably, some
subsystems,
such as keyboard 232 and display 222, for example, may be used for both
communication-
related functions, such as entering a text message for transmission over a
communication
network, and device-resident functions such as a calculator or task list.
Operating system
software used by microprocessor 238 is preferably stored in a persistent store
such as flash
memory 224, which may alternatively be a read-only memory (ROM) or similar
storage
element (not shown). Those skilled in the art will appreciate that the
operating system,
specific device applications, or parts thereof, may be temporarily loaded into
a volatile
store such as RAM 226.
100231 Microprocessor 238, in addition to its operating system functions,
preferably
enables execution of software applications on mobile station 202. A
predetermined set of
applications which control basic device operations, including at least data
and voice
coinrmunication applications, will normally be installed on mobile station 202
during its
manufacture. A preferred application that may be loaded onto mobile station
202 may be a
personal information manager (PIM) application having the ability to organize
and manage
data items relating to the user such as, but not limited to, instant messaging
(IM), e-mail,
calendar events, voice mails, appointments, and task items. Naturally, one or
more
memory stores are available on mobile station 202 and SIM 262 to facilitate
storage of
PIM data items and other information.
100241 The PIM application preferably has the ability to send and receive data
items via
the wireless network. In a preferred embodiment, PIM data items are seamlessly
integrated, synchronized, and updated via the wireless network, with the
mobile station
user's corresponding data items stored and/or associated with a host computer
system
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thereby creating a mirrored host computer on mobile station 202 with respect
to such
items. This is especially advantageous where the host computer system is the
mobile
station user's office computer system. Additional applications may also be
loaded onto
mobile station 202 through network 200, an auxiliary I/O subsystem 228, serial
port 230,
short-range communications subsystem 240, or any other suitable subsystem 242,
and
installed by a user in RAM 226 or preferably a non-volatile store (not shown)
for execution
by microprocessor 238. Such flexibility in application installation increases
the
functionality of mobile station 202 and may provide enhanced on-device
functions,
communication-related functions, or both. For example, secure communication
applications may enable electronic commerce functions and other such financial
transactions to be performed using mobile station 202.
100251 In a data communication mode, a received signal such as a text message,
an e-mail
message, or web page download will be processed by communication subsystem 211
and
input to microprocessor 238. Microprocessor 238 will preferably further
process the signal
for output to display 222, to auxiliary I/O device 228 or both as described
further herein
below with reference to Figures 3-7. A user of mobile station 202 may also
compose data
items, such as e-mail messages, for example, using keyboard 232 in conjunction
with
display 222 and possibly auxiliary I/O device 228. Keyboard 232 is preferably
a complete
alphanumeric keyboard and/or telephone-type keypad. These composed items may
be
transmitted over a communication network through communication subsystem 211.
100261 For voice communications, the overall operation of mobii;, 2tation 202
is
substantially similar, except that the received signals would be output to
speaker 234 and
signals for transmission would be generated by microphone 236. Alternative
voice or
audio I/O subsystems, such as a voice message recording subsystem, may also be
implemented on mobile station 202. Although voice or audio signal output is
preferably
accomplished primarily through speaker 234, display 222 may also be used to
provide an
indication of the identity of a calling party, duration of a voice call, or
other voice call
related information, as some examples.
100271 Serial port 230 in FIG. 2 is normally implemented in a personal digital
assistant
(PDA)-type communication device for which synchronization with a user's
desktop
computer is a desirable, albeit optional, component. Serial port 230 enables a
user to set
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preferences through an external device or software application and extends the
capabilities
of mobile station 202 by providing for information or software downloads to
mobile
station 202 other than through a wireless communication network. The alternate
download
path may, for example, be used to load an encryption key onto mobile station
202 through
a direct and thus reliable and trusted connection to thereby provide secure
device
communication.
100281 Short-range communications subsystem 240 of FIG. 2 is an additional
optional
component which provides for communication between mobile station 202 and
different
systems or devices, which need not necessarily be similar devices. For
example,
subsystem 240 may include an infrared device and associated circuits and
components, or a
BluetoothTM communication module to provide for communication with similarly-
enabled
systems and devices. BluetoothTM is a registered trademark of Bluetooth SIG,
Inc.
(0029] In accordance with an embodiment of the invention, mobile station 202
is a multi-
tasking handheld wireless communications device configured for sending and
receiving
data items and for making and receiving voice calls. To provide a user-
friendly
environment to control the operation of mobile station 202, an operating
system resident on
station 202 (not shown) provides a GUI having a main screen and a plurality of
sub-
screens navigable from the main screen.
100301 The liquid crystal display cell 222 is shown in:gieater detail in
Figure 3 in which a
light source formed from multiple LEDs 322, 324, 326 is used as a backlight.
LCD
controller 316 provides a voltage to the common electrode(s) 308 and the
active elements
310 of the active matrix. The active elements are preferably thin film
transistors. The
common electrode(s) 308 and active elements are supported on substrates 306
and 312,
respectively. The LCD preferably contains a brightness enhancing film or layer
304 to
optimize the distribution of light for a viewer. As the preferred liquid
crystal material is
super twisted nematic, polarizers 302 and 314 are used. The LCD controller 316
sets the
pixel grey scale of the LCD. An optional processor 318 may coordinate
synchronization of
the LCD controller 316 with the light source controller 320. Preferably, the
LCD
controller 316 and the processor 318 are integrated into a single device 317,
which may
simply be referred to as an LCD controller having the capability of
controlling a light
source controller 320. The light source may be implemented by using red,
green, and blue
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LEDs 322, 324, 326. In a specific embodiment, four green, four red, and two
blue LEDs
are used to provide full colour and/or black and white display. The LED
controller 320
may sequence the three colours or may simultaneously energized LEDs of all of
the
colours and terminate power to the LEDs simultaneously. Other combinations of
LEDs are
5 contemplated by the present invention. The light guide 328 may have a
tapered block
construction and may have approximately a trapezoidal form to more evenly
distribute the
light into the LCD. The light guide may also have uneven areas 330, 332 that
scatter the
light so as to avoid shadowing effects in the LCD image. Although uneven area
330 is
shown to project out from the surface of the light guide 328 and uneven area
332 is shown
10 to project inward to the surface of the light guide 328, the uneven areas
may be arranged
differently so long as the arrangement effectively scatters the light from the
LEDs 322,
324, 326. The uneven areas may be abraded, molded, corrugated, chemically
etched, or
the like. Preferably, to maximize the utilization of light, the LEDs 322, 324,
326 and the
light guide 328 are partially enclosed by a reflector such that the only
opening is fully
bounded by the light transmissive area of the LCD.
100311 Figure 4 illustrates an embodiment of the LCD controller 402 and LCD
430 for the
method of the present invention. The LED controller may be internally adapted
to provide
a sequence of lights each centered on a specific wavelength according to the
LEDs
energized, followed by light generated simultaneously from all LEDs or at
least two LEDs
generating light centered on two different wavelengths. In Figure 4, in
synchronization
with the LED controller, the `..CD controller 402 creates a grey scale pattern
for each light
centred on a specific wavelength according to column driver 410 (source
driver) and row
selectors 412-422 (gate driver) in a X-Y matrix arrangement. For a red light
pattern, only
pixels selectable by the column driver 410 may be set to a transmissive state
to provide a
desired pattern. Pixels that do not have a red component of light are turned
off. For green
and blue light patterns, similar procedures are followed. When all red, green,
and blue
colours are transmitted through a given pixel, that pixel may have a white or
whitish
appearance because of the blending of the three primary colours perceived by a
viewer.
Advantages in using the light source to determine colours include elimination
of a colour
filter layer, thus enhancing brightness of the display by reducing a light
absorbing layer,
and increasing the resolution as only one pixel is needed to provide full
colour instead of
separate red, green, and blue pixels. The size of a pixel is allowed to
increase while
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resolution is improved; in other words, using the light source and not the LCD
to determine
colour optimizes substrate real estate usage.
100321 The method of the present invention is generally shown in Figure 5.
Although this
embodiment is directed to the division of the LCD screen into monochrome and
colour
regions, other schemes are contemplated such as high bit rate colour, low bit
rate colour,
mono colour, etc. A processor designates certain lines as colour 502 or
monochrome 504.
Remaining lines are considered to be in an off state 506. If the display
screen is
operational in a display mode 508, then all colour lines are scanned 510
before any
monochrome lines are scanned 512. The reason the colour lines are scanned
first is
because they have a clocking scheme that is different than the monochrome
lines. In other
embodiments, monochrome lines may be scanned before colour lines. If the
monochrome
and/or colour lines are to be changed 514, the new configuration is determined
by
repeating steps 502-506. Scanning in a colour region involves a first sweep of
each line in
the region before any of the lines in the colour region are swept a second or
successive
time.
100331 Figure 6 illustrates an embodiment of the general display screen in the
present
invention. The top and bottom regions of the display 602, 612 are turned off.
The
colouration of the off region is dependent upon the characteristics of the
unbiased liquid
crystal material and the orientation of any polarizers. In the exemplary
division of the
display screen, a colour region 604, a monochrome region 606, another colour
region 608,
and another monochrome region 610 are located between the top and bottom off
regions
602, 612. Many other arrangements are clearly possible; however, in the
present
invention, the display screen is basically divided into horizontal bands that
are in one of
three modes: colour, monochrome, or off. For example, the display screen may
be divided
into a monochrome region and an off region, a monochrome region and a colour
region, or
a colour region and an off region.
100341 Figure 7 illustrates a block diagram an embodiment of the LCD
controller elements
and the LCD. The grey level for the pixels is provided through the source
driver 704. A
memory 712 is used to provide image data. The memory may be volatile, such as
random
access memory, or non-volatile, such as read only memory. The image data is
used to
access a bit pattern for providing grey scale or toggling for a pixel through
a lookup table.
CA 02508183 2005-05-24
12
Lookup table A 708 provides a pattern of multiple bits representing or
correlating to a grey
scale value. Preferably, the bits in a pattern number at least six and may be
eight, ten,
twelve, or sixteen in number. Lookup table B 710 provides a single bit or bit
sequence
representing an on or off state for a pixel in a monochrome region or line on
the display
screen. Optionally, an off state value may be provided in which the source
driver will not
bias the liquid crystal display pixel selected by switch (i.e., multiplexer)
706. The gate line
driver operates to sweep each of the two types of scannable regions
separately. That is, the
colour region scan sequence storage element 724 will be accessed and used to
scan the
designated portions of the display screen 702 before or after the monochrome
sequence
storage element 726 is accessed for scanning. The monochrome scan sequence
storage
element 726 is scanned at a rate different than the rate for the colour
sequence storage
element 724. Switch 722 provides the correct sequence to the gate driver 720,
and,
optionally during the remaining time, disables the gate for OFF regions.
100351 Figure 8 illustrates a colour only mode in which either the entire
display screen is
in colour or the non-colour portion of the display screen is in the off state.
In operation,
pixel grey scale is achieved through pulses written to a pixel during
scanning. Each colour
frame 802 is divided into three parts (or fields) 804, 806, 808 for the three
colours in full
colour mode. Each pixel to be illuminated by a specific colour of light
achieves a grey
scale value from a pulse pattern into the source of the thin film transistor
providing charge
to the pixel. The pulse pattern (i.e., colour scans) includes multiple high
and/or low pulses
for each pixel. One pulse is applied to each colour pixel during a scan of the
colour region
that includes the colour pixel. During the colour region scan (or sweep) 832,
the actuai
scanning occupies most of the time allotted 830 for a given colour. It is the
successive
scans of the colour pixels during a frame that establishes a grey scale value.
A smaller
portion of the time allotted in a scan period is idle time 834. During most of
the scan
period, the light source is turned off 814. In alternative embodiments, the
light source may
remain on for most or all of the scan period and/or the actual scanning may
occupy a
different portion of the time allotted for a given colour. Once the final grey
scale value for
a row or line of pixels is fairly well established, the light source (e.g.,
light emitting diode)
is turned on 812. In some embodiments, during the light source turn on time,
the common
electrode of the display is inverted from a first voltage bias level 822 to a
second voltage
bias level 824 to prevent charge buildup in the liquid crystal that would
degrade
performance and damage the display. The inversion of the common electrode
voltage
CA 02508183 2005-05-24
13
occurs for each colour for each frame. Thus, for a red, green, and blue pixel
LCD, the
common electrode voltage is inverted three times. Other inversion modes are
contemplated by the present invention such as line inversion and pixel
inversion. In line
inversion, a given line may be alternately supplied through the source driver
with voltages
from a first set of a polarity and then supplied with voltages from a second
set of a polarity
opposite to that of the first set; that is, a non-inverting pair of voltages
may be applied and
an inverting pair of voltages may later be applied. In pixel inversion,
alternate columns
may be supplied for each row with voltage sets of opposing polarities.
100361 The power savings advantage of the present invention arises from the
reduction of
switching in the monochrome region. Figures 9 and 10 illustrate two
embodiments for a
single frame of the display having both monochrome and colour regions. In
Figure 9, the
monochrome scan 916 occurs in which each pixel is activated once. During the
monochrome scan, one clock pulse is used to set an on or off value for the
monochrome
pixels, resulting in less switching power dissipation. Then, the grey scale
values are
developed 914 by multiple pulses from the gate line driver in which the source
driver is
loaded with new data during the multiple scans corresponding to a single
colour in a field.
During most of the scan time, there is no illumination 906. Toward the end of
the scan, the
light source of the designated colour is turned on 904 while the gate driver
becomes idle
912. Figure 10 represents an alternative embodiment in which the monochrome
and colour
scans 1016, 1014 are the same as in Figure 9, but the light..sourec is
operated at lower
power for a longer period of time 1004, 1 008 with 'a. short LEf) OFF time
1006.
100371 Figure 11 represents a more specific embodiment of the present
invention in which
the display screen is divided into relatively few regions in which pixels are
activated by
source driver 1102 and gate driver 1104. At the top and bottom of the display
screen are
off regions 1108, 1116. At the center of the display screen is a monochrome
region 1112
between two colour regions 1110, 1114. Two output shift registers (e.g.,
serial in/ parallel
out shift registers) A, B, as illustrated in Figure 12, are used for scanning
the two colour
regions. Shift register A 1210 and shift register B 1208 contain
initialization values for the
gate shift register of regions A and B, respectively. They preferably contain
a one-hot
encoding of the starting line number of their respective regions. (As used in
an
embodiment of the invention, one-hot encoding refers to a single active bit
that is shifted
through the shift register such that only one line at a time of pixels is
written to from the
CA 02508183 2005-05-24
14
source driver.) First shift register A 1210 is loaded and then used to sweep
the first colour
region once, then shift register B 1208 is loaded and then used to sweep the
second colour
region once. The shift registers alternate until the number of scans in that
frame have all
been completed. During the colour regions scan time, the clock rate COLOUR
LINE
CLOCK is relatively high. For example, a 10 MHz clock may be used. After the
colour
regions are scanned, the monochrome region is scanned using a slower clock
MONO LINE
CLOCK to enter a binary value into the pixel to cause the pixel to be on or
off. A switch
1228 may be used to transfer either COLOUR LINE CLOCK or MONO LINE CLOCK to
storage elements 1218, 1226 according to the region by the REGION SELECT
signal in
FIG. 7. The storage elements 1218, 1226 may be latches that latch data on the
rising or
falling edges of a clock, D type flip flops, or the like. Counters 1202-1206
are used to hold
the number of lines in each region. In an alternate embodiment, each colour
region is
scanned multiple times before any other colour region is scanned. In another
embodiment,
the monochrome region(s) is scanned before the colour region(s) is scanned.
100381 Figure 14 illustrates an overview of the embodiment of a method of the
present
invention corresponding to the display scanning system of Figure 12. In the
general
method, initialization occurs 1404 (e.g., registers are initialized) and the
three colour fields
are cycled through 1406-1410 through successive scans during a frame. Mono
regions
may be updated during all, some, or a single one of the colour fields.
100391 Figure 13 illustrates a more detailed embodiment of the method of
Figure 14.
Initially, the gate clock is set equal to 1hz'OLOUR LINE CLOCK through switch
1228.
The LOAD SOURCE PATTERN of FIG. 12 is deasserted 1302 to enable the OUTPUT
SHIFT REGISTER to shift its data. The counters 1202-1206 are loaded, the
number of
scannings per colour are loaded, and the colour and monochrome storage
elements 1208-
1210 are loaded 1304. The light source is turned off 1306. Colour region B's
count 1204
is loaded 1308. For each count of the counter, as long as the counter has not
timed out
1310: the gate clock is switched at the COLOUR LINE CLOCK rate 1312, the gate
shift
register is initialized 1314 to start scanning at the beginning of colour
region B 1114 by
using switch A and B (FIG. 12) and asserting LOAD SOURCE PATTERN (FIG. 12),
and
a succession of gate clocks causes each row of colour region B 1114 to receive
a new
source pattern 1507 which is used to load unique lines (rows) in colour region
B 1114 of
the display screen 1316. Then, colour region A's counter is loaded and a
similar process is
CA 02508183 2005-05-24
repeated but for region A 1110 for each count of the counter, as long as the
counter has not
timed out 1320, 1322, 1324, 1326. After the colour regions have been
sufficiently scanned
in order to establish their grey scale values, the light source is turned on
1328, 1330. After
the colour regions have been completely scanned (i.e., the pulse sequence
plane is zero)
5 1332, 1334, the common electrodes polarity is inverted 1346. If it is
determined that the
monochrome region is to be refreshed 1336, a counter is loaded with the number
of lines
count M 1338 in the monochrome region and the monochrome region is scanned
1344
once, if the count is not zero, at a reduced clock rate 1342 that is
determined by dividing
the line clock by the number of scans per field to yield the MONO LINE CLOCK.
The
10 reduced clock rate may be established by other means and may occupy the
idle time
period.
100401 The method of Figure 13 may be entered in a variety of other ways. In
one
embodiment, in normal mode, the serial in/ parallel out shift registers A, B
may be loaded
wit h counts, and then the mode is switched to partial colour. After the first
line is
15 referenced, the gate driver output is disabled. Then, when mono start is
retrieved, the gate
driver output is enabled. The gate clock is slowed. Each line of the
monochrome region is
driven until the end of the monochrome region is reached. The clock is
switched to a fast
gate clock relative to the monochrome region clock rate. Each line of the
colour region B
is driven until the end of colour region B. The output shift register is reset
to SIPO A.
Each line of colour region A is driven until the end of colour region A. Then,
the output
shift register is reset to SIPO B unless the predetermined number of scans to
achieve grey
scale has been performed for the frame. If the predetermined number of scans
has been
reached, then the gate clock is disabled, the light source is turned on, and
the common
electrode is inverted. A determination is made as to whether to resume normal
mode. If
not, then partial colour mode is maintained and the processing begins again by
slowing
down the gate clock. Otherwise, normal mode is assumed in which the fast gate
clock is
used to control the pixel gates of the display and the gate driver output is
disabled until the
first line is ready for data transfer. By illustrative example, if M
represents a monochrome
region scan and BA represents a scan of colour regions B and A, then the
process may be
depicted as: M BA BA BA BA BA BA BA BA BA BA BA BA invert wait - in which the
light is turned on during the last one or last few of the colour region BA
scans, the invert
period, and the wait period.
CA 02508183 2005-05-24
16
100411 Figure 15 illustrates a more detailed embodiment of a scan for a field.
The gate
line driver is shifted once 1504. The load pattern is deasserted 1506. A new
source pattern
is loaded 1507. The source lines on the display matrix are driven 1508. The
line count is
reduced by one 1510. As long as the counter does not expire (e.g., the line
count remains
greater than zero in a count down mode) 1512, scanning resumes at step 1504.
100421 The above-described embodiments of the present application are intended
to be
examples only. Those of skill in the art may effect alterations, modifications
and
variations to the particular embodiments without departing from the scope of
the
application. The invention described herein in the recited claims intends to
cover and
embrace all suitable changes in technology.
