Test Application Scheme Research Articles

Compression-Friendly Low Power Test Application Based on Scan Slices Reusing

This paper presents a compression-friendly low power test scheme in EDT environment. The proposed approach exploits scan slices reusing to reduce the switching activity during shifting for test scheme based on linear decompressor. To avoid the impact on encoding efficiency from resulting control data, a counter is utilized to generate control signals. Experimental results obtained for some larger ISCAS’89 and ITC’99 benchmark circuits illustrate that the proposed test application scheme can improve significantly the encoding efficiency of linear decompressor.

Access-in-turn test architecture for low-power test application

ABSTRACTThis paper presents a novel access-in-turn test architecture (AIT-TA) for testing of very large scale integrated (VLSI) designs. In the proposed scheme, each scan cell in a chain receives test data from shift-in line in turn while pushing its test response to the shift-out line. It solves the power problem of conventional scan architecture to a great extent and suppresses significantly the switching activity during shift and capture operation with acceptable hardware overhead. Thus, it can help to implement the test at much higher operation frequencies resulting shorter test application time. The proposed test approach enhances the architecture of conventional scan flip-flops and backward compatible with existing test pattern generation and simulation techniques. Experimental results obtained for some larger ISCAS’89 and ITC’99 benchmark circuits illustrate effectiveness of the proposed low-power test application scheme.

Thermal-Aware Small-Delay Defect Testing in Integrated Circuits for Mitigating Overkill

At-speed testing of deep-submicrometer or nano-scale integrated circuits (ICs) consumes excessive power and creates hotspots and temperature gradient in the chip-under-test. The problem worsens for 3-D ICs, where heat dissipation across layers is more unbalanced. These hotspots in a circuit often cause severe degradation of performance and reliability, as a rise in temperature can introduce an extra delay along paths. As a result, the delay of an otherwise fault-free path may exceed the functional clock period. Such thermal emergencies can thus lead to over-detection and undue yield loss during testing. Their effects will be more severe for small-delay defects (SDDs), which target to sensitize the long paths in a circuit. In this paper, we quantify, for the first time, the impact of thermal emergencies on SDDs and provide a solution to mitigate them. The proposed method is based on: 1) a new thermal-aware (TA) path-selection method, 2) a TA test-ordering method, and 3) an effective scan architecture and a test-application scheme. Experimental results on benchmarks demonstrate that the new method can significantly reduce the number of over-detections of SDDs.

A New Unicast-Based Multicast Scheme for Network-on-Chip Router and Interconnect Testing

3D technology for networks-on-chip (NOCs) becomes attractive. It is important to present an effective scheme for 3D stacked NOC router and interconnect testing. A new approach to testing of NOC routers is proposed by classifying the routers. Routers with the same number of input/output ports fall into the same class. Routers of the same class are identical if their tests are the same. A test packet is delivered to all the identical routers by a simple unicast-based multicast scheme. It is found that the depth of the consumption buffer at each router has great impact on the test delivery time because test application and test delivery for router testing cannot be handled concurrently. Test delivery must set a router to operational mode. A mathematical model is presented to evaluate the impact of consumption buffer depth on the test delivery time. A new and simple test application scheme is proposed for interconnect testing. Some interesting extensions are presented for further test time reduction and thermal considerations. Sufficient experimental results are presented by comparison with one previous method. The proposed method works for single stuck-at, transition, even small delay faults at routers, and single bridging faults at physical, consumption and injection channels.

SOC Test Compression Scheme Sharing Free Variables in Embedded Deterministic Test Environment

This paper presents a new SOC test compression scheme in Embedded Deterministic Test (EDT) compression environment. Compressed test data is brought over the TAM from the tester to the cores in SOC and decompressed in the cores. The proposed scheme allows cores tested at the same time to share some test channels. By sharing free variables in these channels across test cubes of different cores decompressed at the same time, high encoding efficiency is achieved. Moreover, no excess control data is required in this scheme. The ability to reuse excess free variables eliminates the need for high precision in matching the number of test channels with the number of care bits for every core. Experimental results obtained for some SOC designs illustrate effectiveness of the proposed test application scheme.

A thermal-driven test application scheme for pre-bond and post-bond scan testing of three-dimensional ICs

The three-dimensional (3-D) technology offers a new solution to the increasing density of integrated circuits (ICs). In this work, we propose novel scan architectures for 3-D IC pre-bond and post-bond testing by considering the interconnection overhead of through-silicon-vias (TSVs). Since hotspots in 3-D ICs often cause performance and reliability issues, we also develop different test ordering schemes for prebond and postbond testing to avoid applying test vectors that could worsen the temperature distribution. Experimental results show that the peak temperature can be lowered by 20% with the 3-D scan tree architecture. When combined with the test ordering scheme, the 3-D scan tree can further reduce peak temperature by over 30%.

EDT Bandwidth Management in SoC Designs

This paper presents preemptive test application schemes for system-on-a-chip (SoC) designs with embedded deterministic test-based compression. The schemes seamlessly combine new test data reduction techniques with test scheduling algorithms and novel test access mechanisms devised for both input and output sides. In particular, they allow cores to interface with automatic test equipment through an optimized number of channels. They are well suited for SoC devices comprising both nonisolated cores, i.e., blocks that occasionally need to be tested simultaneously, and completely wrapped modules. Experimental results obtained for large industrial SoC designs illustrate feasibility of the proposed test application schemes and are reported herein.

Thermal-Safe Dynamic Test Scheduling Method Using On-Chip Temperature Sensors for 3D MPSoCs

System test and online test techniques are aggressively being used in today’s SoCs for improved test quality and reliability (e.g., aging/soft-error robustness). With gaining popularity of vertical integration such as 2.5D and 3D, in the semiconductor industry, ensuring thermal safety of SoCs during these test modes poses a challenge. In this paper, we propose a dynamic test scheduling mechanism for system tests and/or online test that uses dynamic feedback from on-chip thermal sensors to control temperature during shift (or scan) and capture, thereby ensuring thermal-safe conditions while applying the test patterns. The proposed technique is a closed loop test application scheme that eliminates the need for separate thermal simulation of test patterns at design stage. The technique also enables granular field-level configuration of thermal limits, so that different units across multiple cores are subjected to customized thermal profiles. Results from implementation of the proposed schemes on a 4-layer, 16-core, 12.8 million gates, OpenSparc S1 processor subsystem are presented.

Transparent-Segmented-Scan without the Routing Overhead of Segmented-Scan

We introduce a combination of segmented-scan and transparent-scan referred to as transparent-segmented-scan. Segmented-scan is a design-for-testability approach for reducing the power dissipation of scan-based tests. Transparent-scan is a test application scheme that was proposed as a way to obtain highly compacted test sequences. The combination allows the generation of compact test sequences with reduced power dissipation. Moreover, since transparent-scan views scan shift and functional capture cycles uniformly, both scan shift and functional capture power are reduced together. We explore a particular implementation of transparent-segmented-scan that does not require the scan chain input and output to be routed to all the segments of a scan chain, as in segmented-scan. This avoids the routing overhead of segmented-scan. It is made possible by the properties of transparent-scan that also contribute to test compaction.

Reducing the switching activity of test sequences under transparent-scan

Transparent-scan is a test application scheme for scan circuits. It provides unique opportunities for test compaction that do not exist with the standard test application scheme. We show that it also provides unique opportunities for reducing the power dissipation of a scan-based test set. After translating a standard scan-based test set into a transparent-scan sequence, we apply two operations for reducing the power dissipation of the sequence. The first operation attempts to remove a test vector that causes high power dissipation. The second operation attempts to replace a scan clock cycle with a functional clock cycle, or a functional clock cycle with a scan clock cycle, in order to reduce the power dissipation. Both operations are implemented such that they reduce the power dissipation without reducing the fault coverage. We also consider a third operation that attempts to complement arbitrary values in the transparent-scan sequence in order to further reduce the power dissipation.

Cost-Effective Power-Aware Core Testing in NoCs Based on a New Unicast-Based Multicast Scheme

Reuse of network-on-chip (NoC) for test data and test response delivery is attractive. However, previous techniques do not effectively use the bandwidths of the network by delivering test packets to all cores separately, which can make very much test cost and test data volume. The NoC core testing problem is formulated as a unicast-based multicast problem in order to reduce test data delivery time in the NoC. Test response data are forwarded back to the automated test equipment (ATE) via the communication channels using the reverse paths of test data delivery, which are compacted on the way from each processor to the ATE. A new power-aware test scheduling scheme is proposed, which is extended to cases for multiple port ATEs. Test data is further compressed before delivering and a low-power test application scheme is used for the cores because power produced by cores is the bottleneck of NoC test. Experimental results are presented to show the effectiveness of the proposed method in reducing the NoC test cost and test data volume by comparing to the previous methods.

A Novel Test Application Scheme for High Transition Fault Coverage and Low Test Cost

This paper presents a new method for improving transition fault coverage in hybrid scan testing. It is based on a novel test application scheme, in order to break the functional dependence of broadside testing. The new technique analyzes the automatic test pattern generation conflicts in broadside test generation and skewed-load test generation, and tries to control the flip-flops with the most influence on fault coverage. The conflict-driven selection method selects some flip-flops that work in the enhanced scan mode or skewed-load scan mode. And the conflict-driven reordering method distributes the selected flip-flops into different chains. In the multiple scan chain architecture, to avoid too many scan-in pins, some chains are driven by the same scan-in pin to construct a tree-based architecture. Based on the architecture, the new test application scheme allows some flip-flops to work in enhanced scan or skewed-load mode, while most of others to work in the traditional broadside scan mode. With the efficient conflict-driven selection and reordering schemes, fault coverage is improved greatly, which can also reduce test application time and test data volume. Experimental results show that fault coverage based on the proposed method is comparable that of enhanced scan.

Improved$n$-Detection Test Sequences Under Transparent Scan

The quality of test sequences for scan circuits under a test-application scheme called transparent scan as n-detection test sequences is studied. A transparent-scan sequence T is obtained from a compact single-detection combinational test set C. It is shown that for the same number of clock cycles required to apply C, the transparent-scan sequence T detects faults more times than C. It is also noted that a transparent-scan sequence based on a combinational test set contains unspecified values. The effects of specifying the unspecified values of the transparent-scan sequence on the quality of the sequence are studied by considering a random specification of these values. A procedure for modifying the scan-select subsequence of a (fully specified) transparent-scan sequence so as to improve its quality as an n-detection test sequence is also described. Finally, the extension of a transparent-scan test sequence into an n-detection test sequence that detects every target fault at least n times is considered. The results show a slower increase in test-application time with n than when combinational test sets are considered

Pseudofunctional testing

Recent research results have shown that the traditional structural testing for delay and signal integrity faults may result in overtesting due to the nontrivial number of such faults that are untestable in the functional mode although testable in the test mode. This paper presents a pseudofunctional-test methodology that attempts to minimize the overtesting problem of the scan-based circuits in automatic test pattern generation (ATPG) and built-in self-test (BIST) test generation approaches. The first pattern of a two-pattern test is still delivered by scan in the test mode but the pattern is generated in such a way that it does not violate the functional constraints extracted from the functional logic. The second pattern is then generated in a functional mode using the functional justification (also called broadside) test application scheme. The authors use a sequential boolean satisfiability solver to extract a set of functional constraints that consists of illegal states and internal signal correlation. The functional constraints are imposed upon an ATPG tool to generate pseudofunctional tests and/or implemented as a monitor in the BIST environment to allow only functional-like patterns generated from the random test pattern generator as tests. The experimental results for delay faults indicate that the percentage of functionally untestable delay faults is nontrivial for many circuits. This finding supports the hypothesis of the overtesting problem in delay testing. In addition, the results indicate the effectiveness of the proposed constraint extraction method and the proposed BIST scheme.

Transparent scan: a new approach to test generation and test compaction for scan circuits that incorporates limited scan operations

We describe a new approach to test generation and test compaction for scan circuits that eliminates the distinction between scan operations and application of primary input vectors. Under this approach, the scan-in, scan-select, and scan-out lines are treated as conventional primary inputs or primary outputs of the circuit. As a result, limited scan operations, where scan chains are shifted a number of times smaller than their lengths, are incorporated naturally into the test sequences generated by this approach. This leads to very aggressive compaction, resulting in test sequences with the lowest known test application times for benchmark circuits. The resulting test sequences can be applied using conventional test application schemes that support limited scan operations.

Theorems for identifying undetectable faults in partial-scan circuits

We provide a definition of undetectable faults in partial-scan circuits under a test application scheme where a test consists of primary input vectors applied at-speed between scan operations. We also provide sufficient conditions for a fault to be undetectable under this test application scheme. We present experimental results on finite-state machine benchmarks to demonstrate the effectiveness of these conditions in identifying undetectable faults.

On the use of random limited-scan to improve at-speed random pattern testing of scan circuits

A method is proposed for improving the fault coverage that can be achieved by random patterns for circuits with scan. Under the test application scheme considered, primary input sequences are applied at-speed between scan operations. The proposed method uses limited scan operations to improve the fault coverage. Under a limited scan operation, the circuit state is shifted by a number of positions which may be smaller than the number of state variables. Limited scan operations are inserted randomly to ensure that the complete test set can be generated by a random pattern generator. Experimental results show that complete fault coverage is achieved by the proposed method, i.e., the proposed method detects all the detectable circuit faults, for all the benchmark circuits considered.

Property-based test generation for scan designs and the effects of the test application scheme and scan selection on the number of detectable faults

Scan circuits are considered under a test application scheme where a test consists of one or more primary input vectors embedded between a scan-in operation and a scan-out operation. The first property-based (simulation-based) test generation procedure under this test application scheme is described. The proposed procedure constructs tests that traverse as many pairs of fault-free/faulty states as possible. Additional techniques are incorporated into this basic procedure to enhance its effectiveness. Also considered for the first time is the set of detectable faults under this test application scheme. It is shown that it is a subset of the set of detectable faults obtained under the test application scheme where scan is applied with every primary input vector. It is also shown that the set of detectable faults depends strongly on the set of scanned flip-flops even when the percentage of scanned flip-flops is very high. This dependence at high levels of scan is significantly weaker when scan is applied with every primary input vector.

On improving test quality of scan-based BIST

In this paper, we explore two techniques, under the existing scan-based built-in self-test (BIST) architectures, for improving the test quality with practically no additional overhead. The proposed techniques are an almost-full-scan BIST strategy and a general scan-based BIST test application scheme. We first demonstrate that under the scan-based BIST architecture, full scan may not result in the highest fault coverage (FC) and unscanning a small number of scan flip-flops may increase the BIST FC. We then present an algorithm for identifying those not-to-be-scanned flip-flops. We further show that the proposed general scan-based BIST test application scheme could also result in higher BIST FC and only requires a minor modification to the BIST controller. Experiments have been conducted using an industrial tool, psb2, on benchmark circuits to illustrate the effectiveness of the proposed techniques and algorithms. The results have demonstrated that both techniques are able to maximize the FC and reduce the test application time without additional test hardware compared to the conventional scan-based BIST architectures.

Design-for-testability for path delay faults in large combinational circuits using test points

We present a method for test-point insertion in large combinational circuits, to increase their path delay fault testability. Using an appropriate test application scheme with multiple clock periods, a test point on a line g divides the set of paths through g for testing purposes into a subset of paths from the primary inputs up to g, and a subset of paths from g to the primary outputs. Each one of these subsets can be tested separately. The number of paths that need to be tested directly is thus reduced. In addition, by breaking an untestable path into two or more testable subpaths, it is possible to obtain a fully testable circuit. Test-point insertion is done to reduce the number of paths, using a time-efficient procedure. Indirectly, it also reduces the number of tests and renders untestable paths testable. When the number of paths is sufficiently small, and if the test generation procedure to be used for the circuit is known, a procedure is given to perform test-point insertion directly targeting the path delay faults that are still untestable. Experimental results are presented to demonstrate the effectiveness of the proposed methods in increasing the testability of large benchmark circuits, and to demonstrate the overheads involved.