Binary Addition in Resistance Switching Memory Array by Sensing Majority

The flow of data between processing and memory units in contemporary computing systems is their main performance and energy-efficiency bottleneck, often referred to as the ‘von Neumann bottleneck’ or ‘memory wall’. Emerging resistance switching memories (memristors) show promising signs to overcome the ‘memory wall’ by enabling computation in the memory array. Majority logic is a type of Boolean logic, and in many nanotechnologies, it has been found to be an efficient logic primitive. In this paper, a technique is proposed to implement a majority gate in a memory array. The majority gate is realised in an energy-efficient manner as a memory READ operation. The proposed logic family disintegrates arithmetic operations to majority and NOT operations which are implemented as memory READ and WRITE operations. A 1-bit full adder can be implemented in 6 steps (memory cycles) in a 1T–1R array, which is faster than IMPLY , NAND , NOR and other similar logic primitives

Power Profile Obfuscation using RRAMs to Counter DPA Attacks

Side channel attacks, such as Differential Power Analysis (DPA), denote a special class of attacks in which sensitive key information is unveiled through information extracted from the physical device executing a cryptographic algorithm. This information leakage, known as side channel information, occurs from computations in a non-ideal system composed of electronic devices such as transistors. Power dissipation is one classic side channel source, which relays information of the data being processed. DPA uses statistical analysis to identify data-dependent correlations in sets of power measurements. Countermeasures against DPA focus on hiding or masking techniques at different levels of design abstraction and are typically associated with high power and area cost. Emerging technologies such as Resistive Random Access Memory (RRAM), offer unique opportunities to mitigate DPAs with their inherent memristor device characteristics such as variability in write time, ultra low power (0.1-3 pJ/bit), and high density (4F2). In this research, an RRAM based architecture is proposed to mitigate the DPA attacks by obfuscating the power profile. Specifically, a dual RRAM based memory module masks the power dissipation of the actual transaction by accessing both the data and its complement from the memory in tandem. DPA attack resiliency for a 128-bit AES cryptoprocessor using RRAM and CMOS memory modules is compared against baseline CMOS only technology. In the proposed AES architecture, four single port RRAM memory units store the intermediate state of the encryption. The correlation between the state data and sets of power measurement is masked due to power dissipated from inverse data access on dual RRAM memory. A customized simulation framework is developed to design the attack scenarios using Synopsys and Cadence tool suites, along with a Hamming weight DPA attack module. The attack mounted on a baseline CMOS architecture is successful and the full key is recovered. However, DPA attacks mounted on the dual CMOS and RRAM based AES cryptoprocessor yielded unsuccessful results with no keys recovered, demonstrating the resiliency of the proposed architecture against DPA attacks

Embedding Logic and Non-volatile Devices in CMOS Digital Circuits for Improving Energy Efficiency

abstract: Static CMOS logic has remained the dominant design style of digital systems for more than four decades due to its robustness and near zero standby current. Static CMOS logic circuits consist of a network of combinational logic cells and clocked sequential elements, such as latches and flip-flops that are used for sequencing computations over time. The majority of the digital design techniques to reduce power, area, and leakage over the past four decades have focused almost entirely on optimizing the combinational logic. This work explores alternate architectures for the flip-flops for improving the overall circuit performance, power and area. It consists of three main sections. First, is the design of a multi-input configurable flip-flop structure with embedded logic. A conventional D-type flip-flop may be viewed as realizing an identity function, in which the output is simply the value of the input sampled at the clock edge. In contrast, the proposed multi-input flip-flop, named PNAND, can be configured to realize one of a family of Boolean functions called threshold functions. In essence, the PNAND is a circuit implementation of the well-known binary perceptron. Unlike other reconfigurable circuits, a PNAND can be configured by simply changing the assignment of signals to its inputs. Using a standard cell library of such gates, a technology mapping algorithm can be applied to transform a given netlist into one with an optimal mixture of conventional logic gates and threshold gates. This approach was used to fabricate a 32-bit Wallace Tree multiplier and a 32-bit booth multiplier in 65nm LP technology. Simulation and chip measurements show more than 30% improvement in dynamic power and more than 20% reduction in core area. The functional yield of the PNAND reduces with geometry and voltage scaling. The second part of this research investigates the use of two mechanisms to improve the robustness of the PNAND circuit architecture. One is the use of forward and reverse body biases to change the device threshold and the other is the use of RRAM devices for low voltage operation. The third part of this research focused on the design of flip-flops with non-volatile storage. Spin-transfer torque magnetic tunnel junctions (STT-MTJ) are integrated with both conventional D-flipflop and the PNAND circuits to implement non-volatile logic (NVL). These non-volatile storage enhanced flip-flops are able to save the state of system locally when a power interruption occurs. However, manufacturing variations in the STT-MTJs and in the CMOS transistors significantly reduce the yield, leading to an overly pessimistic design and consequently, higher energy consumption. A detailed analysis of the design trade-offs in the driver circuitry for performing backup and restore, and a novel method to design the energy optimal driver for a given yield is presented. Efficient designs of two nonvolatile flip-flop (NVFF) circuits are presented, in which the backup time is determined on a per-chip basis, resulting in minimizing the energy wastage and satisfying the yield constraint. To achieve a yield of 98%, the conventional approach would have to expend nearly 5X more energy than the minimum required, whereas the proposed tunable approach expends only 26% more energy than the minimum. A non-volatile threshold gate architecture NV-TLFF are designed with the same backup and restore circuitry in 65nm technology. The embedded logic in NV-TLFF compensates performance overhead of NVL. This leads to the possibility of zero-overhead non-volatile datapath circuits. An 8-bit multiply-and- accumulate (MAC) unit is designed to demonstrate the performance benefits of the proposed architecture. Based on the results of HSPICE simulations, the MAC circuit with the proposed NV-TLFF cells is shown to consume at least 20% less power and area as compared to the circuit designed with conventional DFFs, without sacrificing any performance.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201