Ring oscillator based clock generation for a radiation-hardened optically reconfigurable gate array VLSI

Currently available radiation-hardened very large scale integrated circuits (VLSIs) are extremely vulnerable to radiation. Assuming nuclear power plant maintenance and decommissioning situations as examples, the radiation tolerance of current radiation-hardened VLSIs is insufficient in terms both of the total-ionizing-dose and soft-error tolerances. Therefore, we continued development of radiation-hardened optically reconfigurable gate arrays with 1 Grad total-ionizing-dose tolerance, which is about 1000 times higher radiation tolerance than current typical radiation-hardened VLSIs. However, even for optically reconfigurable gate arrays, any digital circuit must function based on a clock signal generated by a crystal oscillator. Nevertheless, crystal oscillator circuits are irreparably damaged easily by radiation as are current VLSIs. To realize a higher radiation tolerant system using a radiation-hardened optically reconfigurable gate array, the radiation tolerance of a clock source must be increased. This paper presents dependable ring oscillator based clock generation on an optically reconfigurable gate array VLSI and its related experimentally obtained results.