Weak-conditioned Half Buffer Research Articles

Design of ACS Architecture Using FinFET and CNTFET Devices for Low-Power Viterbi Decoder Using Asynchronous Techniques for Digital Communication Systems

Viterbi algorithm is the most popular algorithm used to decode the convolution code, but its computational complexity increases exponentially with the increasing constraint length due to a large number of Trellis transitions. However, high constraint length is necessary to improve the accuracy of the decoding process for the high rate convolution code. In particular, the Add-Compare-Select (ACS) module of the Viterbi Decoder will have large numbers of trellis states and trellis transitions with increased constraint lengths, which give rise to high hardware complexity and large power consumption. As the performance of the Viterbi decoder mainly depends on its efficient implementation of the ACS module, in the literature, several methods are presented for the implementation of ACS for the Viterbi decoder. The methods based on Precharge Half Buffer (PCHB) and Weak Conditioned Half Buffer, Shannon’s decomposition circuits, body-biased pseudo-NMOS logic and Quasi Delay Insensitive (QDI) timing model performance is analyzed. The methods are implemented using CMOS technology. In this paper, FinFET and CNTFET-based ACS implementation is performed. From the analysis, it has been found that the Carbon Nanotube-based implementation is better in performance when compared to the CMOS and FinFET technology. The proposed QDI model and retiming circuits for ACS block operate above 1[Formula: see text]GHz with high driving current and low power.

A Data-Driven Asynchronous Neural Network Accelerator

Deep neural networks (DNNs) are revolutionizing machine learning, with unprecedented accuracy on many AI tasks. Energy-efficient neural acceleration is crucial in broadening DNN applications in cloud and mobile end devices. However, power-hungry clock networks limit the energy-efficiency of DNN accelerators. In this work, we propose a novel DNN hardware accelerator, called the asynchronous neural network processor (AsNNP). At the heart of AsNNP is a scalable hierarchy matrix multiply unit, with bit-serial processing elements working in parallel. It replaces the global clock networks with asynchronous handshake protocols to realize the synchronization and communication between each part, minimizing the dynamic power. Meanwhile, a fine-grain asynchronous pipeline based on weak-conditioned half-buffer (WCHB) is introduced to pipe successive computations in a data-driven manner, i.e., once data arrives computation begins, maximizing the throughput. These techniques enable AsNNP to work in a fully data-driven asynchronous communication fashion with optimized energy-efficiency. The proposed accelerator is implemented with quasi-delay-insensitive (QDI) clockless logic family and evaluated in a 65 nm process. Compared with the synchronous baseline, simulation results show that AsNNP offers 2.2× higher equivalent frequency and 1.59× lower power. Compared with state-of-the-art DNN accelerators, AsNNP shows 1.17×-4.97× energy-efficiency improvement.

Design of an MTJ/CMOS-Based Asynchronous System for Ultra-Low Power Energy Autonomous Applications

Most of today’s IoT-based computing systems offer an opportunity to build smarter systems for application areas such as healthcare monitoring and wireless sensor nodes. Since these systems are energy limited and remain idle for most of the time, they suffer from large leakage power dissipation. Another problem faced by such computing systems is sporadic power failures when employed with energy harvesters where the system loses its current state and needs long reinitialization time. To address these problems, this work combines asynchronous design techniques with nonvolatility to achieve ultra-low power operation during active mode and data retention during power failure. This paper first presents a detailed analysis of different implementations of volatile c-element and compares their performance in terms of power and delay. Then one of the implementations is selected for nonvolatile design of a hybrid c-element using emerging spin transfer torque–magnetic tunnel junction (STT–MTJ) technology which allows energy-efficient data retention during idle mode/power-off mode and during sudden power failures. Using this hybrid c-element, we design a novel nonvolatile weak conditioned half-buffer. The extensive analysis of these designs with different design metrics is performed at the circuit level using Synopsys HSPICE circuit simulator.

Scalable Synthesis of PCHB–WCHB Hybrid Quasi-Delay Insensitive Circuits

The increasing cost paid in clocking integrated circuits and combating timing variations forces designers to rethink asynchronous approaches to system realization. Among various techniques, quasi-delay insensitive design is promising due to its very relaxed timing assumption. Its expensive logic overhead, however, often nullifies its promise of performance and power improvements, and remains a major obstacle on the way of its adoption. To overcome this obstacle, this paper proposes an efficient static performance analysis procedure and a synthesis flow for precharged half buffer and weak-conditioned half buffer circuit optimization. Experimental results demonstrate efficient performance analysis and effective area reduction under pipeline cycle time constraints.

Low power sub‐threshold asynchronous quasi‐delay‐insensitive 32‐bit arithmetic and logic unit based on autonomous signal‐validity half‐buffer

The authors propose an asynchronous-logic (async) quasi-delay-insensitive (QDI) autonomous signal-validity half-buffer (ASVHB) realisation approach for low power sub-threshold operation (V DD = 0.2 V). There are three key attributes in the proposed ASVHB realisation approach. First, the ASVHB realisation approach embodies integrated autonomous validity signals, which are unique and are used exclusively to simplify the circuit implementation for QDI protocol. Second, the ASVHB realisation approach applies the fine-grained gate-level method, which propagates data through a single-cell datapath pipeline to maximise the throughput rate. Third, the ASVHB realisation approach adopts the static-logic implementation, which maintain stable output states (by connecting them directly to the power rails), to feature high robustness for sub-threshold operation. They compare their ASVHB realisation approach against the competitive reported weak-conditioned half-buffer (WCHB) and pre-charged half-buffer (PCHB) realisation approaches. The WCHB and PCHB library cells, on average, require ∼2.1 × and ∼1.9 × more transistors than the ASVHB library cells. With respect to a 3-stage pipeline realisation, the WCHB and PCHB pipelines, on average, require 1.8 × and 1.5× more transitions per-cycle than the ASVHB pipeline. They design an async 32-bit arithmetic and logic unit (ALU) based on the proposed ASVHB realisation approach (at 65 nm CMOS process). Their ASVHB ALU occupies 0.092 mm2, and in many merits, outperforms the WCHB and PCHB counterparts. The WCHB and PCHB counterparts require ∼1.7 × and ∼1.4× more transistors, respectively, than their design. At the sub-threshold voltage of V DD = 0.2 V, the WCHB and PCHB counterparts dissipate ∼1.7× and ∼2.6× more energy, respectively, and are, respectively, ∼0.95× and ∼0.73× slower throughput.

An Asynchronous Low Power and High Performance VLSI Architecture for Viterbi Decoder Implemented with Quasi Delay Insensitive Templates.

Convolutional codes are comprehensively used as Forward Error Correction (FEC) codes in digital communication systems. For decoding of convolutional codes at the receiver end, Viterbi decoder is often used to have high priority. This decoder meets the demand of high speed and low power. At present, the design of a competent system in Very Large Scale Integration (VLSI) technology requires these VLSI parameters to be finely defined. The proposed asynchronous method focuses on reducing the power consumption of Viterbi decoder for various constraint lengths using asynchronous modules. The asynchronous designs are based on commonly used Quasi Delay Insensitive (QDI) templates, namely, Precharge Half Buffer (PCHB) and Weak Conditioned Half Buffer (WCHB). The functionality of the proposed asynchronous design is simulated and verified using Tanner Spice (TSPICE) in 0.25 µm, 65 nm, and 180 nm technologies of Taiwan Semiconductor Manufacture Company (TSMC). The simulation result illustrates that the asynchronous design techniques have 25.21% of power reduction compared to synchronous design and work at a speed of 475 MHz.