Redundant Logic Insertion and Fault Tolerance Improvement in Combinational Circuits

This paper presents a novel method to identify and insert redundant logic into a combinational circuit to improve its fault tolerance without having to replicate the entire circuit as is the case with conventional redundancy techniques. In this context, it is discussed how to estimate the fault masking capability of a combinational circuit using the truth-cum-fault enumeration table, and then it is shown how to identify the logic that can introduced to add redundancy into the original circuit without affecting its native functionality and with the aim of improving its fault tolerance though this would involve some trade-off in the design metrics. However, care should be taken while introducing redundant logic since redundant logic insertion may give rise to new internal nodes and faults on those may impact the fault tolerance of the resulting circuit. The combinational circuit that is considered and its redundant counterparts are all implemented in semi-custom design style using a 32/28nm CMOS digital cell library and their respective design metrics and fault tolerances are compared

Mathematical Estimation of Logical Masking Capability of Majority/Minority Gates Used in Nanoelectronic Circuits

In nanoelectronic circuit synthesis, the majority gate and the inverter form the basic combinational logic primitives. This paper deduces the mathematical formulae to estimate the logical masking capability of majority gates, which are used extensively in nanoelectronic digital circuit synthesis. The mathematical formulae derived to evaluate the logical masking capability of majority gates holds well for minority gates, and a comparison with the logical masking capability of conventional gates such as NOT, AND/NAND, OR/NOR, and XOR/XNOR is provided. It is inferred from this research work that the logical masking capability of majority/minority gates is similar to that of XOR/XNOR gates, and with an increase of fan-in the logical masking capability of majority/minority gates also increases

Timing models for high-level synthesis

In this paper, we describe a timing model for clock estimation during high-level synthesis. In order to obtain realistic timing estimates, the proposed model considers all delay elements, including datapath, control and wire delays, and several technology factors, such as layout architecture, technology mapping, buffers insertion and loading effects. The experimental results show that this model can provide much better estimates than previous models. This model is well suited for automatic and interactive synthesis as well as feedback-driven synthesis where performance matrices must be rapidly and incrementally calculated

Latency Optimized Asynchronous Early Output Ripple Carry Adder based on Delay-Insensitive Dual-Rail Data Encoding

Asynchronous circuits employing delay-insensitive codes for data representation i.e. encoding and following a 4-phase return-to-zero protocol for handshaking are generally robust. Depending upon whether a single delay-insensitive code or multiple delay-insensitive code(s) are used for data encoding, the encoding scheme is called homogeneous or heterogeneous delay-insensitive data encoding. This article proposes a new latency optimized early output asynchronous ripple carry adder (RCA) that utilizes single-bit asynchronous full adders (SAFAs) and dual-bit asynchronous full adders (DAFAs) which incorporate redundant logic and are based on the delay-insensitive dual-rail code i.e. homogeneous data encoding, and follow a 4-phase return-to-zero handshaking. Amongst various RCA, carry lookahead adder (CLA), and carry select adder (CSLA) designs, which are based on homogeneous or heterogeneous delay-insensitive data encodings which correspond to the weak-indication or the early output timing model, the proposed early output asynchronous RCA that incorporates SAFAs and DAFAs with redundant logic is found to result in reduced latency for a dual-operand addition operation. In particular, for a 32-bit asynchronous RCA, utilizing 15 stages of DAFAs and 2 stages of SAFAs leads to reduced latency. The theoretical worst-case latencies of the different asynchronous adders were calculated by taking into account the typical gate delays of a 32/28nm CMOS digital cell library, and a comparison is made with their practical worst-case latencies estimated. The theoretical and practical worst-case latencies show a close correlation....Comment: arXiv admin note: text overlap with arXiv:1704.0761

Asynchronous Early Output Dual-Bit Full Adders Based on Homogeneous and Heterogeneous Delay-Insensitive Data Encoding

This paper presents the designs of asynchronous early output dual-bit full adders without and with redundant logic (implicit) corresponding to homogeneous and heterogeneous delay-insensitive data encoding. For homogeneous delay-insensitive data encoding only dual-rail i.e. 1-of-2 code is used, and for heterogeneous delay-insensitive data encoding 1-of-2 and 1-of-4 codes are used. The 4-phase return-to-zero protocol is used for handshaking. To demonstrate the merits of the proposed dual-bit full adder designs, 32-bit ripple carry adders (RCAs) are constructed comprising dual-bit full adders. The proposed dual-bit full adders based 32-bit RCAs incorporating redundant logic feature reduced latency and area compared to their non-redundant counterparts with no accompanying power penalty. In comparison with the weakly indicating 32-bit RCA constructed using homogeneously encoded dual-bit full adders containing redundant logic, the early output 32-bit RCA comprising the proposed homogeneously encoded dual-bit full adders with redundant logic reports corresponding reductions in latency and area by 22.2% and 15.1% with no associated power penalty. On the other hand, the early output 32-bit RCA constructed using the proposed heterogeneously encoded dual-bit full adder which incorporates redundant logic reports respective decreases in latency and area than the weakly indicating 32-bit RCA that consists of heterogeneously encoded dual-bit full adders with redundant logic by 21.5% and 21.3% with nil power overhead. The simulation results obtained are based on a 32/28nm CMOS process technology