Compact CMOS active quenching/recharge circuit for SPAD arrays

Abstract

Avalanche diodes operating in Geiger mode are able to detect single photon events. They can be employed to photon counting and time-of-flight estimation. In order to ensure proper operation of these devices, the avalanche current must be rapidly quenched, and, later on, the initial equilibrium must be restored. In this paper, we present an active quenching/recharge circuit specially designed to be integrated in the form of an array of single-photon avalanche diode (SPAD) detectors. Active quenching and recharge provide benefits like an accurately controllable pulse width and afterpulsing reduction. In addition, this circuit yields one of the lowest reported area occupations and power consumptions. The quenching mechanism employed is based on a positive feedback loop that accelerates quenching right after sensing the avalanche current. We have employed a current starved inverter for the regulation of the hold-off time, which is more compact than other reported controllable delay implementations. This circuit has been fabricated in a standard 0.18 μm complementary metal-oxide-semiconductor (CMOS) technology. The SPAD has a quasi-circular shape of 12 μm diameter active area. The fill factor is about 11%. The measured time resolution of the detector is 187 ps. The photon-detection efficiency (PDE) at 540 nm wavelength is about 5% at an excess voltage of 900 mV. The break-down voltage is 10.3 V. A dark count rate of 19 kHz is measured at room temperature. Worst case post-layout simulations show a 117 ps quenching and 280 ps restoring times. The dead time can be accurately tuned from 5 to 500 ns. The pulse-width jitter is below 1.8 ns when dead time is set to 40 ns.