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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%. |
| | |
| | Bruce |
| | |
| |
