KETEK's SiPM data sheets detail key performance parameters of their silicon photomultipliers including the rise and fall times which are discussed here in more detail.
The pulse shape of KETEK SiPMs is asymmetric due to the fact that the discharging and recharging procedure of a fired SiPM microcell is determined by different RC values.
This behaviour can be represented by an electrical model proposed by F. Corsi et. al. in “Modelling a silicon photomultiplier (SiPM) as a signal source for optimum front-end design.” (DOI 10.1016/j.nima.2006.10.219) with the following single components:-
|CD||=||Capacitance of the microcell|
|IPulse||=||Internal current source representing the Geiger discharge|
|CQ||=||Parasitic quenching capacitance|
|CG||=||Stray capacitance of all electrical traces|
The time constant of the leading signal edge (rise time) is below 1 ns for KETEK SiPMs and is determined by the Capacitance of the fired microcell(s) and the Series Resistance:-
Taurise = RS • CD
The signal tail has two different time constants:
A slow one which is determined by the quenching resistor and the microcell capacitances:-
TauD = RQ • (CD + CQ)
A fast one which is determined by the series resistance, the parasitic quenching capacitance and the parasitic grid capacitance. It is only visible as long as the series resistance is small enough.
TauF = RS • (CQ + CG)
The pulse shape of PM3315-WB and PM3325-WB SiPMs is shown measured with a 5Ω series / load resistor along with the exponential fits for the fast and the slow component. The signal rise time is clearly below 1 ns.