20
2 Front-End Electronics
2.3.3.3 Data Compression Using Zero Suppression
Compression of the sampled data is done by suppressing values below a certain
threshold, leaving only cluster data. The remaining data is then run-length encoded.
This method is highly dependent on having a stable baseline to achieve good compression and minimal loss of information, so different forms of digital signal conditioning are needed, depending on the detector. The compression is a lossy technique
as small signals or parts of signals might be lost. The achievable compression ratio
for gas-based detectors with a shaping front-end is generally inversely proportional
to the detector occupancy [21].
2.3.3.4 Baseline Correction
Due to manufacturing variations, there will be channel-to-channel and chip-to-chip
variations in the offset value of the analogue front-end outputs. This is commonly
referred to as a channels baseline or pedestal value. To avoid that this value is below
the lower operating range of the ADC, and to be able to include slight undershoots
in the tail of the pulse in the digitized data, a small positive offset is added in the
analogue front-end before the digital conversion. As the offset will vary from channel
to channel, it should be subtracted in the digital domain so that the pulses can be
accurately reconstructed later in the analysis.
The distribution of the baseline for each channel in the detector is determined in a
dedicated data-taking run, where no collisions occur, so that only the fixed baseline
and the superimposed noise can be measured. The average value of the distribution is
used for the baseline subtraction and the deviation is used to set the zero suppression
level.
2.3.3.5 Power Consumption
Both the TPC and MCH are planning to reuse the existing cooling system, power
supplies and power routing that is already in place. The TPC uses a water-cooled
copper envelope on the front-end card to keep the temperature of the detector close
to 21
◦ C. For the TPC the existing cooling can handle up to 35 mW/ch whereas the
power supply and distribution for the MCH is limited to about 13 mW/ch.
2.3.3.6 Slow-Control
Assuming the default start-up configuration of the device is defined with settings that
are close to what the TPC and MCH requires, there would not be a need to do many
configuration changes after the device has cold booted. For this reason, a low-speed
configuration is sufficient. The simplest option is to use I
2 C (Inter-Integrated Circuit)
as it provides multi-drop communication both ways using only two signal, which
2 Front-End Electronics
2.3.3.3 Data Compression Using Zero Suppression
Compression of the sampled data is done by suppressing values below a certain
threshold, leaving only cluster data. The remaining data is then run-length encoded.
This method is highly dependent on having a stable baseline to achieve good compression and minimal loss of information, so different forms of digital signal conditioning are needed, depending on the detector. The compression is a lossy technique
as small signals or parts of signals might be lost. The achievable compression ratio
for gas-based detectors with a shaping front-end is generally inversely proportional
to the detector occupancy [21].
2.3.3.4 Baseline Correction
Due to manufacturing variations, there will be channel-to-channel and chip-to-chip
variations in the offset value of the analogue front-end outputs. This is commonly
referred to as a channels baseline or pedestal value. To avoid that this value is below
the lower operating range of the ADC, and to be able to include slight undershoots
in the tail of the pulse in the digitized data, a small positive offset is added in the
analogue front-end before the digital conversion. As the offset will vary from channel
to channel, it should be subtracted in the digital domain so that the pulses can be
accurately reconstructed later in the analysis.
The distribution of the baseline for each channel in the detector is determined in a
dedicated data-taking run, where no collisions occur, so that only the fixed baseline
and the superimposed noise can be measured. The average value of the distribution is
used for the baseline subtraction and the deviation is used to set the zero suppression
level.
2.3.3.5 Power Consumption
Both the TPC and MCH are planning to reuse the existing cooling system, power
supplies and power routing that is already in place. The TPC uses a water-cooled
copper envelope on the front-end card to keep the temperature of the detector close
to 21
◦ C. For the TPC the existing cooling can handle up to 35 mW/ch whereas the
power supply and distribution for the MCH is limited to about 13 mW/ch.
2.3.3.6 Slow-Control
Assuming the default start-up configuration of the device is defined with settings that
are close to what the TPC and MCH requires, there would not be a need to do many
configuration changes after the device has cold booted. For this reason, a low-speed
configuration is sufficient. The simplest option is to use I
2 C (Inter-Integrated Circuit)
as it provides multi-drop communication both ways using only two signal, which