Comparison of error rates in combinational and sequential logic

A pulsed laser was used to demonstrate that, for transients much shorter than the clock period, error rates in sequential logic were independent of frequency, whereas error rates in combinational logic were linearly dependent on frequency. In addition, by measuring the error rate as a function of laser pulse energy for fixed clock frequency, the logarithmic dependence of the SEU vulnerable time period prior to the clock edge in combinational logic was established. A mixed mode circuit simulator program was used to successfully model the dynamic response of the logic circuit to pulses of laser light.