Cornelius DPC 230 Especificaciones descargar pdf (Pagina 23)

Operating the DPC-230

LVTTL Inputs

The LVTTL inputs of the DPC-230 are designed to receive single-photon pulses from SPAD

(single-photon avalanche photodiode) modules. LVTTL means ‘low voltage TTL’, i.e. the

inputs are triggered by signals as low as +1.5 V. The pulse duration can be as short as 2 ns.

The location of the LVTTL inputs at the DPC board are shown in Fig. 20. The signals are fed

trough the back panel of the computer via cable adapters (Fig. 20, middle and right).

Fig. 20: Location of the LVTTL inputs at the DPC board (left), cable adapter (middle), DPC and adapters in-

serted in computer back panel (right)

Due to the limited size of the computer back panel MCX connectors had to be used for the

LVTTL inputs. Please contact bh if you need additional cables with MCX connectors.

The LVTTL inputs are overload-protected and accept input voltages up to +5V. The input

equivalent circuit is shown in Fig. 21.

100 Ohm

to internal

circuitry

51 Ohm

Termination

board

Input

Fig. 21: Equivalent circuit of the LVTTL inputs

The LVTTL inputs of the DPC-230 board are terminated with 50 Ω via a termination board.

The board is plugged into a connector close to the LVTTL inputs at the DPC board, see Fig.

20, left. We recommend to use the termination whenever the signal source is able to drive a

50 Ω load. For signals from standard TTL and LVTTL logics it may be necessary to remove

the termination. Operation without termination can cause reflections on the signal lines and

thus lead to double triggering. However, for standard TTL or LVTTL sources reflections are

damped by the source impedance and are thus rarely troublesome.

Connecting SPAD and PMT Modules to the LVTTL Inputs

The LVTTL inputs can be used for all commonly used SPAD modules and a number of PMT

modules with internal discriminators and TTL outputs. Some frequently used detectors are

listed in the table below.

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 69 70

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Cornelius DPC 230 Especificaciones Pagina 23