Broadcom'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 Broadcom 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 single SPAD |
| IPulse | = | Internal current source representing Geiger discharge |
| Rq | = | Quenching resistor |
| Cq | = | Parasitic quenching capacitance |
| Cg | = | Stray capacitance of the grid, i.e. all electrical traces |
| RS | = | Series resistance |
The time constant of the leading signal edge (rise time) is below 1ns for Broadcom NUV-MT SiPMs and is determined by the Capacitance of the fired SPAD(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 SPAD 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)
A useful attribute of SiPMs in some applications is that the fast frequency components can be extracted using a high-pass filter. The plot below shows, in black, the pulse shape acquired from a single SiPM on an AFBR-S4N44P164M (4x4 array, 4mm pitch) readout over 25Ω after irradiation with a short laser pulse and demonstrates that with a recharge time of 55ns the signal returns to zero at ~275ns (i.e. ~5x Tau). The red pulse shows the fast frequency components using >200MHz high-pass filter and demonstrates a time constant of only 9ns.
In applications such as Time Of Flight Positron Emission Tomography (TOF-PET) and LiDAR (Light Detection and Ranging, or Laser Imaging, Detection & Ranging) the fast pulse can be extremely beneficial but it should be noted that:-
- Extracting the AC-coupled signal does not change the intrinsic recharge time and so may lead to a rate-dependent signal amplitude due to signal pile up.
- The SiPM signal recharge time is proportional to the quenching resistance and the parasitic capacitances of the quenching resistor and the grid.
- The load resistor with the capacitances of the grid and the inactive SPADs may act as a low-pass filter and prolong the observed signal decay time but WILL NOT change the intrinsic recharge time of the SiPM.
Broadcom have produced a number of helpful application notes including Working with Broadcom SiPMs which discusses the issues highlighted in this article. This and other application notes can be accessed below
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Broadcom's SiPM Family overview |
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Product Brief, NUV-MT SiPM range |
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A Brief Introduction to SiPMs |
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Working with Broadcom SiPMs |
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SiPM Dynamic Range, Linearity and Saturation |
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NUV-MT Performance Correlation |
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NUV-MT Single-Photon Measurements |
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SiPM Characteristics for PMT Users |
For more detail please visit the Support pages using the links in this article and on the right hand side of this page.
