Color LCD driver with a YUV to RGB converter

YUV to RGB converter for converting a digital YUV signal having a Y signal, a U signal, and a V signal to a digital RGB signal having an R signal, a G signal, and a B signal according to equations: EQU R=Y+N.sub.1 .times.V EQU G=Y-N.sub.2 .times.V-N.sub.3 .times.U EQU B=Y+N.sub.4 .times.U PA1 wherein the YUV to RGB converter performs only bit shifting and adding/subtracting operations, and N.sub.1, N.sub.2, N.sub.3, and N.sub.4 are constants.

This application claims the benefit of Korean patent application No. 
36841/1997, filed Aug. 1, 1997, which is hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a color liquid crystal display (LCD) 
driver, and more particularly, to an improved color LCD driver with a YUV 
to RGB converter for converting data signals of a YUV type to data signals 
of a digital RGB type when an LCD controller transmits the data signals as 
the YUV type. 
2. Discussion of the Related Art 
The present invention relates to a number of methods for displaying a 
digital color image represented in a variety of methods, such as an RGB 
method for color computer graphics or a color TV, a YUV method for a 
broadcast system, a YIQ or YCrCb method, and a CMYK method for a color 
printer. The RGB method displays color using data signals of R (red), 
G(green), and B(blue). However, the YUV type displays color with a single 
Y signal (a luminance element), and U and V signals, which are chrominance 
elements. 
As shown in FIG. 1, a conventional color LCD driver converts data signals 
of a digital RGB type outputted from an external LCD controller (not 
shown) into analog data signals, and then transmits the analog data 
signals to an LCD. The LCD driver comprises control logic 10 for 
outputting control signals which control input registers 20 in response to 
a control signal 20 received from the external LCD controller; the input 
registers 20 for sequentially storing the RGB data signals outputted from 
the external LCD controller according to the control signals outputted 
from the control logic 10; storage registers 30 for receiving and storing 
the RGB data signals stored in the input registers 20; a register string 
40, wherein a plurality of resistances are connected serially, for 
selecting 64 points of the resistance having a desired voltage, thereby 
outputting voltage signals V0-V63 with 64 different levels in response to 
9 voltage signals V0-V8 received from an external power supply; and a 
digital to analog converter (D/A converter) 50 for converting the digital 
RGB data signals stored in the storage registers 30 to analog data signals 
and then outputting the analog data signals to a column of an LCD panel 
(not shown) according to the 64 voltage signals outputted from the 
register string 40. 
A data bus connected to an internal or external color LCD driver has a 
number of lines depending on the number of data bits corresponding to 
respective digital RGB data signals. That is, a data bus of 6 bits each 
for R (red), G (green), and B (blue), or 18 bits in total, is required to 
display 64 gray levels, and 8 bits each of R, G, and B, or 24 bits in 
total, are required to display 256 gray levels. 
The operation of a conventional converter will now be described. 
When the control signal and data signals of the RGB type received from the 
external LCD controller are inputted to the LCD driver, the control logic 
10 outputs a control signal controlling the input registers 20 of the LCD 
driver. In response to the control signal outputted from the control logic 
10, the input registers 20 sequentially store the digital RGB data signals 
received from the external LCD controller. After the digital RGB data 
signals are sequentially stored in the input registers 20, the storage 
registers 30 receive the digital RGB data signals and store them. 
The register string 40, however, selects 64 points of a resistance 
producing desired voltage therein, thereby outputting voltage signals 
V0-V63 with 63 different levels in response to 9 voltage signals V0-V8 
outputted from an external power supply. 
Finally, the D/A converter 50 selects a voltage corresponding to the 
digital RGB data signals stored in the storage registers 30 by using the 
64 voltage signals V0-V63 outputted from the register string 40, thereby 
converting the digital RGB data signals stored into analog data signals 
and outputting the analog data signals to the column of the LCD panel. 
The conventional color LCD driver, however, must have a data bus 
corresponding to a number of the data signals of R (red), G (green), and B 
(blue). In other words, a data bus of 6 bits of R (red), G (green), and B 
(blue), or 18 bits total, is required to display 64 gray levels, and a 
data bus of 8 bits each of R, G, and B, or 24 bits total, is required to 
display 256 gray levels. Therefore, the pin count of an IC package 
connected to the data bus is so high that electric wiring becomes 
complicated, and a great deal of EMI (electromagnetic interference) is 
produced. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed to a color LCD driver with a 
YUV to RGB converter that substantially obviates one or more of the 
problems due to the limitations and disadvantages of the related art. 
An object of the present invention is to provide a color LCD driver with a 
YUV to RGB converter that uses only bit shifting and adding/subtracting 
operations. 
Another object of the present invention is to minimize the number of bus 
lines needed for transferring color information between an LCD controller 
and an LCD driver. 
Another object of the present is to reduce electromagnetic interference 
generated by color LCD controller/driver circuitry. 
Additional features and advantages of the present invention will be set 
forth in the description which follows, and will be apparent from the 
description, or may be learned by practice of the invention. The 
objectives and other advantages of the invention will be realized and 
attained by. the structure and process particularly pointed out in the 
written description as well as in the appended claims. 
To achieve these and other advantages and in accordance with the purpose of 
the present invention, as embodied and broadly described, in accordance 
with one aspect of the present invention there is provided a color liquid 
crystal display driver including a control circuit for outputting a 
control signal in response to an liquid crystal display controller, input 
registers for sequentially storing digital RGB data signals in response to 
the control signal, storage registers for receiving and storing the 
digital RGB data signals from the input registers, a register string for 
outputting voltage signals in response to external voltage signals and 
having different voltage levels, a digital to analog converter for 
converting the digital RGB data signals stored in the storage registers to 
analog data signals and outputting the analog data signals, a color liquid 
crystal display driver for driving an liquid crystal display panel, and a 
YUV to RGB converter for converting YUV data signals outputted from the 
liquid crystal display controller to the digital RGB data signals and 
outputting the digital RGB data signals to the input registers. 
In another aspect of the present invention, there is provided a color 
liquid crystal display driver including a YUV to RGB converter for 
converting a digital YUV signal having a Y signal, a U signal, and a V 
signal to a digital RGB signal having an R signal, a G signal, and a B 
signal according to equations: 
EQU R=Y+N.sub.1 .times.V 
EQU G=Y-N.sub.2 .times.V-N.sub.3 .times.U 
EQU B=Y+N.sub.4 .times.U 
wherein the YUV to RGB converter performs only bit shifting and 
adding/subtracting operations, and N.sub.1, N.sub.2, N.sub.3, and N.sub.4 
are constants. 
In another aspect of the present invention, there is provided a color 
liquid crystal display driver including a control circuit for outputting a 
control signal in response to a liquid crystal display controller, input 
registers for sequentially storing digital RGB data signals in response to 
the control signal, storage registers for receiving and storing the 
digital RGB data signals from the input registers, a register string for 
outputting a plurality of voltage signals in response to external voltage 
signals, a digital to analog converter for converting the digital RGB data 
signals stored in the storage registers to analog data signals and 
outputting the analog data signals, a color liquid crystal display driver 
for driving a liquid crystal display panel, a YUV to RGB converter for 
converting YUV data signals outputted from the liquid crystal display 
controller to the digital RGB data signals and outputting the digital RGB 
data signals to the input registers, and a YUV to RGB converter for 
converting a digital YUV signal having a Y signal, a U signal, and a V 
signal to a digital RGB signal having an R signal, a G signal, and a B 
signal according to equations: 
##EQU1## 
wherein the YUV to RGB converter performs only bit shifting and 
adding/subtracting operations. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory and are 
intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION 
Reference will now be made in detail to the preferred embodiments of the 
present invention, examples of which are illustrated in the accompanying 
drawings. 
In the present invention, color data is transmitted by using the YUV 
method, and, in addition, an LCD controller transmits the color data using 
the YUV method, rather than the RGB method. 
Referring to FIG. 2, a color LCD driver includes a control logic 10 for 
outputting a control signal for controlling input registers 20 in response 
to the control signal outputted from an external LCD controller (not 
shown). The color LCD driver includes a YUV to RGB converter 100 for 
converting data signals of the YUV type received from the external LCD 
controller to data signals of the digital RGB type and outputs the data 
signals of the RGB type to the input registers 20. The input registers 20 
sequentially store digital RGB data signals received from the YUV to RGB 
converter 100 according to the control signal outputted from the control 
logic 10. Storage registers 30 for receive and store the digital RGB data 
signals stored in the input registers 20. A register string 40, including 
for example a plurality of resistances connected in serial, selects 64 
points of the resistance to establish desired voltage levels and outputs 
voltage signals V0-V63 with 64 different levels in response to 9 voltage 
signals V0-V8 received from an external power supply. A D/A converter 50 
converts the digital RGB data signals stored in the storage registers 30 
to analog data signals and outputs the analog data signals to a column of 
an LCD panel (not shown) according to the 64 voltage signals outputted 
from the register string 40. 
Referring to FIG. 3, the YUV to RGB converter 100 includes a shifting unit 
110 for shifting U and V signals from an external LCD controller by a 
certain bit number and outputting U1, U2, V1, and V2 signals. The YUV to 
RGB converter also includes an adding/subtracting unit 120 for performing 
adding or subtracting of the U1, U2, V1, and V2 signals and the Y signal, 
thereby converting the YUV type signals to digital data signals of the RGB 
type. 
The shifting unit 110, as shown in FIG. 4, includes a first shifter 111 for 
shifting the U signal by 5 bits, thereby outputting a U1 signal, a second 
shifter 112 for shifting the U signal by 6 bits, thereby outputting a U2 
signal, a third shifter 113 for shifting the V signal by 3 bits, thereby 
outputting a V1 signal, and a fourth shifter 114 for shifting the V signal 
by 6 bits, thereby outputting a V2 signal. Here, the shifting by 5 bits, 6 
bits, 3 bits and 6 bits in the first shifter 111, the second shifter 112, 
the third shifter 113, and the fourth shifter 114, respectively, is 
towards the least significant bit. 
The adding/subtracting unit 120, as shown in FIG. 6, includes a first adder 
121 for adding the V1 signal to itself 11 times and to the Y signal, 
thereby outputting an R (red) signal. The adding/subtracting unit also 
includes a second adder 122 for adding the V2 signal to itself 45 times. 
The adding/subtracting unit also includes a third adder 123 for adding the 
U1 signal to itself 11 times. The adding/subtracting unit also includes a 
fourth adder 124 for adding outputs of the second adder 122 and third 
adder 123. The adding/subtracting unit also includes a subtracter 125 for 
subtracting the output of the fourth adder 124 from the Y signal, thereby 
outputting a G (green) signal. The adding/subtracting unit also includes a 
fifth adder 126 for adding the U2 signal to itself 111 times and to the Y 
signal, thereby outputting a B (blue) signal. 
The operation of the color LCD driver with YUV to RGB converter of the 
present invention will now be described. 
As shown in FIGS. 3 through 6, when a data signal of a YUV type from the 
external LCD controller is transmitted to an LCD driver, the shifting unit 
110 shifts the U signal by 5 and 6 bits, thereby outputting the U1 and U2 
signals, respectively, and shifts the V signal by 3 and 6 bits, thereby 
outputting V1 and V2 signals, respectively. 
Then, the adding/subtracting unit 120 adds the Y, U1, U2, V1, and V2 
signals, and subtracts the U1, U2, V1, and V2 signals form the Y signal, 
thereby outputting data signals of the digital RGB type. 
The process by which the data signals of the YUV type are converted to the 
data signals of the digital RGB type in the YUV to RGB converter 100 will 
now be described in detail. 
The present invention relates to a method for an LCD driver for converting 
data signals of the YUV type to data signals of the digital RGB type when 
the external LCD controller transmits the data signals as the YUV type. 
The data signals of the YUV type can be converted to the digital RGB type 
data using the following equations: 
EQU R=Y+1.375.times.V (1) 
EQU G=Y-0.703125.times.V-0.34375.times.U (2) 
EQU B=Y+1.734375.times.U (3) 
The equations (1), (2), and (3) can be expressed in fractions as follows: 
##EQU2## 
Here, in Formula (1a), the R signal is equal to the V signal divided by 8, 
added to itself 11 times, and then added to the Y signal. In Formula (2b), 
the G signal is equal to subtracting from the Y signal the V signal 
divided by 64 and then added to itself 45 times, and subtracting the U 
signal divided by 32 and then added to itself 11 times. In Formula (3c), 
the B signal is equal to the U signal by 64, added to itself 111 times, 
and then added to the Y signal. The constants 11/8, 45/64, 11/32 and 
111/64 may be referred to as constants N.sub.1, N.sub.2, N.sub.3, and 
N.sub.4, respectively. 
Shifting a binary value by a single bit is equivalent to dividing it by 2, 
shifting a binary value by 3 bits is equivalent to dividing it by 
2.times.2.times.2=8, shifting a binary value by 5 bits is equvalent to 
dividing it by 32, and shifting a binary value by 6 bits is equivalent to 
dividing it by 64. The shifting by 3, 5, and 6 bits in the first to fourth 
shifters 111-114 shown in FIG. 4 is towards the least significant bit 
(LSB). 
In other words, in the shifting unit 110 illustrated in FIG. 4, the first 
shifter 111 shifts the U signal by 5 bits and outputs the U1 signal that 
is equivalent to dividing the U signal by 32, and the second shifter 112 
shifts the U signal by 6 bits and outputs the U2 signal that is equivalent 
to dividing the U signal by 64. The third shifter 113 shifts the V signal 
by 3 bits and outputs the V1 signal that is equivalent to dividing the V 
signal by 8. The fourth shifter 114 shifts the V signal by 6 bits and 
outputs the V2 signal that is equivalent to dividing the V signal by 64. 
As shown in FIGS. 5A to 5C, the first, second, third and fourth shifters 
111-114 shift the inputted data signals toward the least significant bit, 
then output the inputted data signals. FIGS. 5A, 5B, and 5C illustrate the 
third shifter 113 for shifting the inputted data by 3 bits, the first 
shifter 111 for shifting the inputted data by 5 bits, and the second and 
fourth shifters 112 and 114 for shifting the inputted data by 6 bits, 
respectively. In FIGS. 5A, 5B, and 5C, bits that are not connected to 
input terminals are called floating bits and are all tied to a logical 
"0". 
In the adding/subtracting unit 120 shown in FIG. 6, first, the first adder 
121 adds the V1 signal to itself 11 times and then adds the Y signal, 
thereby outputting the R signal. The second adder 122 adds the V2 signal 
outputted from the fourth shifter 114 of the shifting unit 110 to itself 
45 times and outputs it. The third adder 123 adds the U1 signal outputted 
from the first shifter 111 to itself 11 times and outputs it. The fourth 
adder 124 adds together an output from the second adder 122 and an output 
from the third adder 123 and outputs it. Then, the subtracter 125 
subtracts the output of the fourth adder 124 from the Y signal, thereby 
outputting the G signal. 
The fifth adder 126 adds the U2 signal to itself 111 times and to the Y 
signal, thereby outputting the B signal. 
Therefore, the data signals of the YUV type transmitted from the external 
LCD can be converted to the digital RGB type by a simple bit shifting 
operation of the data signals in the shifting unit 110 and an integer 
operation in the adding/subtracting unit 120, rather than by dividing, 
which is a more complex operation. 
The digital data signals of the digital RGB type converted in the YUV to 
RGB converter 100 are stored in the input registers 20, passed through the 
storage registers 30, converted to analog data signals in the D/A 
converter 50, and then transmitted to the external LCD panel. 
When the data signals of the RGB type are transmitted in the conventional 
art, each R, G, and B signal needs 6 or 8 lines of a data bus. In the 
present invention, however, the external LCD controller transmits color 
data signals as the YUV type, rather than the RGB type, so fewer bits are 
needed for the data bus. 
When perceiving color, human vision is sensitive to luminance information, 
but generally insensitive to chrominance information. When the data 
signals are transmitted from the external LCD controller, the luminance 
information uses a data bus having more bits and the chrominance 
information uses a data bus having fewer bits. 
Namely, in the YUV type, the Y signal is the luminance information 
(luminance) and the V signal is the chrominance information (chroma). The 
Y signal is transmitted on a data bus of 4 bits, and the U and V signals 
are transmitted on a data bus of 1 or 2 bits, and 4 bits, respectively. 
Accordingly, when a ratio of Y:U:V=4:1:1 is satisfied, the lowest number of 
data bits needed is 6 bits. When the ratio of Y:U:V=4:2:2 is satisfied, 
the lowest number of data bits needed is 8 bits. When the ratio of 
Y:U:V=4:2:4 or Y:U:V=4:4:2 is satisfied, the lowest number of data bits 
needed is 10 bits. When the ratio of Y:U:V=4:4:4 is satisfied, the lowest 
number of data bits needed is 12 bits. Therefore, even when using a data 
bus having only 6 or 8, 10, and 12 bits, it is possible to transmit all 
the color data signals. 
In addition, the YUV method can use memory more efficiently than the 
digital RGB method, and the number of connections needed for memory or 
other devices is smaller. Since the data signals of the digital RGB and 
the YUV method are both digital, converting between them is 
straightforward. 
As described above, the YUV to RGB converter of the present invention 
converts a data signal of the YUV type into a data signal of the digital 
RGB type. By reducing the number of bits in the data bus between the LCD 
driver and the LCD controller, wiring can be done more easily. Also, 
electromagnetic interference can be reduced when transmitting the data 
signals. 
Accordingly, when,color data signals are transmitted from the external LCD 
controller as the YUV type, the YUV to RGB converter according to the 
present invention converts the data signals of the YUV type to the digital 
RGB type, thereby reducing the pin number of a package as well as 
electromagnetic interference. 
While the invention has been described in detail and with reference to 
specific embodiments thereof,-it will be apparent to those skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof. Thus, it is intended that the 
present invention cover the modifications and variations of this invention 
provided they come within the scope of the appended claims and their 
equivalents.