Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-01-04
2001-10-09
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S084000, C345S182000
Reexamination Certificate
active
06300922
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to the field of electronic devices and, more particularly to a driver system and method of operation for a field emission device.
BACKGROUND OF THE INVENTION
A field emission device (FED) comprises a cathode which may be conically shaped or have some other suitable form to provide for a point from which electrons are emitted upon application of an electric field. An anode is placed near the tip of the cathode, but separated from the cathode by a vacuum. A FED array includes field emission devices arranged in a series of columns and rows. Each column and row interface defines a pixel having an associated parasitic capacitance. Current display applications demand thinner, lighter, brighter, and less expensive FED arrays that consume less power.
To activate a pixel, a row driver supplies a voltage to each gate in a row of the FED array. A column driver supplies a voltage signal to each cathode in a column of the FED array. This forms an electric field between each cathode and gate at the pixel of the designated column and row. The magnitude of this electric field across the cathode and gate of each pixel controls the emission of electrons from each cathode of a given pixel. An anode power supply provides a global voltage to each pixel in the FED array, creating another electric field between the anode and the cathode of each pixel. The magnitude of this electric field controls the intensity of the light emitted at each pixel.
Typically, a column driver supplies a pulse-width modulated voltage signal starting at a low state and transitioning to a high state later in the frame of the signal, depending on the brightness desired at each pixel. At the beginning of the next frame of the signal, the signal is returned to a low state. Each state transition from high to low discharges the parasitic capacitance associated with each pixel of the FED array. Thereafter, each state transition from low to high recharges these capacitances. Discharging and recharging the capacitances of the FED array causes undesired power dissipation proportional to the frequency of the column driver output signal, pursuant to the equation P=½CV
2
f.
One effort to minimize the power dissipation of FED arrays employs energy recovery circuits. Another technique supplies an analog voltage signal to each column of the array. However, both of these methods require additional components and complexity. These additional components are expensive and occupy valuable packaging space. The resulting FED array is larger and consumes more power than desired or feasible.
SUMMARY OF THE INVENTION
In accordance with the present invention, a field emission device driver system is provided which substantially eliminates or reduces disadvantages and problems associated with prior driver systems.
In accordance with one embodiment of the present invention, a system for reducing the power dissipation of a load includes a driver circuit coupled to a signal conditioner that receives an input signal and generates an output signal having a series of frames. Each frame comprises a selected one of a corresponding frame of the input signal in forward order and a corresponding frame of the input signal in reverse order, in response to the state of a last time segment of a preceding frame of the output signal.
Another embodiment of the present invention is a method for reducing the power dissipation of a load that includes receiving an input signal and generating an output signal having a series of frames. Each frame comprises a selected one of a corresponding frame of the input signal in forward order and a corresponding frame of the input signal in reverse order, in response to the state of a last time segment of a preceding frame of the output signal.
Technical advantages of the present invention include a driver system that reduces the power dissipation of a capacitively loaded device. In a particular application, a FED array receives via column drivers an input signal that specifies a level of illumination for each pixel in a column. A signal conditioner reduces the frequency of state transitions between frames of the input signal while maintaining the proper duty cycle of each frame of the signal. Due to the reduced number of transitions between frames, parasitic capacitances associated with the display discharge and recharge fewer times as under previous FED driver systems, thereby reducing the power dissipation associated with the FED display.
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patent: 5874932 (1999-02-01), Nagaoka et al.
patent: 5939833 (1999-08-01), Song et al.
patent: 5986640 (1999-11-01), Baldwin et al.
Kumar Srilakshmi
Saras Steven
Texas Instruments Incorporated
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