[time-nuts] femtosecond jitter anyone?
Chris Mack / N1SKY
sometimesyoufeellikeanut at twentylogten.com
Wed Apr 8 23:32:20 UTC 2009
>> This is a good idea for testing..
> Applying jitter frequencies for jitter tolerance testing is standard
> stuff and needs to be done. Jitter tolerance curves match up with MTIE
> tolerance curves very neatly.
Of course, here is the weird part... It's not SONET; but it is a chip
that can be used for SONET... This is for a very specific form of
audio clocking (not audiophile, nor consumer) for a mastering
engineering application. Common input clock frequencies: 44.1kHz to
96kHz or also a 10MHz rubidium.
The DSP PLL is this chip (I am still learning the intricacies of this
The system clock (to drive the DSP and the DSP's DCO) is essentially
a jitter reference, pins XA and XB (differential, single ended
capable); Jitter is transferred nearly 1:1 from XA,XB to CLK_OUT.
This is the 38.88 MHz reference from Vectron with some skirting
issues to be filtered before connected to the XA and XB pins.
The input (on CLK_IN pins) is the source clock to be cleaned (e.g.,
44.1kHz to 96kHz or 10MHz Rb).
The output (on CLK_OUT pins) is 11 MHz to 25MHz for 256x
oversampling master clock for ADCs and DACs
24-bit accuracy for 40kHz (88.2kHz to 96kHz sample rate encompassing
a 45/55 anti-alias filter) shows the need for sub picosecond timing
Of course 24-bit in the real world is hard to achieve (even the new
"32-bit" converters have a problem with it) with issues internal to
the sampling mechanisms in a DAC / ADC, but with some out-of-band
dither and thermal management, coupled with low jitter sampling
clock, there may be an additional bit or so to be obtained. This is
all part of the experiment....
>> I have Howard Johnson's book for
>> I think a normal LC tank would be more suitable for that task.
> It's a good introductional level book for digital signals, but isn't
> very applicable to waveshaping or clock characterisation and testing
Yes, HJ's books leaves me wanting a little more... seems like an
analogue / RF book for digital folks.
I am looking for sharp Q to get rid of any skirt around the 38,88MHz
of the Vectron OCXO.
Temperature can be obtained from cooling componentry already in situ,
such that a known temperature is established.
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