Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
1999-02-25
2002-09-17
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S141000, C341S100000, C345S098000, C345S205000
Reexamination Certificate
active
06452526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image signal processing circuit which converts a serial image signal into parallel form, performs digital-analog conversion on each parallel image signal, and amplifies and outputs it, and a image display apparatus and an electronic apparatus using the image signal processing circuit. Furthermore, the present invention relates to a method of adjusting the amplitude of an analog image signal which is output from a plurality of digital-analog converters. The image signal in the present invention is handled as being equivalent to a picture signal.
2. Description of the Related Art
For example, when performing liquid-crystal display, as the number of pixels of a display screen increases, the transfer frequency of pixel data increases, and the transfer frequency becomes 40 MHz in SVGA (800×600 pixels) having a standard pixel density, and becomes 65 MHz in XGA (1024×768 pixels) having a high pixel density. Meanwhile, the response frequency of writing to a liquid-crystal element is 7 to 8 MHz when a TFT (Thin Film Transistor) is used as a sampling switch. Therefore, a serial image signal is converted into N parallel signals, and the transfer frequency is lowered by 1/N to a frequency at which response is possible by a TFT (see Japanese Unexamined Patent Publication No. 8-352358, WO97/08677, and WO97/49080).
Here, the serial-parallel conversion of an image signal is called “phase expansion”. As shown schematically in
FIG. 14
, serial input data D has serial image data a
1
, a
2
, . . . which are transferred in accordance with a reference clock CLK of, for example, 40 MHz. In the phase-expansion circuit, image data a
1
, a
2
, . . . are expanded by a shift register and a latch circuit so that its data transfer cycle becomes six times as high as that of the original, and the phase-expanded image signals D
1
, D
2
, . . . D
6
are output in parallel.
The method of
FIG. 14
is called “six-phase expansion” and is used in the case of SVGA having low pixel density. The writing frequency in this case is 6.7 MHz. Meanwhile, in the case of XGA having a high pixel density, 12-phase expansion is used, and the writing frequency at this time is 5.4 MHz.
A liquid-crystal display apparatus using a conventional image signal processing circuit including this phase-expansion circuit is shown in FIG.
15
. In
FIG. 15
, a scanning signal from a scanning circuit
501
and a data signal from a image signal processing circuit
502
are provided to a liquid-crystal panel
500
, causing the liquid-crystal panel
500
to be driven.
The image signal processing circuit
502
comprises a phase-expansion circuit
503
, a polarity-inversion circuit
504
, digital-analog converters (hereinafter abbreviated as D/A converters)
511
to
516
, and operational amplifiers
551
to
556
.
Variable resistors
521
to
526
which adjust the output amplitude of an analog signal output from the D/A converters
511
to
516
are connected to parts of output lines
511
A to
516
A of the D/A converters
511
to
516
, respectively. Also, a bias signal line
505
is connected in common to the negative terminals of the operational amplifiers
551
to
556
, and the output lines
511
A to
516
A of the D/A converters
511
to
516
are respectively connected to the positive terminals.
Gain setting resistors
531
to
536
, and
541
to
546
are connected to the operational amplifiers
551
to
556
, respectively. Of these, the gain setting resistors
541
to
546
are formed of variable resistors.
A case will now be considered in which the same halftone display is performed on the entire screen of the liquid-crystal panel shown in FIG.
15
. The outputs of the operational amplifiers
551
to
556
are connected to the respective signal lines along the vertical direction of the liquid-crystal panel
500
. For this reason, when, for example, a voltage different from those of the operational amplifiers
552
to
556
is output from only the operational amplifier
551
, patterns in the form of longitudinal stripes appear every six lines on the liquid-crystal panel
500
, and the display quality is degraded.
Therefore, in the conventional image signal processing circuit
502
shown in
FIG. 15
, the variable resistors
521
to
526
connected to the D/A converters
511
to
516
and the variable resistors
541
to
546
connected to the operational amplifiers
551
to
556
are each adjusted manually.
In recent years, as the liquid-crystal display screen has become larger, of a higher definition or a color-picture display, the number of pixels tends to increase, and the number of variable resistors shown in
FIG. 15
has increased with the increase in the number of pixels.
For example, in a color display of XGA, the number of variable resistors becomes:
12(number of phase expansions)×3(
R, G, B
)×2(number of variable resistors in one line)=72
Since a number of such variable resistors are required, not only is the cost of parts increased, but also manpower and time are necessary for manual resistance value adjustments. This results in an increased cost of the image signal processing circuit or the liquid-crystal display apparatus. Also, since the adjusted resistance value varies with time, this might cause luminance variations to gradually occur, and improvements must be made from the viewpoint of picture quality.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image signal processing circuit in which the number of variable resistors is decreased to lessen the operation of adjusting the resistance value, thereby resulting in decreased cost, and a image display apparatus and an electronic apparatus using the image signal processing circuit.
Another object of the present invention is to provide an image signal processing circuit in which automatic adjustment of the resistance value is made possible and the occurrence of luminance variation with time can be prevented, and an image display apparatus and an electronic apparatus using the image signal processing circuit.
A further object of the present invention is to provide an image signal processing circuit in which the mounting area of resistors is reduced and further, a S/N ratio can be improved and radiation noise can be reduced, and an image display apparatus and an electronic apparatus using the image signal processing circuit.
Still a further object of the present invention is to provide a method capable of adjusting quickly and accurately the output amplitude of a plurality of digital-analog converters.
An image signal processing circuit in accordance with the present invention provides an image signal processing circuit, comprising:
a serial-parallel converter for converting a serial digital image signal into N parallel digital image signals;
N digital-analog converters for converting the N parallel digital image signals into respective analog image signals;
N amplifiers for amplifying and outputting the analog image signals from the N digital-analog converters, respectively; and
N sets of gain setting resistors, connected to the respective N amplifiers, for setting respective gains of the N amplifiers,
wherein each of the N sets of gain setting resistors includes first and second resistors, and the first and second resistors are formed on a first substrate in the same manufacturing step so that the resistance value of each of the N sets of gain setting resistors need not be adjusted.
In the present invention, the resistance ratio of the first and second resistors which constitute a gain setting resistor is substantially the same for each set without requiring any adjustment. Since the first and second resistors are formed on the same substrate in the same manufacturing step, manufacturing is possible with high accuracy in such a manner as to be dependent upon, for example, mask accuracy during exposure. When the resistance ratio of the first and second resistors of each set is substantially the same, the gain of N am
Kaburagi Chiharu
Kurumisawa Takashi
Sagawa Takahiro
Oliff & Berridg,e PLC
Seiko Epson Corporation
Williams Howard L.
LandOfFree
Video signal processing circuit, video display and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video signal processing circuit, video display and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video signal processing circuit, video display and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2842416