PDM-IR user manual v
3.0.3
Micro Photon Devices S.r.l. – Italy All Rights Reserved
13
4
PDM-IR Specifications
The PDM-IR module is a complete system for photon counting in the NIR range (Figure 1, Figure 2) and it can
be used either in gated or in free-running mode. Both modes of operations can be optimized through the use
of several user selectable parameters, all controllable from a computer using either the delivered SDK library
or the provided Windows® PC software.
When used in gated mode (see Figure 3 and paragraph 2 for details), the TRIGGER GATE signal, for GATE
frequency generation, can be provided either using an INTERNAL TRIGGER or through an external signal fed
into the TRIGGER IN input. In the former case, for synchronizing the GATE with other instruments, it is
possible to replicate the INTERNAL TRIGGER at one of the two available outputs, depending on the desired
pulse polarity, i.e. the TTL AUX OUT or the NIM AUX OUT. Complex external trigger patterns can be also fed
to the TRIGGER IN input, since it accepts not only periodic but also aperiodic signals as shown in Figure 12.
Additionally, it is possible to create even more complex TRIGGER GATE patterns for GATE generation, by
combining the auxiliary input AUX IN signal with the INTERNAL TRIGGER or the TRIGGER IN, and by using the
provided user-selectable logic functions (see paragraph 4.1 for more details). An example of such
combination is shown in Figure 10. Finally, GATE signal can be generated either by exactly replicating
TRIGGER GATE (Figure 13) or by creating a new signal, synchronized with the rising edge of TRIGGER GATE
and with a fixed gated-ON width equal to the user set T
ON
value (Figure 12). See paragraph 4.2 for more
details. Of course, as discussed in paragraph 2, independently of the chosen trigger pattern, GATE signal is
disabled for the duration of the HOLD OFF time, following each avalanche triggering. At the end of the Hold
off time, two types of reset are possible depending on how the gate electronics handles what happens when
the hold-off terminates inside a gate-ON time window. See paragraph 4.2 for a detailed description.
When used in free running mode (see also Figure 4 and paragraph 2), the INTERNAL TRIGGER, TRIGGER IN
and AUX IN signals are meaningless and the SPAD is always on until a SPAD avalanche is initiated. In this case,
the avalanche current is first quenched and then, after a well-defined hold-off, the detector is immediately
enabled (see paragraph 4.2.3). Of course, in free running mode only one type of hold off reset is possible
since GATE signal is always immediately enabled at the end of the hold-off time, as shown in Figure 14.
Concerning the SPAD parameters Hold-OFF time, excess bias voltage and SPAD temperature, they are all user
selectable to get the best results from the measurement (see paragraph 4.3 for in-depth description).
Concerning the outputs: PHOTON OUT is the low timing jitter output signal, precisely marking the photon
detection time; NIM AUX OUT and TTL AUX OUT, shouldn’t be used for low jitter timing measurements and
