Gearslutz.com - View Single Post - Recipe: how to cook a best in class 2-ch pre-amp with a/d convertor?

Francis Vaughan · 12th February 2008, 07:17 AM

Moving a wordclock around is fraught with all sorts of problems. You are working in the RF domain, and the issues with impedance matching, transmission lines, reflections and terminations are really awful. Lots of care is needed. It is easy to get something that works, but even easier to get something that has very difficult to diagnose and sort out sonic problems. To manage 16 bit accuracy you need to keep the phase noise under .3ns, and for 20 bit, 10's of picoseconds.

The best and easiest way to do this is to keep all the ADC chips on one board, and use stripline construction to distribute the clock. A 6 layer board is pretty much mandatory. If you use coaxial connections and a distribution amp typically a time domain reflectometer is needed to ensure a good distribution.

It may be that the eval board's design, where it doesn't take a word clock, but takes and external crystal frequency clock may be slightly easier to cope with, but in reality the same care is needed.

12th February 2008, 07:17 AM	#7
Francis Vaughan Lives for gear Join Date: Jan 2008 Posts: 538	Moving a wordclock around is fraught with all sorts of problems. You are working in the RF domain, and the issues with impedance matching, transmission lines, reflections and terminations are really awful. Lots of care is needed. It is easy to get something that works, but even easier to get something that has very difficult to diagnose and sort out sonic problems. To manage 16 bit accuracy you need to keep the phase noise under .3ns, and for 20 bit, 10's of picoseconds. The best and easiest way to do this is to keep all the ADC chips on one board, and use stripline construction to distribute the clock. A 6 layer board is pretty much mandatory. If you use coaxial connections and a distribution amp typically a time domain reflectometer is needed to ensure a good distribution. It may be that the eval board's design, where it doesn't take a word clock, but takes and external crystal frequency clock may be slightly easier to cope with, but in reality the same care is needed. __________________ The night is coming, and its filled with dark surprise.