Multi-Peak Mode

As pointed out in section , p. , the APV Sequencer is able to generate a programmable trigger pattern which is issued either by software or hardware trigger. Together with the multi-peak mode of the APV25, this feature can be used to effectively obtain subsequent samples of the shaping curve from a particle signal.

Figure: Screenshot of the raw APV25 output with consecutive samples obtained with a trigger sequence in multi-peak mode, representing a single particle hit.

Fig.  shows an example of the APV25 output in this mode. Four triggers separated by $75\,\rm ns$ are sent to the APV25, which returns three consecutive samples after each trigger, resulting in a total of twelve sequential samples, revealing the (negative) pulse shape. The average waveform obtained from this measurement matches with the peak mode pulse shape scanned by internal calibration.

A pulse shape fit has been applied to every multi-event, returning the peaking time position. With the normal scintillator trigger, the distribution of these peaking times are an indicator for the quality of timing and synchronization. As shown in fig. , an RMS peaking time spread of $2\,\rm ns$ was obtained, including beam fluctuations, the timing jitter and the fit error.

Figure: APV25 peaking time distribution with scintillator trigger at low intensity.

Figure: APV25 peaking time distribution with random trigger at high intensity, revealing the $20\,\rm ns$ PSI beam period.

The same measurement was repeated at high intensity with random triggering. With the APV25 still clocked at the nominal $40\,\rm MHz$, the PSI beam structure of $50\,\rm MHz$ (corresponding to $20\,\rm ns$) is visualized (fig. ). The pulse shape fit does not always converge. With a later peak, less signal samples are contained within the measurement window, making the fit procedure more difficult. Fits which did not converge were not included in this plot, leading to fewer entries with increasing peaking times, although the peaking times are evenly distributed over the full scale.