A High Performance Scan Flip-Flop Design for Serial and Mixed Mode Scan Test

Over the years, serial scan design has became the defacto Design for Testability (DFT) technique. The ease of testing and high test coverage has made it to gain wide spread industrial acceptance. However, there are associated penalties with serial scan. These penalties include performance degradation, test data volume, test application time, and test power dissipation. The performance overhead of scan design is due to the scan multiplexers added to the inputs of every flip-flop. In today's very high speed designs with minimum possible combinational depth, the performance degradation caused by scan multiplexer has became magnified. Hence to maintain the circuit performance the timing overhead of scan design must be addressed. In this paper we propose a new scan flip-flop design that eliminates the performance overhead of serial scan. The proposed design removes the scan multiplexer off the functional path. The proposed design can help in improving the functional frequency of performance critical designs. Furthermore, the proposed design can be used as a common scan flip-flop in mixed mode scan test wherein it can be used as a serial scan cell as well as random access scan (RAS) cell

A Cost Effective Technique for Diagnosis of Scan Chain Faults

Scan based diagnosis plays a critical role in failure mode analysis for yield improvement. However, as the logic circuitry associated with scan chains constitute a significant fraction of a chip's total area the scan chain itself can be subject to defects. In some cases, it has been observed that scan chain failures may account up to 50% of total chip failures. Hence, scan chain testing and diagnosis have become very crucial in recent years. This paper proposes a hardware-assisted low complexity and area efficient scan chain diagnosis technique. The proposed technique is simple to implement and provides maximum diagnostic resolution for stuck-at faults. The proposed technique can be further extended to diagnose scan chain's timing faults

S2 - Evaluating Security of New Locking SIB-based Architectures

The IEEE Std 1687 (IJTAG) provides enhanced access to the on-chip test instruments, which are included on the chip for test, post-silicon debug, in field maintenance, and diagnosis purposes. Although the on-chip instruments access provides data and features explicitly for test and debug, these features are misused by the malicious user to access sensitive data such as encryption keys, Chip-IDs, etc. Hence, it is desired to limit the access to sensitive on-chip instruments via IJTAG network. One of the various schemes proposed to mitigate the vulnerability of the IJTAG network is to use a secure access protocol, which is based on LSIB, Chip-ID, and licensed access software. In this paper, the detailed security analysis is performed on IJTAG, it is shown that the secure access protocol technique is vulnerable to differential analysis attack. It can be used to break the secure communication between the board and the licensed access software and thus, the sensitive on-chip test instruments can be accessed illegitimately. It is shown that our proposed algorithm can recover the template used for secure communication within a fraction of a second

A New Scan Flip Flop Design to Eliminate Performance Penalty of Scan

The demand for high performance system-on-chips (SoC) in communication and computing has been growing continuously. To meet the performance goals, very aggressive circuit design techniques such as the use of smallest possible logic depth are being practiced. Replacement of normal flip-flops with scan flip-flops adds an additional multiplexer delay to critical path. Furthermore as the combinational depth decreases, the performance degradation caused by scan multiplexer delay become more critical. Elimination of the scan multiplexer delay off the functional path has become crucial in maintaining the circuit performance. In this work we propose a new transistor level scan cell design to eliminate the scan multiplexer off the functional path. The proposed scan cell uses separate master latch for functional and test mode where as the slave latch is same in both the modes. Our proposed scan flip-flop fully comply with the conventional test flow. Post layout experimental results justify the effectiveness of the proposed scan cell design in eliminating the performance penalty of scan, and thus in improving the timing performance of integrated circuits

Le fonds grec de la Bibliothèque nationale.

Omont Henri. Le fonds grec de la Bibliothèque nationale.. In: Bibliothèque de l'école des chartes. 1883, tome 44. pp. 569-572