PPS_OUT wrongly reclocked when BE_REFCLK is used as 125 MHz refclk (using HPSEC)
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- Author Maintainer
When BE_REFCLK is used as reference clock on the other Z035 GTX refclk input then CLK_125M_O, used for re-clocking PPS_OUT) is still clocked with the 125 MHz that comes from the LCT6950 PLL. So in this case re-clocking is not in phase with the chosen reference clock.
Work around: When using BE_REFLCK then use the BullsEye SPARE outputs for PPS_OUT to avoid re-clocking. Re-clocking is also one on the HPSEC board.
Next version SPEC7, consider a selection on the VCO+/- input of the LTC6950 that selects either the VCXO or the external BE_REFCLK. When doing so there is no longer a need for a separate GTX input (thus also avoiding the need to use a Z035).
- Author Maintainer
It is decided to omit this suggestion.
Motivation:
- Adding a multiplexer would involve quite a layout effort in the over populated oscillator area.
- The suggested work around (i.e. using BullsEye SPARE outputs for PPS_OUT and re-clock external) can, and should be done with the (clean) external local reference oscillator which must not be "polluted" with the additional LTC6950 phase noise.
- Z035 has to be used anyway due to issue #22
- Peter Jansweijer closed
closed