1. Michael Lupberger Dorothea Pfeiffer
VMM2 Studies
Michael Lupberger
Dorothea Pfeiffer
RD51 miniweek
This work was funded by the EU Horizon 2020 framework, BrightnESS project

2. Schematic of Setup Pulser Oscilloscope CH1 CH2 PC with Georges VMM DCS
GND
VMM Hybrid
10 kW
VMM2
50 W
Spartan
FPGA
GND
VMM2
50 W
10 kW
VMM 1 Ch 11
VMM 1 digital data
SRS
NIM for
SRS trg
1.7 pF
M0 analog mon

3. VMM2 Logic

4. VMM2 hybrid connections

5. Probe at capacitor connected
Overview
Zoom on falling fast falling edge (negative charge)
Pulser CH2
Voltage before capacitor
M0: VMM analog output
NIM Trigger for SRS

6. Probe at capacitor disconnected
Zoom on falling fast falling edge (negative charge)
Zoom on falling fast falling edge (negative charge)
Pulser CH2
Pulser CH1
M0: VMM analog output
NIM Trigger for SRS

7. Single pulse from pulser CH 1
Voltage before capacitor
NIM Trigger for SRS
M0: VMM analog output
Increasing input charge

8. Pulses from pulser CH1 and CH2
Delay CH1 – CH2: 200 ns
Peaking time 25 ns
Delay CH1 – CH2: 500 ns
Peaking time 50 ns
Delay CH1 – CH2: 200 ns
Peaking time 50 ns
Delay CH1 – CH2: 500 ns
Peaking time 200 ns

9. VMM2 digital output narrow pulses
Question: What is the minimum delay, such that two pulses are resolved by the VMM logic
(in the analog part, as we have seen, they are clearly separated at e.g. 200 ns and 25 ns
peaking time)
-> Answer: (by just looking at the frame size of the SRS packages): ≈500 ns
More quantitatively: events with double pulses - over threshold flag of measured hits
Dt = 600 ns
Dt = 500 ns
Dt = 480 ns
2x60000 pulses seen
≈ 2x60000 pulses seen
But some are not over threshold
(tail caught)
≈ 1x60000 pulses seen

10. VMM2 digital output narrow pulses
Question: What is the minimum delay, such that two pulses are resolved by the VMM logic
(in the analog part, as we have seen, they are clearly separated at e.g. 200 ns and 25 ns
peaking time)
-> Answer: (by just looking at the frame size of the SRS packages): ≈500 ns
More quantitatively: events with double pulses – amplitude of measured hits
Dt = 600 ns
Dt = 500 ns
Dt = 480 ns
2x60000 pulses seen
≈ 2x60000 pulses seen
But some are not over threshold
(tail caught)
≈ 1x60000 pulses seen

11. VMM2 digital output narrow pulses
Question: Can we reconstruct the time difference between the two pulses?
-> Answer: Yes we can!
Dt = 600 ns
Dt = 500 ns
≈ 2x60000 pulses seen
But some are not over threshold
(tail caught)
2x60000 pulses seen

12. VMM2 digital output Summary narrow pulses
BC clock 40 MHz
TAC slope 125 ns
Gain 1 mV/fc
Pulse frequency 1 kHz
Shaping time 25 ns
Time of threshold crossing
For a time delay >= 600 ns, both pulses are recorded with the correct ADC and delay
For delays between 600 ns and 480 ns, the second pulse is detected less often, with a lower
ADC, and the reconstructed time delay is too small
For delays < 480 ns the second pulse is lost

13. VMM2 digital output Wide pulses, comparison APV25
Digitized full waveform
ADC
Time bin [25 ns]

14. VMM2 digital output Wide overlapping pulses
VMM2 detects first peak with correct ADC and time
VMM2 detects second peak only when threshold is very high, incorrect ADC (peak minus trough)
ADC
Time bin [25 ns]

15. VMM2 digital output Summary wide overlapping pulses
BC clock 40 MHz
TAC slope 125 ns
Gain 1 mV/fc
Pulse frequency 1 kHz
Shaping time 25 ns or 200 ns (overlapping)
Time of threshold crossing or peak time
The second peak of overlapping pulse is still partially resolved with a time delay of 600 ns, but only if the discriminator threshold is high