Teledyne LeCroy QPHY-USB - Manual (Page 44)

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QPHY-USB Operator’s Manual Rev F
8. Now load the “IN_ADD1” waveform into the generator (see Appendix A for details). The generator
amplitude should be set to the 400 mV. This generates IN tokens with a full 32 bit sync and nominal
amplitude.
9. Verify that there is a response packet (NAK) for all packets sent from the data generator, as in step 7.
10. Reduce the amplitude of the data generator packets in small steps while monitoring the response from the
device on the oscilloscope. The adjustment should be made to both generator outputs such that the level
is set to the same value for both outputs. Reduce the amplitude until the NAK response packet begins to
become intermittent, as shown in the figure below. At this point, increase the amplitude such that the NAK
packet is not intermittent. This is just above the minimum receiver sensitivity levels before squelch.
Figure 48. Intermittent Response to IN tokens at low amplitude
11. Measure the zero-to-positive peak of the packet from the data generator using the cursors in the lower
(zoom) window of the oscilloscope display. Use the upper cursor position knob to position cursor 1 on the
zero level of the waveform and the lower cursor control knob to position cursor 2 on the positive peak of
the waveform. The cursor should be positioned on the plateaus of the wider pulses to avoid inflating the
reading due to overshoots. The difference voltage is indicated in the F1 waveform box, “zoom(C1)”, at the
lower left corner of the oscilloscope screen. Record this value as EL_17 positive threshold.
12. Move cursor 2 to the negative peak of the waveform in the lower window of the oscilloscope screen, using
the lower cursor control knob again, and position the cursor on the wider plateaus to avoid overshoots.
Read the difference voltage in the waveform information box at the bottom left of the oscilloscope display.
Record this value as EL_17 negative threshold. The receiver must continue to NAK packets above +/-
150 mV to pass EL_17.