Homomorphic Encryption (HE) enables computations to be performed directly on encrypted data, providing strong cryptographic security guarantees and preserving data confidentiality in untrusted environments such as cloud computing, high-performance computing, and machine learning platforms. Among existing HE schemes, Cheon-Kim-Kim-Song (CKKS) enables efficient approximate arithmetic over encrypted real-valued data, making it particularly well suited for numerical workloads. However, its practical deployment remains constrained by the substantial computational cost of its core ciphertext operations. In this work, we present a software-based acceleration of CKKS arithmetic kernels on ARM Neoverse processors through Single Instruction, Multiple Data (SIMD) vectorization using the Scalable Vector Extension (SVE). Our approach targets the widely adopted Microsoft SEAL library and introduces SVE-optimized implementations of the key polynomial-arithmetic primitives underlying CKKS ciphertext addition, multiplication, and rotation. By leveraging data-level parallelism, vector-length-agnostic programming, and microarchitectural features of the target processor, the proposed optimizations enhance execution efficiency while preserving functional correctness and compatibility with the existing library interface. Experimental evaluation on an ARM Neoverse V2 platform (NVIDIA Grace processor) demonstrates performance improvements of 8-14% for ciphertext multiplication and rotation, and approximately 30% for addition, across multiple CKKS parameter configurations. These results highlight the potential for more efficient processor-only execution of homomorphic encryption workloads through architecture-aware optimization.

The CAN protocol, widely used in vehicles, lacks authentication and encryption, making it prone to spoofing, injection, and denial-of-service attacks. This work proposes a detection method based on physical layer signal analysis and unsupervised learning. A custom testbed of eight Arduino nodes with MCP2515 transceivers emulates nominal and attack traffic. Differential voltage signals$(\Delta V=\mathbf{CAN}_{-}\mathbf{H}-\mathbf{CAN}_{-}\mathbf{L})$. are locally captured, segmented, and used to train a lightweight autoencoder. Implemented in TensorFlow, the model achieves 98% accuracy and 93% recall on unauthorized data, and 85% accuracy and 87% recall on spoofed traffic, with 24 ms inference time. The results obtained show that physical layer signals enable efficient and embedded-friendly CAN intrusion detection.

Physically Unclonable Functions (PUFs) have become a promising low-cost solution for authentication and key generation in cryptosystems. However, it has been shown in the literature that the reliability of PUFs is undermined by aging mechanisms, such as Bias Temperature Instability (BTI), which may compromise their correct operation. In this paper, we present a novel ring oscillator (RO) based PUF design that is robust against BTI degradation, hereinafter referred to as Low-sensitive-BTI RO - LBTIRO. We compare our proposed LBTIRO to the standard RO-based PUF and to an alternative NBTI-robust RO-PUF recently presented in the literature, for 90 nm and 32 nm CMOS technology nodes. We show that, for considered technology nodes, our proposed LBTIRO features a higher robustness against BTI. Particularly, our LBTIRO enables a reduction of the impact of BTI on the oscillation frequency over circuit lifetime, which reaches 85.3% and 72.1% against the standard RO and the recent alternate solution, respectively, for the 90 nm technology. Moreover, we show that our proposed LBTIRO features a reduction in terms of power consumption if compared to the alternative NBTIrobust RO-PUF.

Integrated circuits (ICs) may be exposed to counterfeiting due to the involvement of untrusted parties in the semiconductor supply chain; this threatens the security and reliability of electronic systems. This paper focusses on the most common type of counterfeiting namely, recycled and remarked ICs. The goal is to develop a technique to differentiate between new and recycled ICs that have been used for a short period of time. Detecting recycled ICs using aging sensors have been researched using sub-threshold leakage current and frequency degradation utilizing ring oscillators (ROs). The resolution of these sensors requires further development to accurately detect short usage time. This paper proposes a differential aging sensor to detect recycled ICs using ring oscillators with sub-threshold leakage current to detect aging effects using bias temperature instability (BTI) and hot carrier injection (HCI) on a 22-nm CMOS technology, provided by GlobalFoundries. Simulation results confirm that we are able to detect recycled ICs with high confidence using proposed technique. It is shown that the discharge time increases by 14.72% only after 15 days and by 60.49% after 3 years' usage, and outperforms techniques that use frequency degradation only, whilst considering process and temperature variation.

Electronic system components can fall prey to counterfeiting via untrustworthy parties in the semiconductor supply chain, which has established a worldwide span to reduce costs, time to market, and increase productivity. Recently, integrated circuits (ICs) counterfeiting has threatened systems security and reliability that utilize ICs in all domains. This article focuses on the most counterfeited area—recycled and remarked ICs—and aims to develop a technique to distinguish between new and used digital ICs based on an aging sensor mechanism. Aging sensors have been studied based on path-delay fingerprinting and ring oscillators (ROs) frequency degradation, but their resolution requires further development to accurately detect short usage. This study proposes a novel differential aging sensor to measure the discharge time ($\tau {{{dv}}}$) increase that depends on the subthreshold leakage current due to aging with two on-chip designs. Simulations were conducted using the GlobalFoundries (GF) 22 nm for aging with bias temperature instability and hot carrier injection (HCI) combined. The results show that the$\tau {{{dv}}}$increase is 14.72% after 15 days of usage and increases to 60.49% after three years. This further increases at higher temperatures; the highest simulated temperature ($125~^{\circ }\text{C}$)$\tau {{{dv}}}$increases by 55.93% after 15 days and 310.17% after three years. The proposed method also outperformed the traditional frequency degradation-based aging estimation method, which at nominal temperature is found to be 5.00% after 15 days and 23.68% after three years. Therefore, discharge time is a sensitive indicator for aging, surpasses frequency in detecting previous usage and is robust against process, voltage, and temperature variations (PVTs).

Aging is known to impact electronic systems affecting performance and reliability. However, it has been shown that it also brings benefits for power saving and area optimization. This paper presents highlights of those benefits and further shows how aging effects can be leveraged by novel methods to contribute towards improving hardware oriented security and reliability of electronic circuits. We have demonstrated static power reduction in complex circuits from IWLS05 benchmark suite, reaching a noticeable 7S% of reduction in ten years of operation. In hardware oriented security, a novel aging sensor has been proposed for detection of recycled ICs, measuring discharge time Tdv of the virtual power $(VV_{dd)}$ network in power-gated designs. This sensor utilizes discharge time of VVddnetwork through leakage current that is much more sensitive to aging than path delay, exhibiting up to 15.7X increment in 10 years. Furthermore, we show how frequency degradation caused by aging is used for online prediction of remaining useful lifetime (RUL) of electronic circuits. Results show an average RUL prediction deviation of less than 0.1 years. This methodology provides node calculations rather than a mean time to failure (MTTF) of the population. The set of techniques that are presented in this paper takes advantage of aging effects, having a positive impact in various aspects of microelectronic systems.

Embedded DRAMs (eDRAMs) are a promising solution to replace SRAMs for on-chip memories in low-power applications. Gain cells-based eDRAMs, because of their compatibility with standard CMOS process, offer a viable solution to high density storage required by modern SoCs. However, they are usually characterized by a short retention time, which increases their power consumption due to the need of frequent refresh. In this paper, we first analyze the beneficial effects of BTI aging for leakage reduction in eDRAMs and consequent retention time increase. By means of SPICE simulations, we show that, after only a month of operation, retention time increases between 7.2% and 57.9%, depending on cell structure. Retention time increase may exceeds 150% in less than 5 years of operation. Finally, we show how to capitalize on this beneficial effect by adopting an adaptive refresh rate, leading to a significant refresh power reduction over time that, for the considered eDRAM cells, ranges between 10% and 51% in 10 years of operation.

Power-noise viruses can be used as denial-of-service attacks by causing voltage emergencies in multi-core microprocessors that may lead to data corruptions and system crashes. In this paper, we present a run-time system for detecting and mitigating power-noise viruses. We present voltage noise data from a power-noise virus and benchmarks collected from an Arm multi-core processor, and we observe that the frequency of voltage emergencies is dramatically increasing during the execution of power-noise attacks. Based on this observation, we propose a regression model that allows for a run-time estimation of the severity of voltage emergencies by monitoring the frequency of voltage emergencies and the operating frequency of the microprocessor. For mitigating the problem, during the execution of critical tasks that require protection, we propose a system which periodically evaluates the severity of voltage emergencies and adapts its operating frequency in order to honour a predefined severity constraint. We demonstrate the efficacy of the proposed run-time system.

In this paper, we propose a novel technique to detect recycled ICs via an on-chip, coarse-grained aging sensor, which can be applied to low-power circuits featuring power gating. The sensor detects the increase in the power-rail discharge time of power-gated circuits, when the circuit enters the sleep condition. Through HSPICE simulations, we prove that power network discharge time (τdV) is extremely sensitive to the age of the circuit. Indeed, after only 1 month of operation, τdVincreases by more than 3X and, after 1 year, its increase exceeds 7X. Our technique enables the detection of recycled ICs with a very high confidence and is a considerably more sensitive indicator of an aged device that alternative solutions relying on fine-grained performance degradation sensors.

IoT applications with low-budget connected nodes are emerging for a variety of domains, such as smart cities, geomonitoring, parking sensors, surveillance etc. These low-cost nodes contain System-on-Chips (SoCs) with networking capabil- ities. In this paper, we propose to exploit this feature for their dependability management. In particular, we propose collective- awareness, which is a run-time system that emerges when cloud resources are provided to the SoCs for IoT applications for storing information related to their in-the-field status, such as preferable operating modes and performance degradation. Periodically, a dynamic dependability model is constructed by the collected data and SoCs software is updated to meet user-defined lifetime, reliability and performance requirements. To evaluate the operations of the proposed system, we emulate the in-the- field performance degradation of a fleet of a 10K IoT nodes using Monte Carlo on temperature and workload conditions using the largest IWLS’05 benchmarks. During the first two years of system operation, the dynamically constructed model performs lifetime estimation with up to 57% higher accuracy, compared to a static model that considers data only from the design phase of the circuits, while after three years the dynamic model is always accurate for all the devices.

In this paper, we show how beneficial effects of aging on static power consumption can be exploited to design reliable drowsy cache memories adopting dynamic voltage scaling (DVS) to reduce static power. First, we develop an analytical model allowing designers to evaluate the long-term threshold voltage degradation induced by bias temperature instability (BTI) in a drowsy cache memory. Through HSPICE simulations, we demonstrate that, as drowsy memories age, static power reduction techniques based on DVS become more effective because of reduction in subthreshold current due to BTI aging. We develop a simulation framework to evaluate tradeoffs between static power and reliability, and a methodology to properly select the “drowsy” data retention voltage. We then propose different architectures of a drowsy cache memory allowing designers to meet different power and reliability constraints. The performed HSPICE simulations show a soft error rate and static noise margin improvement up to 20.8% and 22.7%, respectively, compared to standard aging unaware drowsy technique. This is achieved with a limited static power increase during the very early lifetime, and with static energy saving of up to 37% in 10 years of operation, at no or very limited hardware overhead.

Manufacturing defects that do not affect the functional operation of low power integrated circuits (ICs) can nevertheless impact their power saving capability. We show that stuck-ON faults on the power switches and resistive bridges between the power networks can impair the power saving capability of power-gating designs. For quantifying the impact of such faults on the power savings of power-gating designs, we propose a diagnosis technique that targets bridges between the power networks. The proposed technique is based on the static power analysis of a power-gating design in stand-by mode and it utilizes a novel on-chip signature generation unit, which is sensitive to the voltage level between power rails, the measurements of which are processed off-line for the diagnosis of bridges that can adversely affect power savings. We explore, through SPICE simulation of the largest IWLS’05 benchmarks synthesized using a 32 nm CMOS technology, the tradeoffs achieved by the proposed technique between diagnosis accuracy and area cost and we evaluate its robustness against process variation. The proposed technique achieves a diagnosis resolution that is higher than 98.6% and 97.9% for bridges of${R}~{\gtrsim }~{10~{ M}\Omega }$(weak bridges) and bridges of${R~\lesssim~10~{ M}\Omega }$(strong bridges), respectively, and a diagnosis accuracy higher than 94.5% for all the examined defects. The area overhead is small and scalable: it is found to be 1.8% and 0.3% for designs with 27 K and 157 K gate equivalents, respectively.

Electronic devices with power-constrained embedded systems are used for a variety of IoT applications, such as geo-monitoring, parking sensors and surveillance, which may tolerate few errors and may not be constrained by a strict error detection latency requirement. In this poster, we propose a novel low power online error monitoring technique that produces an alarm signal when systematic erroneous behaviour has occurred over a pre-defined time interval. A monitoring architecture monitors the signal probabilities of the logic cones concurrently to its normal operation and compares them on-chip against the signature of error-free behaviour. Results on a set of the EPFL'15 benchmarks show an average error coverage of 82.9%% of errors induced by stuck-at faults, with an average area cost of 1.2% and an error detection latency of [0.01, 3.3] milliseconds.

Low power fault tolerance design techniques trade reliability to reduce the area cost and the power overhead of integrated circuits by protecting only a subset of their workload or their most vulnerable parts. However, in the presence of faults not all workloads are equally susceptible to errors. In this paper, we present a low power fault tolerance design technique that selects and protects the most susceptible workload. We propose to rank the workload susceptibility as the likelihood of any error to bypass the logic masking of the circuit and propagate to its outputs. The susceptible workload is protected by a partial Triple Modular Redundancy (TMR) scheme. We evaluate the proposed technique on timing-independent and timing-dependent errors induced by permanent and transient faults. In comparison with unranked selective fault tolerance approach, we demonstrate a) a similar error coverage with a 39.7% average reduction of the area overhead or b) a 86.9% average error coverage improvement for a similar area overhead. For the same area overhead case, we observe an error coverage improvement of 53.1% and 53.5% against permanent stuck-at and transition faults, respectively, and an average error coverage improvement of 151.8% and 89.0% against timing-dependent and timing-independent transient faults, respectively. Compared to TMR, the proposed technique achieves an area and power overhead reduction of 145.8% to 182.0%.

The generation of significant power droop (PD) during at-speed test performed by Logic Built-In Self Test (LBIST) is a serious concern for modern ICs. In fact, the PD originated during test may delay signal transitions of the circuit under test (CUT): an effect that may be erroneously recognized as delay faults, with consequent erroneous generation of test fails and increase in yield loss. In this paper, we propose a novel scalable approach to reduce the PD during at-speed test of sequential circuits with scan-based LBIST using the launch-on-capture scheme. This is achieved by reducing the activity factor of the CUT, by proper modification of the test vectors generated by the LBIST of sequential ICs. Our scalable solution allows us to reduce PD to a value similar to that occurring during the CUT in field operation, without increasing the number of test vectors required to achieve a target fault coverage (FC). We present a hardware implementation of our approach that requires limited area overhead. Finally, we show that, compared with recent alternative solutions providing a similar PD reduction, our approach enables a significant reduction of the number of test vectors (by more than 50%), thus the test time, to achieve a target FC.

In this paper, we present a novel coarse-grained technique for monitoring online the bias temperature instability (BTI) aging of circuits by exploiting their power gating infrastructure. The proposed technique relies on monitoring the discharge time of the virtual-power-network during standby operations, the value of which depends on the threshold voltage of the CMOS devices in a power-gated design (PGD). It does not require any distributed sensors, because the virtual-power-network is already distributed in a PGD. It consists of a hardware block for measuring the discharge time concurrently with normal standby operations and a processing block for estimating the BTI aging status of the PGD according to collected measurements. Through SPICE simulation, we demonstrate that the BTI aging estimation error of the proposed technique is less than 1% and 6.2% for PGDs with static operating frequency and dynamic voltage and frequency scaling, respectively. Its area cost is also found negligible. The power gating minimum idle time (MIT) cost induced by the energy consumed for monitoring the discharge time is evaluated on two scalar machine models using either x86 or ARM instruction sets. It is found less than 1.3× and 1.45× the original power gating MIT, respectively. We validate the proposed technique through accelerated aging experiments conducted with five actual chips that contain an ARM cortex M0 processor, manufactured with a 65 nm CMOS technology.

This paper provides a comprehensive evaluation of the effects of Bias Temperature Instability (BTI) aging on the delay of level shifters. The latter are indispensable blocks in energy efficient systems with multiple supply voltages. Our results show that conventional level-up shifters exhibit significantly more aging-induced delay degradation compared to standard logic cells. Our experiments performed in a predictive 32nm technology indicate those designs can suffer from more than 200% increase in their delay after 5 years due to BTI aging compared to an average of 20% delay rise in the case of standard CMOS logic. Our investigations show that the reason behind this phenomenon is the differential signaling structure present in the majority of conventional level up shifters, combined with the use of low supply voltages.

During at-speed test of high performance sequential ICs using scan-based Logic BIST, the IC activity factor (AF) induced by the applied test vectors is significantly higher than that experienced during its in field operation. Consequently, power droop (PD) may take place during both shift and capture phases, which will slow down the circuit under test (CUT) signal transitions. At capture, this phenomenon is likely to be erroneously recognized as due to delay faults. As a result, a false test fail may be generated, with consequent increase in yield loss. In this paper, we propose two approaches to reduce the PD generated at capture during at-speed test of sequential circuits with scan-based Logic BIST using the Launch-On-Shift scheme. Both approaches increase the correlation between adjacent bits of the scan chains with respect to conventional scan-based LBIST. This way, the AF of the scan chains at capture is reduced. Consequently, the AF of the CUT at capture, thus the PD at capture, is also reduced compared to conventional scan-based LBIST. The former approach, hereinafter referred to as Low-Cost Approach (LCA), enables a 50 percent reduction in the worst case magnitude of PD during conventional logic BIST. It requires a small cost in terms of area overhead (of approximately 1.5 percent on average), and it does not increase the number of test vectors over the conventional scan-based LBIST to achieve the same Fault Coverage (FC). Moreover, compared to three recent alternative solutions, LCA features a comparable AF in the scan chains at capture, while requiring lower test time and area overhead. The second approach, hereinafter referred to as High-Reduction Approach (HRA), enables scalable PD reductions at capture of up to 87 percent, with limited additional costs in terms of area overhead and number of required test vectors for a given target FC, over our LCA approach. Particularly, compared to two of the three recent alternative solutions mentioned above, HRA enables a significantly lower AF in the scan chains during the application of test vectors, while requiring either a comparable area overhead or a significantly lower test time. Compared to the remaining alternative solutions mentioned above, HRA enables a similar AF in the scan chains at capture (approximately 90 percent lower than conventional scan-based LBIST), while requiring a significantly lower test time (approximately 4.87 times on average lower number of test vectors) and comparable area overhead (of approximately 1.9 percent on average).

In this paper, we show that negative bias temperature instability (NBTI) aging of sleep transistors (STs), together with its detrimental effect for circuit performance and lifetime (LT), presents considerable benefits for power-gated circuits. Indeed, it reduces static power due to leakage current, and increases ST switch efficiency, making power gating more efficient and effective over time. The magnitude of these aging benefits depends on operating and environmental conditions. By means of HSPICE simulations, considering a 32-nm CMOS technology, we demonstrate that static power may reduce by more than 80% in 10 years of operation. Static power decrease over time due to NBTI aging is also proven experimentally, using a test chip manufactured with a 65-nm technology. We propose an ST design strategy for reliable power gating, in order to harvest the benefits offered by NBTI aging. It relies on the design of STs with a proper lower$V_{\textrm {th}}$compared with the standard STs. This can be achieved by either redesigning the STs with the identified$V_{\textrm {th}}$value or applying a proper forward body bias to the available power switching fabrics. Through the HSPICE simulations, we show LT extension up to$21.4\times $and average static power reduction up to 16.3% compared with the standard ST design approach, without additional area overhead. Finally, we show LT extension and several performance-cost tradeoffs when a target maximum LT is considered.

In this paper we show that power gating techniques become more effective during their lifetime, since the aging of sleep transistors (STs) due to negative bias temperature instability (NBTI) drastically reduces leakage power. Based on this property, we propose an NBTI and leakage aware ST design method for reliable and energy efficient power gating. Through SPICE simulations, we show lifetime extension up to 19.9x and average leakage power reduction up to 14.4% compared to standard STs design approach without additional area overhead. Finally, when a maximum 10-year lifetime target is considered, we show that the proposed method allows multiple beneficial options compared to a standard STs design method: either to improve circuit operating frequency up to 9.53% or to reduce ST area overhead up to 18.4%.

This paper examines diagnosis of power switches when the power-distribution-network (PDN) is considered as a high resolution distributed electrical model. The analysis shows that for a diagnosis method to perform high diagnosis accuracy and resolution, the distributed nature of PDN should not be simplified by a lumped model. For this reason, a PDN-aware diagnosis method for power switches fault grading is proposed. The proposed method utilizes a novel signature generation design-for-testability (DFT) unit, the signatures of which are processed by a novel diagnosis algorithm that grades the magnitude of faults. Through simulations of physical layout SPICE models, we explore the trade-offs of the proposed method between diagnosis accuracy and diagnosis resolution against area overhead and we show that 100% diagnosis accuracy and up to 98% diagnosis resolution can be achieved with negligible cost.

We propose a novel dynamic voltage scaling (DVS) approach for reliable and energy efficient cache memories. First, we demonstrate that, as memories age, leakage power reduction techniques become more effective due to sub-threshold current reduction with aging. Then, we provide an analytical model and a design exploration framework to evaluate trade-offs between leakage power and reliability, and propose a BTI and leakage aware selection of the “drowsy” state retention voltage for DVS of cache memories. We propose three DVS policies, allowing us to achieve different power/reliability trade-offs. Through SPICE simulations, we show that a critical charge and a static noise margin increase up to 150% and 34.7%, respectively, is achieved compared to standard aging unaware drowsy technique, with a limited leakage power increase during the very early lifetime, and with leakage energy saving up to 37% in 10 years of operation. These improvements are attained at zero or negligible area cost.

This paper shows that existing delay-based testing techniques for power gating exhibit both fault coverage and yield loss due to deviations at the charging delay introduced by the distributed nature of the power-distribution-networks (PDNs). To restore this test quality (TQ) loss, which could reach up to 67.7% of false passes and 25% of false fails due to stuck-open faults, we propose a design-for-testability logic that accounts for a distributed PDN. The proposed logic is optimized by an algorithm that also handles uncertainty due to process variations and offers tradeoff flexibility between test application time and area cost. A calibration process is proposed to bridge model-to-hardware discrepancies and increase TQ when considering systematic variations. Through SPICE simulations, we show complete recovery of the TQ lost due to PDNs. The proposed method is robust, sustaining 80.3%–98.6% of the achieved TQ under high random and systematic process variations. To the best of our knowledge, this paper presents the first analysis of the PDN impact on TQ and offers a unified test solution for both ring and grid power gating styles.

In this paper, we present a low-cost, on-chip clock jitter digital measurement scheme for high performance microprocessors. It enablesin situjitter measurement during the test or debug phase. It provides very high measurement resolution and accuracy, despite the possible presence of power supply noise (representing a major source of clock jitter), at low area and power costs. The achieved resolution is scalable with technology node and can in principle be increased as much as desired, at low additional costs in terms of area overhead and power consumption. We show that, for the case of high performance microprocessors employing ring oscillators (ROs) to measure process parameter variations (PPVs), our jitter measurement scheme can be implemented by reusing part of such ROs, thus allowing to measure clock jitter with a very limited cost increase compared with PPV measurement only, and with no impact on parameter variation measurement resolution.

In this paper, we address the problem of modeling the thermal behavior of photovoltaic (PV) cells undergoing a hotspot condition. In case of shading, PV cells may experience a dramatic temperature increase, with consequent reduction of the provided power. Our model has been validated against experimental data, and has highlighted a counterintuitive PV cell behavior, that should be considered to improve the energy efficiency of PV arrays. Then, we propose a hotspot detection scheme, enabling to identify the PV module that is under hotspot condition. Such a scheme can be used to avoid the permanent damage of the cells under hotspot, thus their drawback on the power efficiency of the entire PV system.

In this paper, we address the issue of analyzing the effects of aging mechanisms on ICs' soft error (SE) susceptibility. In particular, we consider bias temperature instability (BTI), namely negative BTI in pMOS transistors and positive BTI in nMOS transistors that are recognized as the most critical aging mechanisms reducing the reliability of ICs. We show that BTI reduces significantly the critical charge of nodes of combinational circuits during their in-field operation, thus increasing the SE susceptibility of the whole IC. We then propose a time dependent model for SE susceptibility evaluation, enabling the use of adaptive SE hardening approaches, based on the ICs lifetime.

Significant peak power (PP), thus power droop (PD), during test is a serious concern for modern, complex ICs. In fact, the PD originated during the application of test vectors may produce a delay effect on the circuit under test signal transitions. This event may be erroneously recognized as presence of a delay fault, with consequent generation of an erroneous test fail, thus increasing yield loss. Several solutions have been proposed in the literature to reduce the PD during test of combinational ICs, while fewer approaches exist for sequential ICs. In this paper, we propose a novel approach to reduce peak power/power droop during test of sequential circuits with scan-based Logic GIST. In particular, our approach reduces the switching activity of the scan chains between following capture cycles. This is achieved by an original generation and arrangement of test vectors. The proposed approach presents a very low impact on fault coverage and test time, while requiring a very low cost in terms of area overhead.

Performance degradation of integrated circuits due to aging effects, such as Negative Bias Temperature Instability (NBTI), is becoming a great concern for current and future CMOS technology. In this paper, we propose two monitoring and masking approaches that detect late transitions due to NBTI degradation in the combinational part of critical data paths and guarantee the correctness of the provided output data by adapting the clock frequency. Compared to recently proposed alternative solutions, one of our approaches (denoted as Low Area and Power (LAP) approach) requires lower area overhead and lower, or comparable, power consumption, while exhibiting the same impact on system performance, while the other proposed approach (denoted as High Performance (HP) approach) allows us to reduce the impact on system performance, at the cost of some increase in area and power consumption.

We analyze the effects of faults on an energy-harvesting circuit (EHC) providing power to a wireless biomedical multisensor node. We show that such faults may prevent the EHC from producing the power supply voltage level required by the multisensor node. Then, we propose a low-cost (in terms of power consumption and area overhead) additional circuit monitoring the voltage level produced by the EHC continuously, and concurrently with the normal operation of the device. Such a monitor gives an error indication if the generated voltage falls below the minimum value required by the sensor node to operate correctly, thus allowing the activation of proper recovery actions to guarantee system fault tolerance. The proposed monitor is self-checking with regard to the internal faults that can occur during its in-field operation, thus providing an error signal when affected by faults itself.

In this paper we address the issue of improving ECC correction ability beyond that provided by the standard SEC/DED Hsiao code. We analyze the impact of the standard SEC/DED Hsiao ECC and for several double error correcting (DEC) codes on area overhead and cache memory access time for different codeword sizes and code-segment sizes, as well as their correction ability as a function of codeword/code-segment sizes. We show the different trade-offs that can be achieved in terms of impact on area overhead, performance and correction ability, thus giving insight to designers for the selection of the optimal ECC and codeword organization/code-segment size for a given application.

First, a new high-performance robust latch (referred to as HiPeR latch) is presented that is insensitive to transient faults affecting its internal and output nodes by design, independently of the size of its transistors. Then, a modified version of the HiPeR latch (referred as HiPeR-CG) is proposed that is suitable to be used together with clock gating. Both proposed latches are faster than the latches most recently presented in the literature, while providing better or comparable robustness to transient faults, at comparable or lower costs in terms of area and power, respectively. Therefore, thanks to the good trade-offs in terms of performance, robustness, and cost, our proposed latches are particularly suitable to be adopted on critical paths.

In this paper, we present an accurate linear model for estimating the minimum amount of collected charge due to an energetic particle striking a combinational circuit node that may give rise to a SET with an amplitude larger than the noise margin of the subsequent gates. This charge value will be referred to as SET critical charge (Q SET ). Our proposed model allows to calculate the Q SET of a node as a function of the size of the transistors of the gate driving the node and the fan-out gate(s), with no need for time costly electrical level simulations. This makes our approach suitable to be integrated into a design automation tool for circuit radiation hardening. The proposed model features 96% average accuracy compared to electrical level simulations performed by HSPICE. Additionally, it highlights that Q SET has a much stronger dependence on the strength of the gate driving the node, than on the node total capacitance. This property could be considered by robust design techniques in order to improve their effectiveness.

We propose an on-line testing approach for the control logic of high performance microprocessors. Rather than adding information redundancy (in the form of error detecting codes), we propose to look for the information redundancy (referred to as Function-Inherent Codes) that the microprocessor control logic may inherently have, due to its required functionality. We will show that this allows to achieve on-line testing at significant savings in terms of area and power consumption, and with lower or comparable impact on system performance and design costs, compared to alternate, traditional on-line testing approaches.

We analyze the electrical phenomena that can affect the integrity of the communication among different chips within a System in Package (SiP). We address these issues for a real case, for which electrical parameters are extracted from layout and used to build a netlist employed for electrical characterization. We show that crosstalk, and in particular inductive crosstalk, is the electrical phenomenon mainly affecting signal transmission within the SiP. Then,we evaluate the kinds of errors that can be originated. We show that errors caused by inductive coupling among SiP interconnects can be unidirectional only, thus allowing designers to implement error control coding techniques based on All Unidirectional Error Detecting codes. This allows significant cost reduction over the alternate use of non-unidirectional error detecting codes.

On-chip interconnects in very deep submicrometer technology are becoming more sensitive and prone to errors caused by power supply noise, crosstalk, delay variations and transient faults. Error-correcting codes (ECCs) can be employed in order to provide signal transmission with the necessary data integrity. In this paper, the impact of ECCs to encode the information on a very deep submicrometer bus on bus power consumption is analyzed. To fulfill this purpose, both the bus wires (with mutual capacitances, drivers, repeaters and receivers) and the encoding–decoding circuitry are accounted for. After a detailed analysis of power dissipation in deep submicrometer fault-tolerant busses using Hamming single ECCs, it is shown that no power saving is possible by choosing among different Hamming codes. A novel scheme, called Dual Rail, is then proposed. It is shown that Dual Rail, combined with a proper bus layout, can provide a reduction of energy consumption. In particular, it is shown how the passive elements of the bus (bottom and mutual wire capacitances), active elements of the bus (buffers) and error-correcting circuits contribute to power consumption, and how different tradeoffs can be achieved. The analysis presented in this paper has been performed considering a realistic bus structure, implemented in a standard 0.13- $\mu{\hbox{m}}$ CMOS technology.

In this paper we propose a novel error control scheme to cope with errors affecting the communication links of a NoC. Our scheme can be configured in Correction Mode, Detection Mode, and Mixed Mode, depending on the particular application, thus allowing to meet different Quality of Service (QoS) levels in terms of error control. For each configuration mode, we propose different error control policies and we consider SEC Hamming codes, SEC/DED Hsiao codes, and Symbol Error Correcting codes. We evaluate advantages and drawbacks of each approach, in terms of signal integrity, area overhead and impact on performance.

In today's high performance (multi-GHz) microprocessors' design, on-chip clock calibration features are needed to compensate for electrical parameter variations as a result of manufacturing process variations. The calibration features allow performance boost after manufacturing test and maintain such performance levels during normal operation, thus preserving product quality. This strategy has been proven successful commercially. In this paper, we discuss the impact on performance and product quality of both permanent and transient faults possibly affecting these calibration circuits during manufacturing and normal operation, respectively. In particular, we consider the case of an on-chip clock calibration feature of a commercial high performance microprocessor. We will show that some possible permanent faults may render the on-chip clock calibration schemes useless (in process variations' compensation), while it is impossible for common manufacturing testing to detect this incorrect behavior. This means that a faulty operating microprocessor may pass the testing phase and be put onto the market, with a consequent impact on product quality and increase in Defect Level. Similarly, we will show that some possible transient faults occurring during the microprocessor in-field operation could defeat the purpose of on-chip clock calibration, again resulting in faulty operation of the microprocessor. This has long range implications to microprocessors' design as well, considering that process variations on die, as well as across the process, would worsen with continued scaling. Proper strategies to test these clock calibration features and to guarantee their correct operation in the field cannot be ignored. Possible design approaches to solve this problem will be discussed.

In this paper we analyze the conditions making Transient Faults (TFs) affecting the nodes of conventional latch structures generate output Soft-Errors (SEs). We investigate the susceptibility to TFs of all latch nodes and identify the most critical one(s). We show that, for standard latches using back-to-back inverters for their positive feedback, the internal nodes within their feedback path are the most critical. Such nodes will be hereafter referred to as internal feedback nodes. Based on this analysis, we first propose a low cost hardened latch that, compared to alternative hardened solutions, is able to filter out completely TFs affecting its internal feedback nodes, while presenting a lower susceptibility to TFs on the other internal nodes. This is achieved at the cost of a reduced robustness to TFs affecting the output node. To overcome this possible limitation (especially for systems for high reliability applications), we propose another version of our latch that, at the cost of a small area and power consumption increase compared to our first solution, improves also the robustness of the output node, which can be higher than that of alternative hardened solutions. Additionally, both proposed latches present a comparable or higher robustness of the input node than alternative solutions and provide a lower or comparable power-delay product and area overhead than classical implementations and alternative hardened solutions.

In this paper we present a novel circuit for the online detection of transient and crosstalk faults affecting the interconnects of systems implemented using Field Programmable Gate-Arrays (FPGAs). The proposed detector features self-checking ability with respect to faults possibly affecting itself, thus being suitable for systems with high reliability requirements, like those for space applications. Compared to alternate solutions, the proposed circuit requires a significantly lower area overhead, while implying a comparable, or lower, impact on system performance. We have verified our circuit operation and self-checking ability by means of post-layout simulations.

In this paper, we analyze the impact of error detecting codes, implemented on an on-chip bus, on the on-chip simultaneous switching noise (SSN). First, we analyze in detail how SSN is impacted by different bus transitions, pointing out its dependency on the number and placement of switching wires. Afterwards, we present an analytical model that we have developed in order to estimate the SSN, and that we prove to be very accurate in SSN prediction. Finally, by employing the developed model, we estimate the SSN due to different EDCs implemented on an on-chip bus. In particular, we highlight how their differences in the number of switching wires, bus parallelism and codewords influence the on-chip SSN.

Min delay violations are traditionally not modeled as possible faults as a result of manufacturing defects. Usually, path delay faults are implicitly assumed to be paths' max delay violations. This, in turn, is based on the assumption that min delay violations are designed out. Most previous manufacturing defect/fault analysis works have not considered their effect on clock circuits. More recently, as burn-in becomes ineffective and process variations become more of an issue, latent defects, device degradation or wear out in the field would potentially also cripple the clock distribution network. Consequently, we should start considering also path (min) delay faults when designing on-line testable circuits, similar to what we currently do for path (max) delay faults. The challenges that this poses to the existing on-line testing strategies are discussed. Examples showing the possible incorrect behavior of a self-checking circuit as a result of this kind of faults are given. New on-line testing strategies should consequently be devised to deal with these faults

In this paper we evaluate the probability that a transient fault (TF), multiple or single, affecting a checker of a self-checking circuit, gives rise to an unnecessary error indication (no-harm alarm). A new property (no-harm alarm robustness) has been defined that, in case of a fault affecting a self-checking circuit (SCC), guarantees that we can determine whether the fault is affecting the functional block, or the checker itself, and whether such a fault is a transient or a permanent fault. Finally, we propose a possible solution implementing the defined property. Its behavior has been verified by means of HSpice simulations, and we evaluate its cost in terms of area overhead and introduced delay

In this paper we present a detailed analysis on how the critical charge (Q/sub crit/) of a circuit node, usually employed to evaluate the probability of transient fault (TF) occurrence as a consequence of a particle hit, depends on transistors' sizing. We derive an analytical model allowing us to calculate a node's Q/sub crit/ given the size of the node's driving gate and fan-out gate(s), thus avoiding time costly electrical level simulations. We verified that such a model features an accuracy of the 97% with respect to electrical level simulations performed by HSPICE. Our proposed model shows that Q/sub crit/ depends much more on the strength (conductance) of the gate driving the node, than on the node total capacitance. We also evaluated the impact of increasing the conductance of the driving gate on TFs' propagation, hence on soft error susceptibility (SES). We found that such a conductance increase not only improves the TF robustness of the hardened node, but also that of the whole circuit.

As device geometries shrink, power supply voltage decreases, and chip complexity increases, the noise induced by the increased amount of simultaneously switching devices (especially the strong bus drivers (SSN)), is becoming crucial in determining the signal integrity of a system. In this paper we propose ways of merging transition reducing coding techniques with coding techniques for fault tolerant busses (implementing either error detecting codes and error recovery, or correcting codes). In particular, we focus on merging bus-invert code along with the employed error detection or correction coding technique, and show that the maximum number of simultaneous switching drivers can be drastically reduced, thus reducing the SSN and increasing signal integrity. Furthermore, we show how, by properly merging the bus invert encoder and the check bit generator, the latency introduced by the proposed coding techniques can be minimized and the number of additional wires can be kept minimal.

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.

We propose a compact, high-speed, and highly testable parallel two-rail code checker, particularly suitable to implementing embedded checkers. In fact, it requires only two input codewords to satisfy the totally-self-checking or strongly code-disjoint property with respect to a wide set of realistic internal faults. Our checker can be employed to check the correct operation of a connected functional block using the two-rail code, to implement the output two-rail code checker of "normal" checkers for unordered codes, or to join together the error messages produced by various checkers (possibly using different codes) present within the same self-checking system. The behavior of our checker has been verified by means of electrical level simulations (performed using HSPICE), considering both nominal values and statistical variations of electrical parameters. We also propose a possible modification to our checker internal structure that makes it able to provide an output error indication remaining latched until the application of a proper reset signal. Depending on the considered application and recovery technique to be employed upon the generation of an error indication at the checker output, one proposed solution or the other may be preferable.

Transient faults (TFs) are increasingly affecting micro-electronic devices as their size decreases. During the design phase, the robustness of circuits for high reliability applications with respect to this kind of faults is generally validated through simulations. However, traditional HSPICE like simulators are too slow for the task of simulating the effects of TFs on large circuits. In this paper, we present a novel mathematical model to accurately estimate the possible propagation of transient fault-due glitches through a CMOS combinational circuit, which is suitable to be used into a new simulation tool able to provide good accuracy, while significantly speeding up simulations, with respect to HPSICE. In particular, our model allows approximately 90% accuracy with respect to HSPICE simulations.

On-chip global interconnections in very deep submicron technology (VDSM) ICs are becoming more sensitive and prone to errors caused by power supply noise, crosstalk noise, delay variations and transient faults. Error correcting codes can be employed in order to provide signal transmission with the necessary data integrity. We compared Dual Rail encoding versus Hamming with respect to power consumption of the bus wires themselves (passive capacity model) [Rossi et al., 2002]. In this paper we analyze the contribution of the active elements of both coding schemes. We first present a detailed analysis of the power consumption of an encoded bus, taking into account the bus wires (with mutual capacitances, drivers, repeaters and receivers), as well as the encoding/decoding circuitry. Then we compare the two considered coding technique with respect to the power consumption, and we show how different tradeoffs can be achieved. Our analysis is based on a realistic bus structure, implemented in a 0.13/spl mu/m CMOS technology.

In this paper we present a technique which allows to reduce the crosstalk-induced delay within busses implementing an error detecting/correcting code. This technique is based on the observation that the maximum delay on an encoded bus is usually due to the check bits that are added to provide the desired error detection/ tolerance ability. These bits, in fact, are computed from the bus information bits by an ad hoc encoder, which adds an extra delay to the crosstalk-induced bus delay. We will show that, by proper placement of the lines carrying the information with respect to those carrying the check bits, it is possible to reduce the effective coupling capacitance due to the Miller effect among adjacent lines. This allows a reduction of propagation delay which, depending on the implemented code, can overcome the 20% with respect to the conventional placement of encoded busses.

University of Bologna