Fine Delay Functional Specifications¶

Hardware¶

• 1 TTL trigger input, selectable between front panel and FMC connector. Front panel input has programmable 50 ohm termination, the default power-up state is high impedance. A LED will signal termination status. This input is shared by all output channels.
  - External input protected against +15V pulses with a pulse width of at least 10us @ 50Hz.
  - Rising-edge sensitive
• 4 TTL outputs capable of driving a 50 Ohm load.
  - 2 V/ns or faster rising edges
  - Output levels: TTL Voh 3.6V with 50 Ohm load, 5.0 V with Hi-Z load
  - Default power-up state: low, with no glitches.
  - Must withstand a continuous short-circuit on all the outputs at the same time.
• LEMO 00 connectors for input and outputs.
• FMC Low pin count (LPC) connector, 2.5/3.3 V Vadj required.

Modes of operation¶

• Pulse delay: a pulse coming to the input triggers generation of a pulse or series of pulses of given width and repetition rate on chosen outputs after a certain time programmed by the user (see fig. 1a).
• Single channel TDC: time tags of incoming pulses are provided to the user via a circular buffer.
• Pulse generator: produce a pulse or a series of pulses of arbitrary length and repetition rate starting at a given UTC/TAI time (see fig. 1b).

Notes:

• TDC mode can be used in parallel with Pulse Delay/Pulse Generator mode.
• Pulse Delay/Pulse Generator modes can be used simultaneously on different outputs. Mode of each output is controlled individually.

Performance and limitations¶

Common parameters (all modes)¶

• Minimum input pulse width: 100 ns. Pulses below 24 ns are ignored.
• Maximum input pulse rate: 1 MHz (minimum pulse spacing: 1 us).
• Minimum time between the end of the last output pulse and the next trigger pulse: 200 ns
• Output pulse width: 50 ns - 1 s (10 ps resolution).
• Output pulse spacing: 100 ns - 1 s (10 ps resolution).
• Output pulse repeat count (train generation): 1 - 65536 pulses or infinity (continuous mode)
• Timebase accuracy: ± 4ppm. Timebase from a local TCXO on FMC card needs calibration. The 4ppm accuracy is the one of the on-board TCXO. Cesium-quality accuracy will be reached when used on a White Rabbit enabled FMC carrier.

TDC¶

• Resolution: 28 ps
• Precision (std. dev): 55 ps
• Accuracy: ± (300 ps + timebase accuracy)
• 1024-entries circular buffer with time tags for input/output pulses.
• Buffer interrupt (with timeout/threshold coalescing)

Fig 1. Illustration of Delay/Pulse Generator mode operation.