Synchronizing Software Defined Radio (and other) clocks on White Rabbit on generic FPGA boards

About

White rabbit is most often used to distribute the traditional 10 MHz and 1-PPS, possible for synchronizing instruments accepting such signals as input. However, many components such as RF frontends need to operate at others clock frequencies and lack the ability to synchronize on a PPS: while being syntonized, their use of dividing PLLs introduces nondeterministic phase and hence time offsets.

In this presentation, we show how nearly any feedback clock can be synchronized on White Rabbit with an implementation of the locksweep on auxiliary soft-plls as initially introduced by Nikhef on the main PLL [1]. We demonstrate this technique by synchronizing the ADCs of AD9361 RF frontends on an Enjoy Digital M2SDR board using the LiteX wrapper at various sampling frequencies.

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