Figure 144 in the book shows the schematic diagram for our d.i.y. passively-quenched SPCM based on a Perkin-Elmer C30902S-DTC SPAD.
In our circuit, the SPAD is reverse-biased through a 200kΩ resistor. This value is sufficiently large that an avalanche in the SPAD will be quenched by itself within less than a nanosecond. The pulses produced by the SPAD are AC-coupled to a fast constant-level discriminator which has an output that is compatible with TTL logic circuits. Continue reading