Circuit and method for fluorescence lifetime imaging

A detection system for detecting fluorescence lifetime, the detection system comprising:

• an excitation light source configured for repeatedly generating pulsed excitation light, and a detector comprising:
• a single-photon detection circuit for generating digital pulses upon detection of photons,
• a pulse-inhibit circuit for rejecting detected photons that occur outside each one of a series of measurement time windows, each subsequent measurement time window starting after a subsequent excitation light pulse has stopped and stopping before a next excitation light pulse is generated, each measurement time window having a measurement window period,
• a first switched-capacitor circuit having an input terminal for receiving a voltage ramp signal that is restarted with each new measurement window period, the first switched-capacitor circuit being configured for repetitively computing an average voltage, based on an exponential moving average function applied to sample voltages recorded over past measurement time windows and determined by the voltage ramp signal in response to detected and not rejected photons, following the principles of the center-of-mass method, the first switched-capacitor circuit having a first node for outputting the computed average voltage as a measure of the fluorescence lifetime.