1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to a method for routing gamma voltages.
2. Description of the Related Art
A camera converts an image signal into an electrical signal, and a display restores the electrical signal converted by the camera to the original image signal. The display needs correction such that the electrical signal is restored close to the original image signal.
The human eyes have a response characteristic in a log curve shape with respect to incident light, in order to receive brightness of light in a wide range. However, an image sensor mounted in a camera may receive brightness of in a limited dynamic range. A complementary metal oxide semiconductor (CMOS) image sensor may be designed to increase a gain, in order to clearly represent a dark portion. In this case, a saturation phenomenon may occur in some bright portions.
Gamma correction means a function of changing brightness or luminance and is used to correct the nonlinearity of photoelectric conversion characteristics of an image device and the saturation phenomenon of light. A mathematical expression applied to the gamma correction may be represented by a curve, and the curve is called a gamma curve. When a gamma value is set to a high value, a center portion of the gamma curve is lifted, so that the screen becomes brighter. When the gamma value is set to a low value, the center portion of the gamma curve is lowered, so that the screen becomes darker.
The flat panel display may include liquid crystal displays (LCDs) or plasma display panels (PDPs). Recently, flat panel displays using organic light emitting devices (OLEDs) have been developed.
In general, the flat panel display includes six to eight source driver integrated circuits (SDICs). Each of the SDICs includes two gamma buffers configured to buffer gamma voltages.
The gamma buffers may be arranged in a predetermined order during design, according to the levels of gamma voltages or gray levels. The voltages output from the respective gamma buffers are transmitted to a resistor string. The resistor string includes 255 resistors connected in series, for example, and voltages dropped by the respective resistors exhibit characteristics of the gamma curve.
In this case, due to the voltages buffered by the gamma buffers and the resistances of the resistors connected to the gamma buffers so as to operate as loads, power consumptions of the gamma buffers may differ from each other. Since the power consumptions of the gamma buffers are not equal, the heating values or temperatures of the gamma buffers may also differ from each other.
Referring to FIG. 1, each of two source printed circuit boards (S-PCBs) 120 and 130 includes three SDICs. That is, FIG. 1 illustrates six SDICs IC#1 to IC#6 arranged in the two S-PCBs 120 and 130. Referring to FIG. 3, the temperatures of the SDICs IC#1 to IC#6 are 50.5° C., 61.0° C., 51.0° C., 52.0° C., 53.0° C., and 55.6° C., respectively.
Furthermore, each of the SDICs IC#1 to IC#6 includes two gamma buffers. That is, FIG. 1 includes total 12 gamma buffers GB11, GB12, GB21, GB22, GB31, GB32, GB41, GB42, GB51, GB52, GB61, and GB62. Referring to FIG. 4, power consumptions of the gamma buffers GB11 and GB12 to buffer gamma voltages VH255 and VL255 are 11.9 mW and 3.5 mW, respectively, and the sum of the power consumptions is 15.4 mW. Power consumptions of the gamma buffers GB21 and GB22 to buffer gamma voltages VH254 and VL254 are 87.2 mW and 82.7 mW, respectively, and the sum of the power consumptions is 169.8 mW. Power consumptions of the gamma buffers GB31 and GB32 to buffer gamma voltages VH191 and VL191 are 14.0 mW and 10.9 mW, respectively, and the sum of the power consumptions is 24.9 mW. Power consumptions of the gamma buffers GB41 and GB42 to buffer gamma voltages VH127 and VL127 are 11.7 mW and 10.5 mW, respectively, and the sum of the power consumptions is 22.1 mW. Power consumptions of the gamma buffers GB51 and GB52 to buffer gamma voltages VH31 and VL31 are 15.7 mW and 14.4 mW, respectively, and the sum of the power consumptions is 30.1 mW. Power consumptions of the gamma buffers GB61 and GB62 to buffer gamma voltages VH00 and VL00 are 43.5 mW and 42.7 mW, respectively, and the sum of the power consumptions is 86.2 mW.
A center PCB (C-PCB) 110 provides a routing path between the S-PCBs 120 and 130.
Here, VL represents a voltage from the lowest voltage of a gamma voltage to a medium voltage of the gamma voltage, and VH represents a voltage from the medium voltage of the gamma voltage to the highest voltage of the gamma voltage. When the gamma voltage is 12V, VL represents a voltage of 0V to 5.9V, and VH represents a voltage of 6.1V to 12V. For example, VL255 represents 0V, and VL00 represents a voltage 5.9V. Furthermore, VH00 represents 6.1V, and VH255 represents 12V.
Due to the differences in power consumption among the gamma buffers included in the respective SDICs IC#1 to IC#6 as illustrated in FIG. 4, the temperatures of the SDICs IC#2 and IC#6 are higher than the other SDICs as indicated by dotted lines of FIG. 3.
The lifetime and reliability of the flat panel display are decided by the lifetimes and reliabilities of the respective SDICs. When the temperature of a specific SDIC among six or eight SDICs is higher than the other SDICs, the lifetime and reliability of the high-temperature SDIC are inevitably decreased, compared to those of the other SDICs. When a defect occurs in any one of SDICs mounted in a flat panel display, the flat panel display does not operate.
Therefore, in order to improve the lifetime and reliability of the flat panel display, the lifetime and reliability of a specific SDIC must be prevented from being reduced and degraded in comparison with those of the other SDICs.