[time-nuts] low noise multiplication to 100 MHz
jimlux at earthlink.net
Fri Jan 22 21:40:15 UTC 2016
On 1/22/16 12:43 PM, Artek Manuals wrote:
> OK ...coming back to the original post and see if we can nail down ALL
> the design requirements
well, I wasn't really thinking in terms of formal design requirements..
(I get more than enough of that at work<grin>)
I was more looking for potential circuits..
But, since you ask...
> You said
> "My tiny 100 MHz low noise OCXOs are unexpectedly delayed at the mfr, and
> I'm looking at alternative schemes.
> One is to get 10 or 20 MHz OCXOs (typically in stock) and multiply them
> up. I've got the Wenzel ap notes on 2diode and using HCMOS (and I've
> used the packaged Wenzel multipliers), and I think I have some spare
> board real estate on another board."
> So I ask then, what is the real set of design requirements
> 1) Space of a few sq CM is the goal
> 2) 5X or 10X frequency multiplication
> 3) Input and output level (?????????)
the oscillator is a HCMOS output, so figure swinging about 3.5V
Output.. I'm feeding differential clock inputs on ADCs. I'll bet a +/-
300mV swing would work.
> 4)Title said "Low Noise" needs better definition as to what kind of
> noise and how far down. Are we to be concerned about harmonic and spur
> content as compared to real random white noise?
This is time-nuts.. it has to be perfect..
But realistically, my source is probably going to be about -90dBc/Hz at
1 Hz, -125 at 10Hz, -145 at 100 Hz. I'm going up by a factor of 10, so
I'd expect 20 dB worse plus a little..(nothing is perfect, eh?)
Call it maybe -100 to -95 at 10 Hz, -125 to -120 at 100 Hz and so forth.
harmonics are interesting: it's the sample clock into an ADC. So
harmonics of the 100 aren't a big deal. harmonics of the 10 or 20 are.
If you have significant 90 or 110 contaminating the 100, then you get
weird spurs.. (I had this problem on a software radio where the 50 MHz
sample clock was contaminated with some 66 MHz from the CPU)
Spurs cause the same issues.
ON the other hand... spurs that are pretty low don't make much
difference if you're digitizing a signal that is close to the noise
floor: the spur multiplied by the desired signal is usually lower and
down in the noise. Strong CW in band signals, though, are a real pain.
> 5) Power requirements (0 to 5V at ?? ma ...or?)
Very low is nice..
the base oscillator is a few hundred mW. I'd say something like a watt
all told would be acceptable.. But on the other hand, when you get up
to "watts" and "big" then you might as well just buy another OCXO that
is at 100 MHz instead of the nifty little tiny ones I was planning to
use. (of course, the big OCXOs tend to have +12V power, which I don't
have..I have unregulated 7.5 to 8V and regulated 5 or 3.3.
It's an interesting tradeoff.
> 6) Stability requirement in PPM?
That's driven by the base oscillator. But in reality, I don't have a
particularly tight long term frequency requirement. I have a long term
frequency knowledge requirement (which can be met by just counting the
oscillator with the GPS 1pps).
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