Fully differential charge to time converter and fast shaper readout circuit with gain compensation for SiPM

The implementation of fully differential readout method for Silicon Photomultipliers (SiPM) is presented. The front-end circuit consists of preamplifier with fast shaper and Charge to Time Converter (QTC). The fast shaper generates unipolar pulse. The peaking time for single photoelectron is equal to 3.6ns and the FWHM is 3.8ns. The pulse width of the QTC depends on the number of photons. The gain of SiPM is compensated by moderating the bias voltage. The polarization voltage is adjusted indirectly by tuning the output common mode voltage (VOCM) of fully differential amplifier. The advantage of the algorithm is the possibility to set the bias of each SiPM in the array independently so they all could operate in similar conditions (have similar gain and dark count rate).