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# Functional system specifications
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# Functional system specifications
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- To be filled in the coming days.
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- 5 inputs, TTL with 50 Ohm termination.
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- Time tags apply to rising edges of inputs.
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- 1 ns resolution or better.
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- Accuracy (of time-tag differences between channels): */- (500 ps*
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timebase accuracy).
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- Timebase accuracy: +/- 4ppm.
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- Implementation details: timebase from a local TCXO on FMC card
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and needs calibration. The 4ppm accuracy will only be reached
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when used on a White Rabbit enabled FMC carrier.
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- External inputs need to be protected against +15V pulses with a
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pulse width of at least 10us @ 50Hz (with protection diodes if
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possible).
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- SMC connectors for all inputs.
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- Minimum input pulse width: 100 ns. Pulses shorter than 20ns should
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be ignored.
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- A circular buffer will contain time tags for at least the last 100
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input pulses. These time tags will at first be rough UTC (counter
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initialized by SW) giving ~ms accuracy. Later, with a WR-enabled
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solution, they can be much more accurate. Differences between
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channels will not suffer from this accuracy problem because the
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offset with respect to UTC will cancel.
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