The present specification describes an improved multi-energy radiation detector. In one embodiment, the signal generated by the detection medium is converted to digital form directly at the point of signal collection. This avoids the need for power intensive high bandwidth amplifiers and analog-to-digital converters, as it integrates the sensing device and signal processing onto the same silicon substrate to reduce the number of components in the system. In one embodiment, a single photon avalanche diode (SPAD) is coupled directly to a threshold detector to achieve an intrinsically low power and low noise detector.