D100 Circuit Overview - Pyramid D100 User Manual

PSI System Controls and Diagnostics

10.2 D100 Circuit Overview

y
39pF
499R
x
Figure 12. D100 block schematic.
The amplifier stage is a fast current to voltage converter with 499 ohm feedback. The circuit
allows optional series input resistance at x and different feedback at y in order to adapt to
different input signal characteristics. The values shown are those for readout of sodium iodide
scintillators. A 50 ohm high speed differential amplifier then provides voltage gain and
conditions to the signal for the ADC input. The gain of this stage is given by 0.01*R
nominal value of R is 316 ohm. ADC conversions are streamed to the FPGA which executes
F
the pulse processing algorithms in the digital domain. There are auxiliary outputs for the high
voltage program (0 to +2.048 V), the gate control (5V differential) and a test pulser LED (5 V
through 2 kohm). There is an input for a remote AD596 temperature sensor.
The input stages do provide a small amount of integration of the signal, in order to improve
signal to noise ratio and ensure stability. However the basic shape of the sodium iodide
scintillator / photomultiplier output is preserved so that it can be used by the discrimination
algorithms. Figure 13 shows a circuit simulation result which illustrates this behavior.
D100 User Manual
39pF
R
F
50R
50R
50R
50R
R
F
39pF
D100_UM_081027
DC-DC
converters
ADC
39pF
80 MHz FPGA
14 bit
LEDs DAC
Microcontroller
+24 V in
Communication
loop
Data stream out
PMT HV program
PMT gate
Test pulser LED
Temperature sense
. The
F
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