All,
One thing to keep in mind -
Any clock divider chain that reduces by a non-power-of-two will introduce
time jitter (time noise) into the output. While the effects may be small,
it can affect precision of frequency measurements.
Bart
Jouko Ritakari wrote:
> Hi Randy,
>
> We have just sampled at higher frequency and discarded extra samples.
> I think sampling frequency was 512 MHz and output frequency 32 MHz.
>
> In our case clock was generated by a Maxim or Analog Devices PLL clock
> generator evaluation kit which costs about 100 dollars.
>
> It is a good idea to have a low-pass filter in the ADC input, saw some
> indication that higher-frequency noise got through.
>
> Cheers,
> Jouko
>
> "Life is pretty simple: You do some stuff. Most fails. Some works. You do
> more of what works. If it works big, others quickly copy it. Then you do
> something else. The trick is to do something else."
>
> On Fri, 24 Oct 2008, Randy McCullough wrote:
>
> > All,
> >
> > We're dealing with a design which uses an iBOB and an iADC as
> > a front end "sampler" which operates typically with an 800MHz
> > sample clk (interleaved), derives it's logic clock from the ADC at
> > 200MHz and concatenates and streams the low-order samples
> > through XAUI port 0 and the high-order samples through XAUI
> > port 1.
> >
> > We'd like to try simply cranking the sample clk down; thereby
> > effectively altering our sampled BW (i.e., 800MHz, 400MHz,
> > 200MHz, 100MHz, etc...). Since our logic clk is always 1/4
> > of our sample clk, and the XAUI ports derive their internal clks
> > from the logic clk, what is the lowest practical speed at which
> > we can run things without wrecking the XAUI ports' operation.
> >
> > Or, put another way, what is the lowest logic clock rate we
> > can use on an iBOB and still maintain reliable XAUI trans-
> > missions?
> >
> > Lastly, are there any other aspects of an iBOB/iADC design
> > which might place a lower constraint on our speed --such as
> > the ADC chip, LWIP, etc., etc., etc.?
> >
> > Thanks,
> >
> > Randy
> >
> >
> >
