A high bandwidth preamplifier for SiPM-based TOF PET scintillation detectors

In a Silicon Photomultiplier (SiPM) several hundreds or thousands of Geiger Mode Avalanche Photodiodes (GM APDs) are connected in parallel so as to combine the photon counting capabilities of these so-called microcells into a proportional light sensor. SiPM-based scintillation detectors can exhibit inherent nonlinearity, which may result in a degradation of the energy and position resolution. One cause of nonlinearity is saturation, which depends on the ratio between the total number of GM APDs that compose the device and the average number of photoelectrons created within the active volume of the SiPM during the recovery time of the cells. A second cause becomes apparent if we investigate the simultaneous firing of multiple cells. We show by means of Spice simulations that the output impedance of a SiPM changes with the number of fired cells. This introduces nonlinearity in the measured signal if the input impedance of subsequent front-end electronics is not negligible. To tackle this problem we present a new SiPM preamplifier design for SiPM based TOF PET scintillation detectors. A compact 16-channel front-end board for read-out of position-sensitive SiPM arrays has been built, based on this preamplifier concept. Our simulations and measurements show (i) excellent linearity, (ii) sufficiently low noise (∼85 fC referred to input) and (iii) outstanding low timing jitter (∼17 ps FWHM coincidence response of two SiPM’s excited by a laser pulse).