Electronic digital logic circuitry – Multifunctional or programmable – Array
Reexamination Certificate
2001-08-07
2003-12-16
Le, Don (Department: 2819)
Electronic digital logic circuitry
Multifunctional or programmable
Array
C326S038000, C326S010000
Reexamination Certificate
active
06664808
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to programmable logic devices, and more particularly to a method for using programmable logic devices that contain minor defects.
BACKGROUND OF THE INVENTION
A programmable logic device, such as a field programmable gate array (FPGA), is designed to be user-programmable so that users can implement logic designs of their choices. In a typical architecture, an FPGA includes an array of configurable logic blocks (CLBs) surrounded by programmable input/output blocks (IOBs). The CLBs and IOBs are interconnected by a hierarchy of programmable routing resources. These CLBs, IOBs, and programmable routing resources are customized by loading a configuration bitstream into configuration memory cells of the FPGA. Additional resources, such as multipliers and memory, may be included.
There are strong customer demands for FPGAs that have a large number of CLBs, IOBs, and/or other resources (e.g., multipliers and block RAMs). This is because end products are becoming more complex, which require more CLBs and IOBs to implement complicated designs. As a result, the size of FPGA die and the resources fabricated on the die grow. This means that the chance of finding a defect in a die increases because the number of defects is proportional to the area of a die and the complexity of technology.
The circuits implemented by different customers of FPGAs are unique. Further, a circuit design may undergo modifications during product development phase. Thus, multiple versions of a circuit may be implemented on a FPGA. In other words, FPGAs are not design specific because they can be theoretically used in any design. This situation places a heavy burden on the quality and reliability of the FPGAs. If a FPGA contains a single defect (e.g., one of its configuration memory cells is defective), it may render an end product unusable because the design may need to use that defective resource. In order to avoid problems with customers, a FPGA manufacturer needs to discard a FPGA even if it contains only one defect.
The problem of low yield has significant economic impact on FPGA manufacturers. There are two types of defects: gross defect (that causes failure of an entire FPGA) and localized defect (that causes failure of small circuitry in the FPGA). It has been found that close to two thirds of large FPGA dies are discarded because of localized defects. If a method can be found to use some of these defective dies, the cost of product of the FPGA manufacturer could be reduced significantly. As a result, customers can take advantage of lower priced FPGAs for specific design patterns.
SUMMERY OF THE INVENTION
The present invention is a method for using a FPGA that contains at least one localized defect. A design is loaded into the FPGA. The FPGA is tested to determine whether it can execute the design accurately even with the localized defect. For example, if the design does not use the localized defect, the localized defect would not affect the execution of the design. In this case, the FPGA is accepted as suitable for this design. Even if the FPGA is found to be unsuitable for a specific design pattern, it may still be suitable for other designs. Thus, in another embodiment of the present invention, additional loading and testing of designs are performed.
By using this method, a FPGA manufacturer can sell FPGAs that are normally discarded. As a result, the price of these FPGAs could be very low.
The present invention is useful for FPGA customers that have finalized their designs. At that time, the design is fixed, and the above mentioned method can be used to determine whether a FPGA with localized defects can be used to implement the design. This method is especially useful for FGPA customers that are considering whether to convert a finalized design from FPGA to an application specific integrated circuit (ASIC). The FPGAs selected in accordance with the present invention can be very price competitive with ASICs. Further, no conversion from one type of device (FPGA) to another type (ASIC) is needed. This means that the “customer specific” integrated circuits are timing and functionality equivalent to the integrated circuits used in product development phase. Thus, it opens another possibility to the customers.
The above summary of the present invention is not intended to describe each disclosed embodiment of the present invention. The figures and detailed description that follow provide additional example embodiments and aspects of the present invention.
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Cho Jae
Davis Shelly G.
Johnson Clay S.
Ling Zhi-Min
Wells Robert W.
Chan H. C.
Kanzaki Kim
Le Don
Xilinx , Inc.
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