Yield loss caused by excessive power supply noise has become a serious problem in at-speed scan testing. Although X-filling techniques are available to reduce the launch cycle switching activity, their performance may not be satisfactory in the linear-decompressor-based test compression environment. This work is the first to solve this problem by proposing a novel integrated ATPG scheme that efficiently and effectively performs compressible X-filling. Related theoretical principles are established, based on which the problem size is substantially reduced. The proposed scheme is validated by large benchmark circuits as well as an industry design in the embedded deterministic test (EDT) environment.

Reducing Power Supply Noise in Linear-Decompressor-Based Test Data Compression Environment for At-Speed Scan Testing

During an at-speed scan-based test, excessive capture power may cause significant current demand, resulting in the IR-drop problem and unnecessary yield loss. Many methods address this problem by reducing the switching activities of power-risky patterns. These methods may not be efficient when the number of power-risky patterns is large or when some of the patterns require extremely high power. In this paper, we propose discarding all power-risky patterns and starting with power-safe patterns only. Our test generation procedure includes two processes, namely, test pattern refinement and low-power test pattern regeneration. The first process is used to refine the power-safe patterns to detect faults originally detected only by power-risky patterns. If some faults are still undetected after this process, the second process is applied to generate new power-safe patterns to detect these faults. The patterns obtained using the proposed procedure are guaranteed to be power-safe for the given power constraints. To the best of our knowledge, this is the first method that refines only the power-safe patterns to address the capture power problem. Experimental results on ISCAS'89 and ITC'99 benchmark circuits show that an average of 75% of faults originally detected only by power-risky patterns can be detected by refining power-safe patterns and that most of the remaining faults can be detected by the low-power test generation process. Furthermore, the required test data volume can be reduced by 12.76% on average with little or no fault coverage loss.

Capture-Power-Safe Test Pattern Determination for At-Speed Scan-Based Testing

Yield loss caused by excessive power supply noise has become a serious problem in at-speed scan testing. Although X-filling techniques are available to reduce the launch cycle switching activity, their performance may not be satisfactory in the linear-decompressor-based test compression environment. This paper solves this problem by proposing a novel integrated automatic test pattern generation scheme that efficiently and effectively performs compressible low-capture-power X -filling. Related theoretical principles are established, based on which the problem size is substantially reduced. The proposed scheme is validated by benchmark circuits, as well as an industry design in the embedded deterministic test environment.

Power Supply Noise Reduction for At-Speed Scan Testing in Linear-Decompression Environment

We present a programmable method for shift-clock stagger assignment to reduce power supply noise during system-on-chip (SoC) testing. An SoC design is typically composed of several blocks and two neighboring blocks that share the same power rails should not be toggled at the same time during shift. Therefore, the proposed programmable method does not assign the same stagger value to neighboring blocks. The positions of all blocks are first analyzed and the shared boundary length between blocks is then calculated. Based on the position relationships between the blocks, a mathematical model is presented to derive optimal result for small-to-medium sized problems. For larger designs, a heuristic algorithm is proposed and evaluated. We present assignment results as well as power-analysis results and silicon data for industry designs to highlight the effectiveness of the proposed method.

A programmable method for low-power scan shift in SoC integrated circuits

Launch-Switching-Activity (LSA) is a serious problem during at-speed testing of integrated circuits, since localized LSA may lead to severe IR-drop and thus failures. The excessive LSA is conventionally mitigated by reducing the switching activity through special low-power test generation techniques, typically resulting in severe test pattern inflation and high test costs. This work introduces a novel concept of Low-Capture-Power Test Points (LCP-TPs), which are inserted to reduce switching activity in critical High-Capture-Power (HCP) regions. LCP-TPs also help in retaining high test compaction capability. An optimization- SAT based procedure is proposed to compute a small set of optimal LCP-TP locations for compact at-speed test sets with effective capture power reduction. Experimental results clearly demonstrate the advantages of LCP-TP insertion.

Formal Test Point Insertion for Region-based Low-Capture-Power Compact At-Speed Scan Test

Power management is posing serious challenges for scan-based testing. In this paper, we propose a low power test pattern generation technique which minimizes the peak power consumption associated with the scan and capture operations. Given a set of fully specified test patterns, the proposed technique iteratively replaces the high power consumption patterns with low power ones generated by a PODEM-based low power ATPG. The proposed technique has been validated using ISCAS89 benchmark circuits. Compared to a commercial ATPG using high merge ratio and random-fill options, the proposed technique reduces the peak shift and capture power by 27.3% and 19.6%, respectively, and the average power by 49.9%.

An Efficient Peak Power Reduction Technique for Scan Testing

This paper presents a low power test pattern generator, LPTest, that minimizes the peak power consumption during the shift and capture cycles for scan-based stuck-at and transition fault testing. LPTest incorporates both power-aware ATPG and low-power X-filling techniques to achieve higher power reduction. Its enabling technique is a power estimation method which assesses the lower-bounds of the shift-in, shift-out, and capture powers of a partially specified test pattern. The lower-bound estimation method is utilized in LPTest's ATPG engine, dynamic compaction, and X-filling. LPTest has been validated using ISCAS89 benchmark circuits. When considering all cycles, LPTest achieves better than 22% peak WSA (weighted switching activity) reduction for stuck-at and transition faults compared to a commercial ATPG with high merge ratio and random-fill options. Meanwhile, the average power reduction is better than 43%. When only capture power is of concern, LPTest attains more than 46% WSA reduction for stuck-at and transitions.

Kai-Shun Hu

Papers

An Efficient Peak Power Reduction Technique for Scan Testing

LPTest: a Flexible Low-Power Test Pattern Generator