An Efficient Algorithm for the Analysis of Cyclic Circuits

Compiling high-level hardware languages can produce circuits containing combinational cycles that can never be sensitized. Such circuits do have well-defined functional behavior, but wreak havoc with most logic synthesis and timing tools, which assume acyclic combinational logic. As such, some sort of cycle-removal step is usually necessary for handling these circuits. We present an algorithm able to quickly and exactly characterize all combinational behavior of a cyclic circuit. It iteratively examines the boundary between gates whose outputs are and are not defined and works backward to find additional input patterns that make the circuit behave combinationally. It produces a minimal set of sets of assignments to inputs that together cover all combinational behavior. This can be used to restructure the circuit into an acyclic equivalent, report errors, or as an optimization aid. Experiments show our algorithm runs several orders of magnitude faster than existing ones on real-life cyclic circuits, making it useful in practice

Testing of leakage current failure in ASIC devices exposed to total ionizing dose environment using design for testability techniques

Due to the advancements in technology, electronic devices have been relied upon to operate under harsh conditions. Radiation is one of the main causes of different failures of the electronics devices. According to the operation environment, the sources of the radiation can be terrestrial or extra-terrestrial. For terrestrial the devices can be used in nuclear reactors or biomedical devices where the radiation is man-made. While for the extra- terrestrial, the devices can be used in satellites, the international space station or spaceships, where the radiation comes from various sources like the Sun. According to the operation environment the effects of radiation differ. These effects falls under two categories, total ionizing dose effect (TID) and single event effects (SEEs). TID effects can be affect the delay and leakage current of CMOS circuits negatively. The affects can therefore hinder the integrated circuits\u27 operation. Before the circuits are used, particularly in critical radiation heavy applications like military and space, testing under radiation must be done to avoid any failures during operation. The standard in testing electronic devices is generating worst case test vectors (WCTVs) and under radiation using these vectors the circuits are tested. However, the generation of these WCTVs have been very challenging so this approach is rarely used for TIDs effects. Design for testability (DFT) have been widely used in the industry for digital circuits testing applications. DFT is usually used with automatic test patterns generation software to generate test vectors against fault models of manufacturer defects for application specific integrated circuit (ASIC.) However, it was never used to generate test vectors for leakage current testing induced in ASICs exposed to TID radiation environment. The purpose of the thesis is to use DFT to identify WCTVs for leakage current failures in sequential circuits for ASIC devices exposed to TID. A novel methodology was devised to identify these test vectors. The methodology is validated and compared to previous non DFT methods. The methodology is proven to overcome the limitation of previous methodologies

Doctor of Philosophy

dissertationThe design of integrated circuit (IC) requires an exhaustive verification and a thorough test mechanism to ensure the functionality and robustness of the circuit. This dissertation employs the theory of relative timing that has the advantage of enabling designers to create designs that have significant power and performance over traditional clocked designs. Research has been carried out to enable the relative timing approach to be supported by commercial electronic design automation (EDA) tools. This allows asynchronous and sequential designs to be designed using commercial cad tools. However, two very significant holes in the flow exist: the lack of support for timing verification and manufacturing test. Relative timing (RT) utilizes circuit delay to enforce and measure event sequencing on circuit design. Asynchronous circuits can optimize power-performance product by adjusting the circuit timing. A thorough analysis on the timing characteristic of each and every timing path is required to ensure the robustness and correctness of RT designs. All timing paths have to conform to the circuit timing constraints. This dissertation addresses back-end design robustness by validating full cyclical path timing verification with static timing analysis and implementing design for testability (DFT). Circuit reliability and correctness are necessary aspects for the technology to become commercially ready. In this study, scan-chain, a commercial DFT implementation, is applied to burst-mode RT designs. In addition, a novel testing approach is developed along with scan-chain to over achieve 90% fault coverage on two fault models: stuck-at fault model and delay fault model. This work evaluates the cost of DFT and its coverage trade-off then determines the best implementation. Designs such as a 64-point fast Fourier transform (FFT) design, an I2C design, and a mixed-signal design are built to demonstrate power, area, performance advantages of the relative timing methodology and are used as a platform for developing the backend robustness. Results are verified by performing post-silicon timing validation and test. This work strengthens overall relative timed circuit flow, reliability, and testability

Identifying worst case test vectors for FPGA exposed to total ionization dose using design for testability techniques

Electronic devices often operate in harsh environments which contain a variation of radiation sources. Radiation may cause different kinds of damage to proper operation of the devices. Their sources can be found in terrestrial environments, or in extra-terrestrial environments like in space, or in man-made radiation sources like nuclear reactors, biomedical devices and high energy particles physics experiments equipment. Depending on the operation environment of the device, the radiation resultant effect manifests in several forms like total ionizing dose effect (TID), or single event effects (SEEs) such as single event upset (SEU), single event gate rupture (SEGR), and single event latch up (SEL). TID effect causes an increase in the delay and the leakage current of CMOS circuits which may damage the proper operation of the integrated circuit. To ensure proper operation of these devices under radiation, thorough testing must be made especially in critical applications like space and military applications. Although the standard which describes the procedure for testing electronic devices under radiation emphasizes the use of worst case test vectors (WCTVs), they are never used in radiation testing due to the difficulty of generating these vectors for circuits under test. For decades, design for testability (DFT) has been the best choice for test engineers to test digital circuits in industry. It has become a very mature technology that can be relied on. DFT is usually used with automatic test patterns generation (ATPG) software to generate test vectors to test application specific integrated circuits (ASICs), especially with sequential circuits, against faults like stuck at faults and path delay faults. Surprisingly, however, radiation testing has not yet made use of this reliable technology. In this thesis, a novel methodology is proposed to extend the usage of DFT to generate WCTVs for delay failure in Flash based field programmable gate arrays (FPGAs) exposed to total ionizing dose (TID). The methodology is validated using MicroSemi ProASIC3 FPGA and cobalt 60 facility

Chameleon: A Hybrid Secure Computation Framework for Machine Learning Applications

We present Chameleon, a novel hybrid (mixed-protocol) framework for secure function evaluation (SFE) which enables two parties to jointly compute a function without disclosing their private inputs. Chameleon combines the best aspects of generic SFE protocols with the ones that are based upon additive secret sharing. In particular, the framework performs linear operations in the ring $\mathbb{Z}_{2^l}$ using additively secret shared values and nonlinear operations using Yao's Garbled Circuits or the Goldreich-Micali-Wigderson protocol. Chameleon departs from the common assumption of additive or linear secret sharing models where three or more parties need to communicate in the online phase: the framework allows two parties with private inputs to communicate in the online phase under the assumption of a third node generating correlated randomness in an offline phase. Almost all of the heavy cryptographic operations are precomputed in an offline phase which substantially reduces the communication overhead. Chameleon is both scalable and significantly more efficient than the ABY framework (NDSS'15) it is based on. Our framework supports signed fixed-point numbers. In particular, Chameleon's vector dot product of signed fixed-point numbers improves the efficiency of mining and classification of encrypted data for algorithms based upon heavy matrix multiplications. Our evaluation of Chameleon on a 5 layer convolutional deep neural network shows 133x and 4.2x faster executions than Microsoft CryptoNets (ICML'16) and MiniONN (CCS'17), respectively

A Hardware Security Solution against Scan-Based Attacks

Scan based Design for Test (DfT) schemes have been widely used to achieve high fault coverage for integrated circuits. The scan technique provides full access to the internal nodes of the device-under-test to control them or observe their response to input test vectors. While such comprehensive access is highly desirable for testing, it is not acceptable for secure chips as it is subject to exploitation by various attacks. In this work, new methods are presented to protect the security of critical information against scan-based attacks. In the proposed methods, access to the circuit containing secret information via the scan chain has been severely limited in order to reduce the risk of a security breach. To ensure the testability of the circuit, a built-in self-test which utilizes an LFSR as the test pattern generator (TPG) is proposed. The proposed schemes can be used as a countermeasure against side channel attacks with a low area overhead as compared to the existing solutions in literature