LASER CONFIRMATION OF SEU EXPERIMENTS IN GAAS-MESFET COMBINATIONAL LOGIC

Majority vote and self-scrubbing circuitry were utilized to harden the registers of a GaAs logic circuit to single event upsets (SEU). Ion beam testing of the hardened part at low scrub frequencies showed fewer system upsets than an unhardened part. At high frequencies the upset rate increased with frequency, indicating a clock-dependent SEU sensitive node. A pulsed laser was used to identify an input node in the self-scrubbing circuitry as being the source of the upsets at high frequencies. Because the node was only sensitive for a short duration prior to the rising clock edge, more clock-edge dependent SEUs could occur at higher frequencies. The relative SEU thresholds of the registers and the input node measured with the laser showed excellent agreement with ion data. All single point SEU failure nodes were identified and their upset thresholds measured. With this information it was possible to redesign the circuit to reduce its sensitivity to SEU at high scrub frequencies.