In this new Application Note we focus our attention on the techniques for time measurement using waveform Digitizer. It describes the algorithms typically used for these measurements and the performances obtained in some benchmark tests using different acquistion setup. This note shows that Digitizers are capable to measure time stamps with higher accuracy (few ps resolution) compared to commercial analog solution composed by CFD and TDC modules.
Traditional analog devices as the Constant Fraction Discriminators (CFDs) and Time to Digital Converters (TDCs) can be very competitive in terms of channel density and cost. Highly segmented detectors are therefore often read out by analog devices featuring custom made specification to guarantee a perfect match with the experimental requirements. However the possible requirement of simultaneous measurement of energy and time poses the practical issue of complex device connections.
In some applications the implementation of a digitizer for time measurements is profitable or even necessary:
Traditional analog devices as the Constant Fraction Discriminators (CFDs) and Time to Digital Converters (TDCs) can be very competitive in terms of channel density and cost. Highly segmented detectors are therefore often read out by analog devices featuring custom made specification to guarantee a perfect match with the experimental requirements. However the possible requirement of simultaneous measurement of energy and time poses the practical issue of complex device connections.
In some applications the implementation of a digitizer for time measurements is profitable or even necessary:
- Applications that require an excellent timing resolution of the whole chain, of the order of few ps
- Simultaneous acquisition of time and energy information
- Online walk correction with integrated charge or amplitude
- Bursts of very close pulses (e.g. Free Electron Lasers)
In the note a brief description of the digital CFD (dCFD) method and the contributions to the time measurement uncertainty will be provided together with the measurements description. They were performed using a Plastic Scintillators coupled with Photomultiplier Tubes, an Arbitrary Function Generator and a Setup with Silicon Pixel detectors together with the following CAEN digitizer families:
The algorithms described can be easily embedded into the data acquisition software and provide accurate time measurements, which can reach few picosecond resolution. Digitizers are capable to measure time stamps with higher accuracy compared to commercial analog solution composed by CFD and TDC modules. This difference in time resolution emerges significantly when experimental setup have low time jitter between pulses, of the order of some tens of picoseconds. Also the switching capacitor technology is highly competitive in terms of cost and provide performances comparable to fast ADC chips, but at present time can be limited by analog to digital conversion dead time.
