Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-23
2004-11-09
Nguyen, Jimmy H. (Department: 2693)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000, C345S099000
Reexamination Certificate
active
06816143
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of self-repair of matrix accessed integrated electronics systems, and more particularly to matrix display panels with integrated drivers capable of self-diagnostic and repair through the use of redundant driver circuitry.
BACKGROUND OF THE INVENTION
The integration of column drive circuits on a silicon display panel potentially reduces the cost of display systems, but may also reduce the panel fabrication yield substantially. This is the obvious result of the inclusion of sensitive small geometry active circuit elements on the substrate.
One of the advantages of building a reflective active matrix projection display with liquid crystal on silicon is that the drivers can be integrated with the active matrix itself. This should improve performance and reliability, and lower the total system cost. By integrating the digital to analog conversion on the display panel, a purely digital interface can be provided, reducing the burden imposed by traditional analog data inputs with respect to the high data rates that are required for high resolution, high refresh rate and single panel color sequential operation. Therefore it is advantageous in performance and system cost to have digital data inputs on the panel, and integrate any required digital to analog conversion in the column drive circuits.
Of course this adds to the total amount of active circuitry on the panel. In general, this will have a negligible effect on die size: The minimum die size is mostly determined by the size of the active matrix, a border area for sealing the liquid crystal cell and bond pads. Typically, most if not all of the data conversion and drive circuits can coincide with the border sealing area.
However, a large active circuit area may increase the chances for production defects substantially. In the case of active matrix display panel systems, the yield estimate for the large area of the active matrix has to be evaluated differently than the more standard circuit area. See, S. M. Sze, editor, “VLSI Technology”, McGraw-Hill, Tokyo, 1983 (ISBN 0-07-066594), Chapter 14 by W. J. Bertram, “Yield and Reliability”. See also, (Betty Prince: “Semiconductor Memories”, John Wiley & Sons Ltd., Chichester, England, 2nd Edition, 1991, ISBN 0471924652). The pixel circuits in the active matrix are generally less sensitive to defects because they involve relatively few types of components at relatively low density. In addition, some pixel defects are generally acceptable as long as they result in dark point defects in the image. Defects in the data conversion and driver circuitry, however, typically cause one or more rows or columns to fail, a result that is unacceptable. Therefore, when the dense active circuit area for data conversion and drivers increases, the production yield may be adversely affected, which raises the cost.
One way to improve the yield of the data conversion and drive circuits is to make use of the fact that it consists of large numbers of identical circuits. This means that it is possible to provide additional (spare or redundant) drive circuits that can selectively take over the function of a defective drive circuit. See, e.g., U.S. Pat. Nos. 5,465,053, 5,781,171 and 5,555,001, expressly incorporated herein by reference. This technique is somewhat similar to the repair of large memories in standard production industry practice. In the case of memory devices (see also U.S. Pat. No. 5,555,001), the actual circuit repair is performed during factory testing: a faulty circuit is detected during testing, and the functionality of the defective circuit is replaced by a spare circuit by means of programmable circuit fuses. This takes valuable time and the mechanics of the fuse programming may be difficult to implement. In liquid crystal on silicon display devices, the circuitry is covered with an integrated light shield to prevent malfunction due to leakage currents induced in the silicon by the intense projection light. Therefore, standard laser activated fuse programming is difficult to perform. Another reason is that the blowing of a fuse may actually create damage to the die surface that can easily compromise the tight tolerances on the narrow gap of liquid crystal cell on top of it.
The prior art of display panel devices therefore teaches either to minimize the amount of driver circuitry on the device, which is more sensitive to defects than the display pixels themselves, or to provide a circuitry repair scheme which is implemented during the later stages of manufacturing of the device.
SUMMARY OF THE INVENTION
The column drive circuitry for a matrix display consists mostly of a large number of identical circuits, one for every column. By providing at least one spare column driver and a control circuit within each block of drivers, the system can automatically detect and identify faulty column drivers, which are then functionally replaced with a spare driver. Thus, with the addition of a small amount of extra circuitry, the effective yield can be improved.
In one embodiment, the output of the normal column drivers are systematically compared with the output of a spare column driver, to detect flawed normal column drivers, for example during a power on self test or continuously during operation. In the event of detection of an error, the spare column driver substitutes its output for the output of the defective normal column driver. In a second embodiment, the output of each adjacent pair of column drivers are compared for the same input signal. The column driver under test is disconnected from its associated column, while the adjacent, and all “higher” column drivers are switched to be associated with the column of the “lower” adjacent column driver circuit. In the case of a difference, the “higher” column driver is presumed to be operative, and persistently substitutes for the “lower” column. If the column drivers both produce the same output signal (within a specified tolerance), the scan and test circuit proceeds to test the next adjacent pair of column drivers, with all column drivers “lower” than the column driver under test being connected to their associated column. A spare column driver circuit is provided at the “higher” end of the block, so that if one column driver defect is identified, each column is still provided with an operative driver circuit. In this way, a defective column driver per block does not impair overall device functionality.
In essence, the first and second techniques may be expanded to an increased number of spare column drivers per block. In the first instance, the output of each spare column driver circuit must be individually multiplexed to be able to substitute for the output of each of the normal column driver circuits. In the second instance, the simple adjacent neighbor test must be expanded to a neighborhood test for a larger number of column driver circuits. It is also possible to employ both methods simultaneously to provide two or more spare column drivers per block.
The statistical basis for a projected improvement in fabrication yield is that the likelihood of an error in any of the normal column drivers far exceeds the likelihood of an error in the spare column driver and scan and test circuitry. For example, if there are 101 column drivers in a block (100 normal and one spare), and each has the same probability for defect, then the spare driver is only about 1% as likely to be defective as all the other column drivers together. If the additional circuitry overhead for the scan, test and replace is, for example, 5% (with similar defect sensitivity to the driver circuit itself), then the overall improvement in yield will be about 18 times, with respect to column driver defects. As stated above, the wafer area cost is not significant, because this circuitry typically is provided in a wafer region that has a mechanical function as well, and thus the wafer size is not substantially reduced if the circuitry is minimized.
Depending on the defect probabilities, block sizes, and the like, it may be de
Koninklijke Philips Electronics , N.V.
Nguyen Jimmy H.
LandOfFree
Self diagnostic and repair in matrix display panel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Self diagnostic and repair in matrix display panel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self diagnostic and repair in matrix display panel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3326010