The conventional ‘analog’ approach
Although photon counting is by definition a digital task, conventional silicon photomultipliers combine the electrical pulses generated by multiple photon detections into a single analog output signal. This signal has to be processed by expensive power-consuming electronics in order to recover the photon count.
The Philips ‘digital’ approach
By integrating low-power CMOS digital electronics into the silicon photomultiplier chip, the Digital Photon Counting team at Philips has developed a silicon photomultiplier in which each photon detection is converted directly into an ultra high speed digital pulse that can be directly counted by on-chip counter circuitry. In contrast to conventional silicon photomultipliers, Philips’ new silicon photomultipliers are therefore ‘all-digital’ (digital-in/digital-out) devices. As a result, they achieve faster and more accurate photon counting with extremely well defined timing of the first photon detection – both of which are important factors in applications such as medical imaging and high-energy nuclear physics.