ISSW 2026

We present a fully electrical SPAD-based QRNG using an on-chip trigger diode. Unlike LED-illuminated SPAD QRNGs, the trigger diode is used to initiate SPAD events while enabling electrical tuning of the event rate. An X-FAB XH018 test chip includes SPADs with 10 µm and 20 µm active diameters, each with and without metal shielding, and an active quench circuit. Timestamps are recorded with an external time-tagging. The random bit stream is created by comparing the consecutive inter-arrival times of successive pulses. Randomness is assessed with NIST SP 800-90B. At matched count rates several decades above dark count, a special operating condition B yields entropy comparable to diffuse optical excitation, whereas dark-count-only and a different operating condition A show notably reduced randomness.