Specifications

System Parameters of the DPC-230 47
Both TDC chips can be switched on and off by the ‘active’ button. If one of the TDCs is not
used it should be switched off to avoid unnecessary software actions.
For both TDCs the inputs can be switched to ‘LVTTL’ or ‘CFD’. Each TDC either has 8
LVTTL inputs or 2 CFD inputs. The LVTTL configuration is shown in Fig. 77, left, the CFD
configuration right. It is possible to combine LVTTL operation in one TDC with CFD opera-
tion in the other.
Fig. 77: Input configuration panel
All inputs can be individually switched on and off by the ‘active’ buttons. Moreover, the func-
tion of the inputs can be defined. The function can either be an input for a detector signal, a
reference input from a light source, or a marker input. For TCSPC operation channel 12
(CFD 4) is always the reference.
‘Edge’ defines the active edge of the input signal. The active edge of the CFD inputs is always
the falling edge; for the LVTTL inputs either the rising or the falling edge may be used.
Please note: For SPAD modules with TTL outputs ‘rising edge’ must be selected.
CFD and SYNC Parameters
The CFD parameters define the thresholds and the zero-cross levels of the CFD inputs. The
thresholds can be set from 0 to -510 mV, the zero-cross levels from -96 to +96 mV. CFD
thresholds smaller than -20 mV can result in noise pickup and should therefore be avoided. If
a detector requires a threshold this low a preamplifier of sufficient gain should be used.
Fig. 78: CFD threshold and zero cross settings.
Please note that in the TCSPC mode CFD 4 is used for the reference input.
SYNC Frequency Divider
In the TCSPC mode the fourth CFD channel is used as a reference input. To display either 1,
2, or 4 signal periods of the recorded signal (see Fig. 6, page 4) the fourth CFD channel has a
selectable frequency divider. The divider ratio is selected under ‘SYNC parameters’. The pa-
rameter is available only in the TCSPC mode.