DAQ Golden Rules in the Anti-Aliasing Bessel Filter vs. Potentially Lost Events in the Surface Detectors in Cosmic Rays Experiments

The paper discusses the consequence of a standard approach (known as “Golden Rules”) to data acquisition for any surface detector of the cosmic rays experiments. When digitizing the analog signal, the spectrum is usually cut-off according to the Nyquist theorem. The cut-off frequency is set on a half of the sampling frequency. This approach allows avoiding aliasing effects. Nevertheless, if the signals, which we expect to detect, are very short with fast attenuated tails the anti-aliasing filter may dramatically reduce their amplitudes which in consequence may violate the standard trigger conditions. We analyzed large numbers of ADC traces detected by the prototype Front-End Board (FEB) based on the CycloneV FPGA 5CEFA9F31I7. The prototype FEB was not equipped with the anti-aliasing filter. We compared the original traces with filtered off-line in MATLAB. We see that a non-negligible number of events may be lost if the anti-aliasing hardware filter is implemented on the FEB.