This paper presents a practical test point insertion method for scan-based BIST. To apply test point insertion in actual LSIs, especially high performance LSIs, it is important to reduce the delay penalty and the area overhead of the inserted test points. Here efficient test point selection algorithms, which are suitable for utilizing overhead reduction approaches such as restricted cell replacement, test point flip-flops sharing, are proposed to meet the above requirements. The effectiveness of the algorithms is demonstrated by some experiments.

Low overhead test point insertion for scan-based BIST

The problem of test generation for logic circuits is known to be NP-hard, and hence it is very hard to speed up the test generation process due to its backtracking mechanism. The authors present an approach to parallel processing of test generation for logic circuits in a loosely coupled distributed network of general-purpose computers. They analyze the effects of the allocation of target faults to processors, the optimal granularity (grain size of target faults), and the speedup ratio of the multiple-processor system to a single-processor system. To analyze the case in which a test pattern generated for one fault can also be a test pattern for other faults if fault simulation is performed, they introduce a ratio of newly processed faults to target faults and derive the expressions of optimal granularity in cases of both static and dynamic task allocation. They also derive an expression of the speedup of a multiple-processor system in the homogeneous case. The analysis indicates that the speedup approaches N, the number of servers, if the data transfer time per fault and the waiting time per communication are much smaller than the processing time per fault and if the decrease ratio of newly processed faults due to overlapped processing is much smaller than the ratio of newly processed faults. >

Optimal granularity of test generation in a distributed system

A testability measure called conflict, based on conflict analysis in the process of sequential circuit test generation is introduced to guide nonscan design for testability. The testability measure indicates the number of potential conflicts to occur or the number of clock cycles required to detect a fault. A new testability structure is proposed to insert control points by switching the extra inputs to primary inputs, using whichever extra inputs of all control points can be controlled by independent signals. The proposed design for testability approach is economical in delay, area, and pin overheads. The nonscan design for testability method based on the conflict measure can reduce many potential backtracks and make many hard-to-detect faults easy-to-detect; therefore, it can enhance actual testability of the circuit greatly. Extensive experimental results are presented to demonstrate the effectiveness of the method.

Nonscan design for testability for synchronous sequential circuits based on conflict resolution

A semiconductor integrated circuit is provided whose area overhead due to provision of test points is reduced together with the test time period. In a semiconductor integrated circuit having a plurality of observation points in a tested circuit, the plurality of observation points are divided into a preset number of groups. The semiconductor integrated circuit contains at least one compressing circuit to reduce the number of bits of a multi-bit signal and to output the result (a signal of less bits) to an observable element such as an external output element or a flip-flop with a scan function. The semiconductor integrated circuit also has at least two scan chains each of which is made up with a plurality of flip-flop circuits working as shift registers. Further, the two scan chains are interconnected with a single input terminal.

Semiconductor integrated circuit and its analyzing method

A device and a method are used to test integrated circuits, especially P.L.A.s. The possible faults of a circuit to be tested are determined including logic faults caused by the physical structure and relative position of the circuit elements in the integrated logic circuit. On the basis of the faults, a set of test vectors is determined, each fault modifying at least one of the test vectors applied to the circuit to be tested. It is possible to use test vectors which are modified by the greatest number of possible faults. By determining the test vectors on the basis of the faults which are to be detected, the tests can use a small number of vectors while, at the same time, there is certainty that it will be possible to detect all the faults in a given circuit. Advantageously, a hierarchically-organized set of cells is determined with certain cells consisting of small cells. The method and device can be used to test P.L.A.s by using a small number of test vectors, and are applicable to testing integrated circuits and P.L.A.s.

Device and method for the generation of test vectors and testing method for integrated circuits

Some design-for-testability techniques, such as level-sensitive scan design, scan path, and scan/set, reduce test pattern generation of sequential circuits to that of combinational circuits by enhancing the controllability and/or observability of all the memory elements. However, even for combinational circuits, 100 percent test coverage of large-scale circuits is generally very difficult to achieve. This article presents DFT methods aimed at achieving total coverage. Two methods are compared: One, based on testability analysis, involves the addition of test points to improve testability before test pattern generation. The other method employs a test pattern generation algorithm (the FAN algorithm). Results show that 100 percent coverage within the allowed limits is difficult with the former approach. The latter, however, enables us to generate a test pattern for any detectable fault within the allowed time limits, and 100 percent test coverage is possible.

Akira Motohara

Papers

Design for Testability for Complete Test Coverage

Fast test pattern generation using a multiprocessor system

Test generation for sequential circuit based on boolean function manipulation