FXT is a software tool which implements inductive fault analysis for CMOS circuits. It extracts a comprehensive list of circuit-level faults for any given CMOS circuit and ranks them according to their relative likelihood of occurrence. Five commercial CMOS circuits are analyzed using FXT. Of the extracted faults, approximately 50% can be modeled by single-line stuck-at 0/1 fault model. Faults extracted from two circuits are simulated with the switch-level fault simulator FMOSSIM. The test set provided by the circuits' manufacturer, which detects 100% of the single-line stuck-at 0/1 faults, detected between 73% and 89% of the simulated faults.<<ETX>>

Extraction and Simulation of Realistic CMOS Faults using

This work applies weight based codes to the detection of crosstalk originated errors. This type of fault, whose importance grows with device scaling may originate errors that are undetectable by the commonly used error detecting codes in VLSI ICs. Conversely, such errors can be easily detected by weight based codes that, however, have smaller encoding capabilities. In order to reduce the cost of these codes, a graph theoretic optimization is used. Moreover new applications of these codes are explored regarding the synthesis of self-checking FSMs, and the detection of errors related to the clock distribution network.

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Optimization of error detecting codes for the detection of crosstalk originated errors

Based on real process data of a reference microprocessor, fault models are derived for the manufacturing defects most likely to affect signals of the clock distribution network. Their probability is estimated with Inductive Fault Analysis performed on the actual layout of the reference microprocessor. The effects of the most likely faults have been evaluated by electrical level simulations. We have found that, contrary to common assumptions, only a small percentage of such faults result in catastrophic failures easily detected during manufacturing testing. On the contrary, the majority of such faults lead to local failures not likely to be detected during manufacturing testing, despite their possibly compromising the microprocessor operation and reliability. In particular, we have found that the clock faults can be detected during manufacturing testing in only 12 percent of cases. Even more surprisingly, we have also found that, in 10 percent of cases, the undetected clock faults also invalidate the testing procedure itself.

Implications of clock distribution faults and issues with screening them during manufacturing testing

In this paper we propose a novel buffer scheme that is able to compensate undesired skews between clocks of a synchronous system in a negligible time upon skew occurrence, thus being suitable also for on-line clock-skew correction. Clock signals are aligned one with respect to the other, starting from a reference clock, and moving forward among physically adjacent clock signals, thus creating no problem of reference clock's routing. Our solution is also able to compensate clock duty-cycle variations, which have been shown very likely in case of faults, for instance bridgings, affecting the clock distribution network. Compared to alternate solutions, our proposed scheme enables significant reductions in area overhead and power consumption, and is suitable for on-line compensation. Therefore, it allows clock skew and duty-cycle fault tolerance, thus increasing process yield and system's reliability.

Low cost scheme for on-line clock skew compensation

We propose a clock buffer that is able to compensate clock skews possibly due to process variations, and correct even more severe skews, as those possibly due to faults affecting the clock distribution network or those due to power supply noise. Compensation/correction is performed instantaneously, during system run-time, upon skew occurrence. Compared to alternative solutions which can be used to compensate/correct skews between couples of clocks, that presented here is definitely faster, features lower area overhead and power consumption, and does not require any initialization phase at the beginning of system operation. Additionally, our proposed buffer is also able to compensate/correct clock duty cycle variations due to process parameter variations, as well as faults affecting the clock distribution network. Also in this case, compensation/correction is accomplished within the same clock cycle of duty-cycle variation occurrence.

Fast and low-cost clock deskew buffer

Traditional concurrent-checking techniques may not detect the occurrence of the transient faults and resulting errors likely to affect clock signals in VLSI systems. The authors present a new method and self-checking circuit implementation for concurrently checking the correctness of clock distribution network signals in synchronous systems.

B. Ricco

Papers

Concurrent checking of clock signal correctness