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Choosing clock source for use on PCB


Advanced Member level 2
Apr 17, 2011
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I am creating my first FPGA PCB. It needs clock source.

When I went to Mouser website looking for it, it gave me this list of options contained in the image_1 attached.

When I went to RS website looking for it, it gave me list of options contained in the image_2 attached.

I am basically completely confused by this plethora of options. I just need a single frequency clock source. The frequency range is 10MHz to 100MHz. This is because I might choose a few different components for this PCB. The PCB is being created for purpose of learning PCB design.

What component am I supposed to look for?


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If the circuit is digital then a CMOS output "clock in a can"
is my choice. Wide variety of fixed frequencies in the
1-100MHz range.

To go higher you are probably looking at a complex lashup
of reference oscillator, PLL and VCO (w/ filters) to gen and
lock a higher frequency clock by divider feedback (most PLLs
have on-chip counters, but beware the need for even more
"hand holding" if there's registers that need stuffed, etc. -
we had some customers who really liked the simpler,
broadside divider-code pins for lightweight systems).

This latter would also apply to any RF system, where you
must create an accurate reference frequency if you want
channel selectivity and so on. A clean LF clock and a VCO
tuned by a PLL.

Now within just the logic clock ranks, you can find a lot of
variation particularly in tolerances. That's probably the main
thing to know, "how good does it have to be?". Because you
could also make a crude sloppy clock with a hex inverter and
a R and C. If you like crude, sloppy and already there in the
parts bin.

Honestly, to me it seems you try to find a solution for an unknown problem.
This is like going backwards.

Thus my recommendation: First determine the clock's requirements:
* The FPGA (datasheet) tells you the possible frequency range, but also voltage levels, waveform, maybe even jitter and other specifications
* and your application tells what system clock frequency (maybe range) it needs. Maybe your application even needs several different frequencies. And accuracy of frequency...and so on.

Then - after you have your requirements - you can go for a part search.

Actually I am creating a PCB for the sake of it i.e learn PCB design. So, there are no actual requirements other than that I must make it as much efficient learning experience as possible.

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