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Testing of Programmable Logic Array Cross Point Defects

IP.com Disclosure Number: IPCOM000084938D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Cha, CW: AUTHOR

Abstract

Described is a method to generate a test set that will detect any detectable cross-point defects of a Programmable Logic Array (FLA) without using extra hardware. One of the most likely physical faults in a PLA is crosspoint defects.

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Testing of Programmable Logic Array Cross Point Defects

Described is a method to generate a test set that will detect any detectable cross-point defects of a Programmable Logic Array (FLA) without using extra hardware. One of the most likely physical faults in a PLA is crosspoint defects.

Any PLA consists of two arrays as illustrated in the drawing. Let X(1), X(2),...,X(n) be the input lines to the search array and they feed into a decoder, which consists of a two-bit decoder and/or a one-bit decoder. The outputs of the decoders Y(1), Y(2),...,Y(2n) feed into the search array. They are usually made by metal lines. Let P(1),P(2),...,P(q) be the word lines of the search array and they are usually made by diffusion lines. Those grid points between the metal lines and diffusion lines are called crosspoints.

Any PLA will have specific personalities (devices) on the array. The cross-point defects can be classified into two categories. One defect is a missing device on the cross-point where one is required and the other is an additional device on the cross-point where it is not required.

Similarly for the read array, it has word lines P(1),P(2),...,P(q) and output lines O(1),O(2),...,O(m). No known method has existed so far to detect those cross-point defects without using extra hardware. A method embodied in an algorithm is provided herein to solve this problem. The method is described as follows:

For those missing devices on the cross-point, it is equivalent to the line that feeds into the NOR gate stuck-at-0. Therefore, these faults will be detected by a stuck fault test set, which can be generated by any known algorithm for stuck fault.

For those additional devices, the word line that has the cross-point on it is selected and applies the value on that cross-point, such that it will deselect the word line if there is an additional device on it. Note, for a search array, it is also necessary to deselect all the other word lines that share the same output line as the one selected if there is any. This always can be done for any detectable cross-point defects. In other words, if a test pattern cannot be generated for any cross-point, then there is or is not a device on that cross-point which will not change the output logic of the array. Hence, it is a undetectable or harmless fault. A theoretical proof is as follows:

Without loss of generality, it is assumed that those word lines in the PLA perform NOR-NOR functions. For a cross-point of Y(i) and P(j) of the search array w...