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On Jun 2, 2008, at 3:20 PM, Matt Ettus wrote:
The RFX400s have PLL chips on them. The PLL chips on the 2 boards
are fed the same reference clock since it comes from the
motherboard. However, they both divide the clock down by the "R
Divider" value, which is typically 8. The RFX400 has a second
divide-by-2 as well for a total of 16. Thus there would be an 8-way
ambiguity, since the dividers could be at different phases. Thus
the relative phases between 2 boards can only be one of 16 discrete
values. This value will stay constant as long as you don't retune
to a different frequency or allow the pll enable pin to go low.
If you set your RF frequency to a multiple of 64 MHz, however, there
will be no ambiguity.
What of the above is {the same, different} for the RFX2400's?
I'm using Rev 4.2 USRPs with RFX2400 Rev 30s. Presumably with Rev 4
USRPs but older RFX2400s with 64 MHz oscillators I could make the mods
necessary to use the FPGA refclk.
- -Dan
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