Hi Weiwei You'll need a few things:* a PPS (pulse per second) signal, which can be derived from something like a GPS receiver. * a PPS splitter box, so that you can split the PPS into four signals. You then need four coax cables of the same length to connect these to your ADC boards. For example: https://casper.berkeley.edu/wiki/16_way_1PPS_driver * a stable frequency synthesizer. For more stability you can often lock these to an external frequency standard, like a 10 MHz reference tone. A good GPS unit might also be able to supply this. A Valon 5007 will be fine for this (lots of CASPER people are using this or similar). * A RF splitter, to split the clock, and of course four coax cables of the same length to connect to your ADCs.
I've attached a quick diagram to show what I mean. The important part is that you use the same synth and same PPS for all boards.
A closing note: If you're working at a 5GSPS sample rate, then you should try and make sure that your cables introduce much less than 1/5G = 0.2ns delay difference between them. This is about 6cm, so a set of coax specified to +/- 1cm should be okay.
Cheers Danny
<<attachment: sync-pps.png>>
