Static information storage and retrieval – Read/write circuit – Differential sensing
Reexamination Certificate
2003-04-02
2004-10-26
Le, Thong (Department: 2818)
Static information storage and retrieval
Read/write circuit
Differential sensing
C365S215000
Reexamination Certificate
active
06809977
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is related generally to memory cells, and, more particularly, to memory cell arrays used in display systems.
BACKGROUND OF THE INVENTION
In current memory cell arrays, memory cells in a row of the array are connected to a single wordline for activating the memory cells. For example, in a typical Dynamic Random Access memory (DRAM) cell array as illustrated in
FIG. 1
, DRAM cells of row
110
are connected to and activated by wordline
112
. A critical constraint on this type of design is that, regardless of the user's intention, the wordline activates all memory cells of the row simultaneously for writing the intended memory cells during a writing cycle. Consequently, the timing of write events is highly correlated. This time-correlation may cause artifacts, such as dynamic-false-contouring (DFC) in display systems that employ memory cell arrays for controlling the pixels of the display systems and pulse-width-modulation (PWM) technique for displaying gray-scales of images.
As a way of example,
FIGS. 2
a
to
2
d
illustrate the formation of DFC artifacts in the boundary of two neighboring pixels that are controlled by two neighboring memory cells sharing one wordline. Referring to
FIG. 2
a
, pixels
351
and
353
are two neighboring pixels of the display system and are controlled by two neighboring memory cell, such as memory cells
113
and
115
in FIG.
1
. Assuming that gray-scaled images of an object traversing from left to right are to be displayed by the two pixels, illumination intensities of the two pixels are modulated using PWM waveforms such that, in the screen (pixel) coordinate, the averaged illumination intensity over a frame duration T of each pixel corresponds to the desired grayscale of the image. As viewed by stationary human eyes, the difference of the averaged illumination intensity at the boundary of the two pixels is perceived as the contour of the object, as shown in
FIG. 2
b.
However, the contour of the object will be distorted in the retina coordinate in viewer's eye when the eyes move with the object.
FIG. 2
c
presents the two pixels in the retina coordinate that moves with the eyes and the object. As can be seen, the pixels are distorted. The boundary of the two pixels is extended into a region, in which the averaged illumination intensity varies with position, as shown in
FIG. 2
d
. This variation of the averaged illumination intensity will be perceived and recognized by the eyes as “real” contour of the object. This phenomenon is generally referred to as DFC artifact.
Therefore, methods and apparatus are desired for decorrelating the memory cells and associated pixels of a spatial light modulator such that the DFC like artifacts can be effectively reduced, if not removable.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention provides a method for operating memory cells in each row of the memory cell arrays such that the update events of neighboring memory cells are decorrelated in time. The pixels corresponding to the memory cells are also time-decorrelated thereby. As a benefit of the present invention, stored voltage states of the memory cells of the memory cell array can be read.
In an embodiment of the invention, a method is disclosed herein. The method comprises: providing a memory-cell array comprising a plurality of memory cells; and activating the memory cells of a row of the array using a plurality of separate word lines of the row such that at least two memory cells of the row are activated by separate word lines.
In another embodiment of the invention, a method for displaying a gray-scale image is disclosed herein. The method comprises: providing a spatial light modulator comprising an array of pixel elements; defining at least a first and a second waveform format based on a pulse-width-modulation technique; defining at least a first set of waveforms according to the first waveform format and the gray scale of the image; defining at least a second set of waveforms according to at least the second waveform format; updating the pixels of a row of the array in accordance with a plurality of waveforms that are selected from the first and second sets of waveforms such that at least a first pixel of the row is written in accordance with at least a first waveform selected from the first set of waveforms, and at least a second pixel other than the first pixel of the row is written in accordance with at least a second waveform selected from the second set of waveforms.
In yet another embodiment of the invention, a system is provided herein. The system comprises: a memory-cell array comprising a plurality of memory cells; and a plurality of word-lines coupled to the memory cells of a row of the memory-cell array for selectively activating the memory cells such that at least two memory cells of the row are coupled to separate word-lines of the plurality of word-lines.
In a further embodiment of the invention, a display system for displaying a gray-scale image on a target is proved herein. The display system comprises: a light source; a spatial light modulator that employs a pulse-width-modulation technique for displaying the image by reflecting a beam of incident light from the light source and selectively directing the reflected light to the target, the spatial light modulator further comprising: a plurality of micromirrors for selectively reflecting the beam of incident light onto the target; a memory-cell array having a plurality of memory cells for storing a set of information for controlling the deflections of the micromirrors; and a plurality of word lines coupled with the memory cells of a row of the memory-cell array for activating the memory cells for updating the stored information such that at least two different memory cells of the row can be actuated by separate word lines of the plurality of word lines.
In still a further embodiment of the invention, a method for displaying a gray-scale image on a target is disclosed herein. The method comprises: defining a set of separate waveforms in accordance with at least a gray-scale information of the image and based on a pulse-width-modulation technique; directing an incident light onto a micromirror array that has a plurality of deflectable reflective micromirrors; and selectively reflecting, by the micromirror array, the incident light onto the target according to the set of separate waveforms such that at least two different micromirrors of a row of the array reflect the incident light according to at least two separate waveforms.
In yet another embodiment of the invention, a method for displaying an image is disclosed herein. The method comprises: providing a spatial light modulator having rows and columns of pixels in an array; addressing pixels within a row of the array by providing a brightness level to each pixel in the row, the brightness level being achieved by activating each pixel with a series of bits of varying different lengths, wherein the combination of “on” bits during a frame corresponds to a brightness level for each pixel; and wherein the order of the series of bits for each pixel in a row is not the same or the weightings of the series of bits are different.
In still yet another embodiment of the invention, a method for displaying an image is disclosed herein. The method comprises: providing a spatial light modulator having rows and columns of pixels in an array; addressing pixels within a row of the array by providing a brightness level to each pixel in the row, the brightness level being achieved by activating each pixel with a series of bits of different lengths, wherein a plurality of pixels in the row have the same brightness level but a different combination of “on” and “off” bits during a frame.
In yet another embodiment of the invention, a spatial light modulator is provided herein. The spatial light modulator comprises: a plurality of rows and columns of pixels in an array; a bit line for each column; and a plurality of word lines for a row of the plurality of rows.
Le Thong
Muir Gregory R.
Reflectivity, INC
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