Single-event effects on combinational logic circuits operating at ultra-low power

The minimum laser energy required to cause sustained harmonic oscillations in a 201-stage ring oscillator varies little with increasing power supply voltage when operating in the subthreshold region. These small changes in threshold laser energy in the subthreshold region suggest that the cross-section curves as a function of power supply voltage remain relatively constant. Simulations show that the minimum pulsewidth required to generate higher-order oscillations decreases as operating voltage increases. Single-event transients are wider when circuits are operating in the subthreshold region than when operating at the nominal power supply voltages. Narrower single-event transients result for strikes on PMOS transistors as compared to those for strikes on NMOS devices in the subthreshold region; the opposite is observed when circuits are operating at the nominal power supply voltages. Index Terms--CMOS circuits, digital circuits, radiation effects, radiation effects in ICs, single-event effects, single event transients.