Matsushita Electric Industrial Co., Ltd.

Semiconductor Technology Academic Research Center

Toshinori Hosokawa

Mitsuyasu Ohta

Akira Motohara

Sadami Takeoka

Osamu Ichikawa

Michiaki Muraoka

Hideo Fujiwara

Hiroshi Date

Masayoshi Yoshimura

Toshihiro Hiraoka

Tomoo Inoue

The area of the circuit to be added for easy testability is reduced. Operations contained in a behavioral description are extracted in an operation analyzing unit; when expanding any operation at the time of behavioral synthesis, if the area of the circuit can be reduced to a greater extent when a DFT is applied to the operation before expansion, a parameter indicating that the operation is not to be expanded at the time of behavioral synthesis is generated and DFT information is added to a DFT library. A behavioral synthesis unit, in accordance with the parameter, generates an RTL description without expanding the operation. A DFT unit implements the DFT by referring to the DFT library, and thereafter expands the operation.

Designing of a logic circuit for testability

A design for testability is applied so as to enable significant reduction in test time of an actual integrated circuit. First, an integrated circuit is full-scan designed on a block-by-block basis and test input patterns are generated (S ). Then, one of the blocks to which the design for testability has not been allocated is selected (S ), and a full-scan design is allocated thereto (S ). Test points are inserted into a block that has more than a prescribed number of parallel test input patterns when that block is full-scan designed (YES in S ) (S ).

Method of design for testability, method of design for integrated circuits and integrated circuits

Flip-flops (FFs) to replace with scan FFs are selected for an integrated circuit designed at the gate level in order that the integrated circuit has an n-fold line-up structure. All FFs in an integrated circuit are temporarily selected as FFs to replace with scan FFs Each FF to replace with a scan FF is temporarily selected as a FF to replace with a non-scan flip-flop, and the structure of the integrated circuit is checked if it has an n-folded line-up structure and if so, then the FF is selected as a FF to replace with a non-scan flip-flop. For an integrated circuit designed at the gate level, flip-flops to replace with scan flip-flops are selected in order that the integrated circuit has an n-fold line-up structure, without recognizing load/hold FFs as self-loop structure FF. Thereafter, FFs to replace with scan FFs are selected in such a way as to facilitate testing on load/hold FFs. The present invention guarantees high fault efficiency in identifying FFs to replace with scan FFs and achieves a higher compaction rate than conventional technology.

Method of design for testability, test sequence generation method and semiconductor integrated circuit

A method of design for testability using scan FF identification of this invention eases generation of test sequences as compared with conventional technique. An FF relation graph is generated from an integrated circuit, FFs having self loops are recognized in the FF relation graph, and all FFs are replaced with scan FFs. FFs not having self loops are sorted in accordance with a predetermined evaluation function indicating the degree of relation with difficulty in generating test sequences. For example, a function indicating the degree of relation with a balanced reconvergence structure is used as the evaluation function. In a sort order thus obtained, with regard to each FF not having self loops, it is determined whether or not the integrated circuit has an n-fold line-up structure in assuming the FF is replaced with a non-scan FF, thereby identifying scan FFs.

Method of design for testability for integrated circuits

Test sequences for use in fault testing for an integrated circuit are efficiently generated. The integrated circuit is subjected to timeframe expansion, thereby generating a time expansion model including a combinational circuit. With respect to this time expansion model, a compaction template is generated by compacting one or more primitive templates indicating whether or not a primary input or a pseudo primary input is present in each time. Test patterns are generated with respect to the time expansion model, and the generated test patterns are transformed, with compaction accompanied, into test sequences. The compaction is conducted by substituting the respective test patterns in the compaction template and connecting the resultant compaction templates. In this manner, short test sequences can be efficiently generated without spending much time on the compaction.

Method of generating test sequences

The invention provides a method of design for testability at RTL which can guarantee high fault coverage and a method of test sequence generation for easily generating test sequences for an RTL circuit which is designed to be easily testable by the method of design for testability. In the RTL circuit, scannable registers are selected so that the RTL circuit can attain an easily testable circuit structure such as an acyclic structure. This RTL circuit is timeframe expanded on the basis of a predetermined evaluation function and logically synthesized, so as to generate a timeframe expanded combinational circuit, that is, a gate level timeframe expanded circuit, as a circuit for test sequence generation. For the timeframe expanded combinational circuit, test patterns for multiple stuck-at faults are generated, the test patterns are transformed into test sequences on the basis of data on timeframes including primary inputs and pseudo-primary inputs, and the test sequences are transformed into scanning test sequences in view of a scan shift operation.

Method of design for testability and method of test sequence generation

A semiconductor IC includes a test circuit comprising a logic circuit, a test timing generator, a first register serving as a test signal generation point, and second and third registers serving as test signal observation points. In this test circuit, a target signal transmission path to be tested is selected from a plurality of signal transmission paths in the logic circuit, and the test timing generator outputs a test clock having a cycle according to a delay time of the selected signal transmission path on design to the first to third registers, whereby the first register generates a test signal and the second and third registers observe the test signal. Therefore, the signal transmission paths connecting the test signal generation point and the test signal observation point are tested with high efficiency, whereby more signal transmission paths are tested for delay faults with less number of times the test is executed.

Semiconductor integrated circuit and method for testing the semiconductor integrated circuit

Flip-flops (FFs) to replace with scan FFs are selected for an integrated circuit designed at the gate level in order that the integrated circuit has an n-fold line-up structure. All FFs in an integrated circuit are temporarily selected as FFs to replace with scan FFs. Each FF to replace with a scan FF is temporarily selected as a FF to replace with a non-scan flip-flop, and the structure of the integrated circuit is checked if it has an n-folded line-up structure and if so, then the FF is selected as a FF to replace with a non-scan flip-flop. For an integrated circuit designed at the gate level, flip-flops to replace with scan flip-flops are selected in order that the integrated circuit has an n-fold line-up structure, without recognizing load/hold FFs as self-loop structure FF. Thereafter, FFs to replace with scan FFs are selected in such a way as to facilitate testing on load/hold FFs. The present invention guarantees high fault efficiency in identifying FFs to replace with scan FFs and achieves a higher compaction rate than conventional technology.

Method of design for testability test sequence generation method and semiconductor integrated circuit

The invention provides a method of design for testability in which design of an integrated circuit is modified, at a register transfer level (RTL) with high abstraction than the gate level, so as to be simply testable and in which the area of a test circuit and the number of test patterns can be decreased as compared with those in the conventional method. An integrated circuit which has been designed in an RTL design step is partitioned into blocks each satisfying a previously defined simply testable condition in a partitioning step, so that the integrated circuit can be simply tested after manufacture. The simply testable condition can be that a circuit has an acyclic structure including no feedback loop, that a circuit has an n-fold line-up structure (wherein n is a positive integer), or the like. In the integrated circuit having been partitioned into the blocks in the partitioning step, the design is modified by using multiplexers, isolation controllers and the like in an isolation step so that the respective blocks can be independently tested.

Method of design for testability at RTL and integrated circuit designed by the same

The invention provides a method of design for testability of a fault in a portion difficult to test such as an enable input of a tristate element. With regard to an integrated circuit design by a scan path method, an observation circuit including an EXOR tree having inputs in the number equal to that of tristate elements to be designed for testability and an observation dedicated scan FF is disposed. The enable inputs of the tristate elements are connected with the input terminals of the EXOR tree, and the output terminal of the EXOR tree is connected with the ordinary data input terminal of the observation dedicated scan FF. Furthermore, the observation scan FF is inserted into a scan chain already formed by the scan path method. In this manner, a fault in logic circuits for controlling the enable input of the tristate elements, which are conventionally difficult to be detected, can be observed at an external output pin through the scan chain.

Method of design for testability, method of design for avoiding bus

There is provided a design-for-testability method for path delay faults capable of assuring high fault coverage without any substantial increase in area overhead. In a given integrated circuit, an initial pattern is generated for the path delay fault selected, and logical values set for scan flip-flops in the initial pattern are stored. A transition pattern is generated for the selected path delay fault. It is judged whether or not the integrated circuit contains a scan flip-flop of which logical value set in the initial pattern is contradictory to the logical value set in the transition pattern. In the affirmative, a value holding element, for example a D latch, having a function of once holding an input data, is inserted in the output signal line of the scan flip-flop presenting a contradiction in logical value. This D latch eliminates a contradiction in logical value in the initial and transition patterns, thereby to prevent the generation of a test pattern from meeting with failure. This results in improvements in path delay fault coverage.

Design-for-testability method for path delay faults and test pattern

In a method of generating a test sequence for testing a stuck-at fault supposed in a sequential circuit as a test circuit, the number of flip-flops which can be replaced with scan flip-flops among flip-flops included in the circuit under test is initially specified in the first step. Next, in the second step, there is calculated, for each of the flip-flops included in the circuit under test, the sequential depth of a clock defined as the minimum number of flip-flops that are passed through while the input side from the clock input terminal of the flip-flop is traced until an external input pin is reached. In the third step, flip-flops are identified with scan flip-flops by the number specified in the first step in the order of decreasing sequential depth of a clock, which was calculated in the second step.

Method of generating test sequence and apparatus for generating test

A method for generating a test sequence for a fault in a sequential circuit to provide high fault coverage. In one embodiment (FIG. 1), a circuit state, which a system fails to justify, is stored as an illegal state in a step 107. In a step 103, a target fault is selected. In a step 104, the system performs its fault propagation processing to generate a test sequence and propagate the target fault from a fault location to any external output pin in such a manner that the circuit state does not coincide with the illegal state set stored in the step 107, and judges the success or failure of the sequence generation. In a step 105, the system performs its state initialization processing to generate a test sequence and transfer the state of the circuit from its initial state to a state when the fault was sensitized in such a manner that the circuit state does not coincide with the illegal state set stored in the step 107, and judges the success or failure of the sequence generation. Since the circuit state when the system fails to justify the state is stored as the illegal state so that a circuit state at the time of generating a subsequent test sequence is prevented from coinciding with the illegal state set, the possibility of the successful test sequence generation can be increased and thus the test sequence generation system can achieve high fault coverage.

Test sequence generation method

An apparatus for and method of performing automatic test pattern generation for a digital circuit specified registers when the process of automatic test pattern generation for one or more faults is aborted which allow detection of circuit faults by scanning the specified registers. The scan request count of the specified registers is updated, and registers having a scan request count greater than the scan request count limit are recognized as critical registers. Automatic test pattern generation is performed while regarding the critical registers as scan registers.

Method and apparatus for performing automatic test pattern generation

An efficient method of generating test sequences for sequential circuits is disclosed. This method generates a test sequence for a combinational circuit which includes an object fault, examines memory elements where a resulting state (other than 'don't care') has been set as a result of the fault. This is followed by fault propagation and state justification. In the event that, due to such factors as limitations in computing time, generation of test sequence was aborted during fault propagation or state justification, the states of the memory elements are provided for determining which memory element should be scanned to detect the fault. In another embodiment an assumed fault from previous processing has been propagated to a memory element and, thus, to a pseudo primary input terminal. The results of the previous processing are used to propagate the fault to a primary output terminal or to another memory element and, thus, to another pseudo primary output terminal. Other embodiments of the invention generate tests according to degrees of difficulty in generating a fault of a particular type along various signal paths in the circuit. These include faults propagated to the control input terminals of memory elements. A final embodiment of the invention determines, as a result of prior processing, values which should be set for a tree circuit input in order to set the tree circuit output to a 0 or a 1. Then, during test generation, when selecting the signal line and the signal to be set, the tree data is used to expedite the selection and processing of signal line and value assignments.

Growing community of inventors

Osaka, Japan

Toshinori Hosokawa