[time-nuts] Low noise frequency multiplication

[Stephan Sandenbergh]

Darn, the table is a mess. Here is the corrected one:

LVPECL Outputs	
Hz	dBc/Hz
1	?
10	-127
100	-145
1k	-153
10k	-158
100k	-158
1M  	-158

10MHz OCXO	
Hz	dBc/Hz
1	-100
10	-130
100	-152
1k	-160
10k	-165
100k	-165
1M  	-165

10x Multiplied	
Hz	dBc/Hz
1	-80
10	-110
100	-132
1k	-140
10k	-145
100k	-145
1M  	-145

Diverence 	between 10MHz x10 Multiplied and AD9512
Hz	dBc/Hz
1	17
10	13
100	13
1k	13
10k	13
100k	13
1M  	13


Regards,

Stephan.


On 3/1/07, SAIDJACK at aol.com <SAIDJACK at aol.com> wrote:
>
> In a message dated 3/1/2007 05:50:30 Pacific Standard Time,
> stephan at rrsg.ee.uct.ac.za writes:
>
> Hi  Said,
>
> It seems there are indeed many ways to kill a cat. What happens  to the
> close-in phase noise using this method?
>
> Cheers,
>
> Stephan.
>
>
>
> Hi Stephan,
>
> you are asking the right questions :)
>
> The near-carrier phase noise depends on the 1GHz reference  source:
>
>   1) If it is a crystal such as the Xpresso 1GHz series from  Fox, then the
> phase noise of the 1GHz reference will actually be reduced by 20dB  for every
> 1:10 reduction in output frequency!
>
>   2) If you are using a standard (noisy) VCO, then the phase  noise of your
> 10MHz reference source will be increased (multiplied) by the  standard 20dB
> for every 10x increase in output frequency.
>
> This is due to the fact that when using a VCO, the PLL will use  the
> reference crystal to actually reduce the phase noise of the VCO. You will  likely use
> a loop filter with 1 - 15KHz BW. So you get the 10MHz  reference noise
> multiplication inside this loop filter BW. Outside the BW,  it's the DACs and VCO's
> noise floor.
>
> But for a crystal 1GHz reference, you would use a simple PLL with an
> extremely small loop filter BW (say <1Hz) so that your total phase noise is  only
> dependent on the 1GHz crystal reference, and not at all on your 10MHz  reference
> anymore. The PLL could be as simple as an Exor gate in this  case.
>
> I have been trying to get phase noise/jitter specs from Fox for their  new
> 1GHz Xpresso crystals, but it is hard to come by. I am waiting for  feedback
> from them. They only specify "UI"!?
>
> But let's say these are as good as advertised, and for me that would mean
> say better than -95dBc/Hz at 10Hz offset from 1GHz carrier, then by reduction
> through the DDS, we would theoretically get -20dB below this, or -115dBc/Hz at
> 100MHz output.
>
> I would assume that at that point the noise floor of the DDS DAC chip is  the
> limiting factor at <-150dBc/Hz as it is for the well-known AD9858 chip  (it
> actually measures about -155dBc/Hz).
>
> AD has new chips coming this month, see for example the AD9957 with a 14  bit
> DAC (9858 has 10 bits), I assume these will have an even lower phase noise
> floor and very important lower spurs than the AD9858, the datasheet  says TBD:
>
> _http://www.analog.com/UploadedFiles/Data_Sheets/AD9957.pdf_
> (http://www.analog.com/UploadedFiles/Data_Sheets/AD9957.pdf)
>
> Bye,
> Said
>
>
>
>
>
>
>
>
>
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