A system-on-a-chip (SOC) within a package includes a reference generator, a matching circuit, a programmable current generator, a PWM controller, an overvoltage/undervoltage detector receiving a high voltage from a third output pad, a multiplexer passing an input signal to a second output pad, and a SPAD receiving the high voltage. Switching circuitry includes a first switch between the reference generator and an input of the programmable current generator, a second switch between the input of the current generator and the output of the matching circuit, a third switch between the reference generator and an input of the matching circuit, a fourth switch between an output of the current generator and a tap of a ladder within the overvoltage/undervoltage detector, a fifth switch between an output of the current generator and the first output pad, and a sixth switch between the output of the PWM controller and the first output pad.