Coded data generation or conversion – Analog to or from digital conversion – Digital to analog conversion
Reexamination Certificate
2003-08-25
2004-11-16
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Digital to analog conversion
C341S079000, C341S136000, C341S154000
Reexamination Certificate
active
06819277
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates to a method for reducing spikes in a digital-to-analog converter, and more particularly, to a method for setting a digit circuit that corresponds to a predetermined bit of the digital voltage signal with least signal variation closest to an output module for reducing spikes in a digital-to-analog converter.
2. Description of the Prior Art
Liquid display devices (LCD), which are thin, flat panel display devices, can be found in a plethora of electronic goods, ranging from notebook computers and digital cameras to flight avionics and medical diagnostic tools. LCDs offer crisp, high-resolution images, and have the primary advantage of offering relatively low power-consumption rates while still maintaining good color contrast and screen refresh rates. In recent years, the newly developed low-temperature Poly Silicon LCD (LTPS LCD) can directly attach the driving circuit on the glass substrate so that the quantity of the driving circuits can be reduced, the package/material cost can be downsized, and the reliability and compactness of the commercialized products can be significantly increased.
In an electric circuit, the spikes are generally generated from the power source. In U.S. Pat. No. 6,348,783, “DC/DC converter for suppressing effects of spike noise”, Tateishi et al. disclose an AC/DC transformer for erasing spikes. Regarding display systems, for achieving advantages of power saving, integrity, and cost effectiveness, more LCD systems adopt the digital type of input data so that the digital-to-analog converter should be involved in the data driver. Therefore, the quality of the LCD system relies on the transformation process in the digital-to-analog converter. During the transformation process, spikes generated in the digital-to-analog converter are significantly related to the quality of display since the spikes would lead to the unstable displaying and redundant power consumption. Therefore, effective spike reduction in the digital-to-analog converter becomes a crucial topic for display systems. Nowadays, the type of the digital-to-analog converter in the display system includes the R-string digital-to-analog converter (R-string DAC), the C-string digital-to-analog converter (C-string DAC), and the mixed-type digital-to-analog converter. The R-string digital-to-analog converter most seriously suffers from the spikes. Please refer to
FIG. 1
, which is a schematic diagram of an R-string digital-to-analog converter
10
according to the prior art. The digital-to-analog converter
10
is a 3-to-3 R-string digital-to-analog converter
10
for transforming a 6-bit digital voltage signal into an analog voltage signal. As shown in
FIG. 1
, the digital-to-analog converter
10
includes a receiving circuit
12
, six digit circuits
14
-
19
, a reference circuit
20
, and an output module
22
. The receiving circuit
12
is used for receiving the 6-bit digital voltage signal, and for respectively being electrically connected to the six digit circuits
14
-
19
. The reference circuit
20
is used to provide nine different reference voltages for the six digit circuits
14
-
19
. The nine different reference voltages are respectively 0V, 0.5V, 1V, 1.5V, 2V, 2.5V, 3V, 3.5V, and 4V. The six digit circuits
14
-
19
include a first digit circuit
14
to a sixth digit circuit
19
, and the six digit circuits
14
-
19
(the first digit circuit
14
to the sixth digit circuit
19
) respectively correspond to six bits of the digital voltage signal (a first bit to a sixth bit). For example, the first digit circuit
14
corresponds to the first bit of the digital voltage signal. In addition, each digit circuit includes a plurality of transistors. For instance, the fourth digit circuit
17
to the sixth digit circuit
19
(respectively corresponding to the fourth bit to the sixth bit of the digital voltage signal) respectively include sixteen PMOS-transistors or NMOS transistors, and the first digit circuit
14
to the third digit circuit
16
(respectively corresponding to the first bit to the third bit of the digital voltage signal) respectively include eight PMOS transistors or NMOS transistors. When being implemented, the six digit circuits combined with resistors as shown in
FIG. 1
can operate a voltage-separating function and transform the digital voltage signal into an analog voltage signal corresponding to the digital voltage signal. Afterwards, after a related current will flow to the output module
22
, the output module
22
can output the transformed analog voltage signal to a data line. Therefore, the magnitude of the analog voltage signal determines the light intensity of a pixel in a panel. In addition, as shown in
FIG. 1
, the output module
22
further includes a loading resistor
24
, which is an essential element for the digital-to-analog converter
10
, used for impedance matching.
Please continue to refer to FIG.
1
. In the prior-art digital-to-analog converter
10
, the third digit circuit
16
(corresponding to the third bit of the digital voltage signal) is closest to the output module
22
. Actually, according to the prior art, there is no rule to determine which digit circuit should be closet to the output module
22
or farthest from the output module
22
. Please notice that, in the R-string digital-to-analog converter
10
, the composition and arrangement of the PMOS transistors and the NMOS transistors are predetermined and unchangeable. For instance, the fourth digit circuit
17
corresponding to the fourth bit of the digital voltage signal includes eight PMOS transistors and eight NMOS transistors, and the arrangement of the PMOS transistors and the NMOS transistors in the fourth digit circuit
17
should conform to the embodiment shown in FIG.
1
. Please notice that the first digit circuit
14
to the third digit circuit
16
(corresponding to the first bit to the third bit of the digital voltage signal) respectively includes four PMOS transistors and four NMOS transistors, however, the arrangements of the first digit circuit
14
to the third digit circuit
16
are different.
Please refer to
FIG. 2
, which is a simulation diagram of the outputted analog voltage signal of the prior-art R-string digital-to-analog converter
10
shown in FIG.
1
. The horizontal axis represents variation of time, and the vertical axis represents variation of an output voltage. As shown in
FIG. 2
, the value of the analog voltage signal can reflect serious spike interference, and the maximum spike value can reach 3V, which is even larger than the original value of the analog voltage signal. Moreover, the minimum spike value is 0.6V. Therefore, the above-mentioned spike interference may cause unstable displaying detected by bare eyes and significantly redundant power consumption. After detailed analyses for the R-string digital-to-analog converter
10
shown in
FIG. 1
, we found that the spikes mainly come from the loading resistor
24
included in the output module
22
. However, the loading resistor
24
is essential and unchangeable for the digital-to-analog converter
10
. Therefore, we have to find out a new method without modifying the loading resistor
24
to reduce spikes.
SUMMARY OF INVENTION
It is therefore a primary objective of the claimed invention to provide a method for reducing spikes in the digital-to-analog converter to solve the above-mentioned problems.
In the claimed invention, based on the structure of an R-string digital-to-analog converter, we disclose an arrangement to set a digit circuit that corresponds to a predetermined bit of the digital voltage signal with least signal variation closest to an output module for reducing spikes in a digital-to-analog converter. Therefore, we can eliminate unstable displaying and redundant power consumption without the need of additional installation of electric devices.
According to the claimed invention, a method for transforming a digital voltage signal into an analog voltage signal to reduce spikes by utilizing a digital-to-analog convert
Hu Jen-Yi
Sun Wein-Town
Au Optronics Corp.
Hsu Winston
Nguyen John B
Young Brian
LandOfFree
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