11 Dec
2003
11 Dec
'03
8:10 a.m.
I wrote:
> Without decoding the data, it is proposed to
sample the data at 50 Mbps
> or more.
Andy wrote:
Why so fast? You only need sample at 2x the bandwidth.
2x is the theoretical minimum; sampling at 2x isn't always adequate
in practice due to various real-world limitations.
The minimum write data pulse width spec for the WD1000 controller
is 60 ns. If we were sampling and reconstructing a sine wave with
a 120 ns period, 16.7 MHz sampling would be adequate. But that
wouldn't yield good results for square waves, and there wouldn't be
any margins. In practice, I suspect that 33.3 MHz sampling would be
barely adequate provided that no other problems arise. Operating at
50 MHz seems advisable to have reasonable margins.