Towards Resilient Quasi Delay Insensitive Conditional Control Elements

Abstract

The causal behavior of Quasi Delay-Insensitive (QDI) circuits may get compromised under the effects of single event transients (SETs). To address the issue, the research community already made efforts in different directions, like with modular redundancy, or shortening the data accepting windows of buffer templates. Nevertheless, in non-modular techniques, the focus remains towards the buffers and combinational logic. Most of the time the conditional control elements, namely Multiplexer and De-multiplexer, are not explicitly addressed. However, for the event-driven behavior these elements are also realized with a storage element called Muller C-element (MCE), so in principle these elements also require special consideration to improve the overall fault tolerance of the circuit. In this article we first analyze the error contribution of these elements during single event transient (SET) strikes and then present a hardening technique to mitigate these effects. The focus is to utilize the inherent fault-tolerance properties of QDI circuits. For better coverage of scenarios we test our technique with two different target circuits, an 8-bit Arithmetic Logic Unit (ALU) circuit designed in a simple linear fashion and a 16-bit iterative multiplier. The analysis includes the state-of-the-art buffer template with one of its SET hardened derivatives named Zeta. The findings suggest 40% improvement in tolerance towards SETs with Zeta_E, our proposed template with resilient conditional control elements.