A Delay-efficient Radiation-hard Digital Design Approach Using CWSP Elements

In this paper, we present a radiation-hardened digital design approach. This approach is based on the use of code word state preserving (CWSP) elements at each flip-flop of the design, and leaving the rest of the design unaltered. The CWSP element provides 100% SET protection for glitch widths up to min{D_min/2, (D_max - Delta)/2}, where D_min and D_max are the minimum and maximum circuit delay respectively and Delta is an extra delay associated with our SET protection circuit. The CWSP circuit has two inputs - the latch output signal and the same signal delayed by a quantity delta. In case an SET error is detected, then the current computation is repeated, using the correct output, which is generated later in the same clock period by the CWSP element. Unlike previous approaches, we use the CWSP element in a secondary path and the CWSP logic is designed to minimally impact the critical delay path of the design. The delay penalty of our approach (averaged over several designs) is less than 1%. Thus our technique is applicable for high-speed designs, where the additional delay associated with SET protection must be kept at a minimum.