[SI-LIST] Re: MPC8630E Freescale Oscillator

Hello Edi,

Interesting spec with a few unanswered questions....
It begins with the 1ns rise/fall times. This is very
much dependent upon the clock input capacitance. The
clock input timing section does not mention the input
capacitance but further in the spec I read 6~8pF for
several inputs so lets assume this number. Most clock
oscillators are spec'd with a 15pF load so what you're
looking for is a spec of 2ns typ., 3ns max. at this
load. This is actually very typical for "standard
drive" (8mA~10mA) LVCMOS outputs. Also note the levels
for the rise and fall times: 0.4V~2.7V. More common is
10%~90% of VDD which is 0.33V~2.97V. Not that much
different so not an immediate issue....
Jitter is always a fun subject. +/-150ps sounds easy
enough. Most clocks claim better than +/-50ps period
jitter. But lets check the notes because the table
does not mention the kind of jitter. "Total
Jitter"....? Total jitter is usually accompanied with
a bit error rate (BER) number, like 1E-12. However,
assuming 1E-12, your average clock will not be in much
trouble yet. Then I read "short term and long term",
bringing up the immediate questions: "how short" (1
period?) and "how long?" (10us?). Here your average
clock may get in trouble on the "long term" side. The
most common clocks these days are programmable PLL
types and they may show some jitter accumulation at
longer periods like 10us. Actually, a decent PLL based
clock should still be able to do the +/-150ps easily
at 10us interval but there are also a number of 'non
decent' type out there....
Note 5 is interesting where they specify the maximum
loop bandwidth of the clock device as if they are
already expecting you to use a PLL. Ironically a PLL
with a higher loop bandwidth will have less long term
jitter so you're looking for a compromise but still a
doable compromise, I think. Your biggest challenge
will be to explain these requirements to a supplier.
;-)  You will probably be best off contacting a
crystal oscillator manufacturer and refer to this
spec.

Regards,
Eddy van Keulen
www.phaselink.com

--- Edi Fraiman <EdiFraiman@xxxxxxxxxxxxx> wrote:

> Hello,
>  
> Does anybody have a recommendation for a 33.33MHz
> oscillator for the
> MPC8630E Freescale PowerQUICC Processor?
>  
> According to the datasheet
>
http://www.freescale.com/files/32bit/doc/data_sheet/MPC8360EEC.pdf
> 
> (Table 8.) Oscillator rise/fall time  should be 1ns.
> 
>  
> 
> Best regards,
> 
>  
> 
> Edi Fraiman
> 
>  
> 
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