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precision_timing:minimizing_noise_bandwidth [2013/01/08 19:00] (current)
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 +====== Minimizing Noise Bandwidth in Closed Loop Systems ======
 +Subject: GPSDO time constant
 +>> ​    
 +>>>​ Magnus Danielson <​magnus@rubidium.dyndns.org>​ wrote:
 +>>>​ For ThunderBolt owners it is pretty straightforward to separately adjust ​
 +>>>​ the Time Constant and damping, which is very nice. Use this opportunity!
 +>>> ​      
 +>> Richard Moore wrote:
 +>> So, Magnus (and Tom), what damping factor do you suggest for a TBolt?  ​
 +>> I'm running a verrry long TC now. If 1.2 is not actually critically ​
 +>> damped, what value would be? Any guesses? BTW, I really like that 
 +>> plot of Tom's that tracks the oven and then gets better from the GPS...
 +>> ​    
 +> Magnus Danielson wrote:
 +> Dick,
 +> Assuming that damping factors match classical analysis of damping, then 
 +> the square root of 2 is the answer... 1.414 or there about.
 +> I would be more conservative than that. I would consider damping factors ​
 +> such as 3-4 or so. I have no support from measurements on GPSDOs but it 
 +> is reasonable that the rise of gain at and near the PLL frequency we see 
 +> for other systems will occur and result in similar effects even here.
 +> This gain raises the noise floor and amount of gain is directly coupled ​
 +> to the damping factor. It's just standard PLL stuff all over again. The 
 +> only difference is that we view the result in ADEV or MDEV views.
 +> Cheers,
 +> Magnus
 +Hej Magnus
 +For a second order loop, the noise bandwidth is minimised for a fixed
 +time constant by choosing a damping factor of 0.5.
 +Using a damping factor of 1.414 increases the noise bandwidth by about 60%.
 +Using a damping factor of 0.7071 only increases the loop noise bandwidth
 +by about 6%.
 +A damping factor of 0.3 increases the noise bandwidth by about 13%.
precision_timing/minimizing_noise_bandwidth.txt ยท Last modified: 2013/01/08 19:00 (external edit)
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