Design and Development of a Diagnostics Client for a Beam Loss ...

Design and Development of a Diagnostics Client for a Beam Loss Measurement System at CERN
verter is attached to the differential output of the integrator.
• Direct Analogue Digital Conversion (DADC) circuit. In this method the ADC converter
is attached to the input resistor on which the voltage drop is measured.
In this way the measurement range is split into two overlapping ranges. The FDFC is
used between 10 pA – 30 mA and the DADC between 100μΑ – 200 mA. The analogue
switch, that selects which of the two circuits is active at any given time, is automatic and
controlled by the FPGA device. A module inside the FPGA is monitoring the data stream
and depending on the measurements it receives, selects the most suitable measurement
method for the next period. This switching between the two principles, depending on the
input current, can be seen in Figure 5.
Figure 5: FDFC and DADC switch
The FDFC method is using an integrator and a status signal to select in which branch of
the fully differential stage, the input current is integrated. This mechanism is shown in
Figure 6.
The FDFC circuit’s output is processed by the FPGA device. The outputs of both ana-
logue comparators are complemented by the ADC samples to reach higher measurement
precision. The calculation of the integrated loss is triggered by the FPGA over a 2 μs
period. [18] This also marks the integration period, in which the measurement result is
produced. In general, most of the operations are handled by the FPGA. So, the FPGA
defines when the acquisition period starts or stops. It also keeps a count of the pulses
occurred in the acquisition period and clocks the ADC circuitries in order to make differ-
ences of the recorded ADC values. Finally, it processes the data and provides this 2μs
integral per acquisition channel.
Emmanouil I. Angelogiannopoulos 20