Hi Erik,
On 2022-02-26 17:36, Erik Kaashoek wrote:
Magnus, Bob,
Thanks for the replies.
@Magnus, I need to study your input a bit longer. What I currently
fail to understand is : Should there be a low pass filter with a 1/100
s corner frequency in series with the Vtune when the ADEV of the
VC-TCXO and the PPS intersect at 100 s? Why not have a Kp of 0.01
instead of an additional low pass filter? I understand how the low
pass filter can help reduce noise from the DAC if needed or is there
another reason?
The reason I did so was that the modulation, which always occurs as you
step back and forth to interpolate, was intentionally moved to as high
frequency as possible to make it as easy to filter out variations from
as possible. This way the filter to remove most of that noise can have a
bandwidth higher than the loop bandwidth, which is needed for loop
stability. When they come near each other, this third pole may create
unwanted pole-splitting moving a pole-pair into the forbiden/unstable
region (right-hand side of Laplace domain or outside the unity circle of
the z-transform-domain).
Hope it makes sense.
Cheers,
Magnus
@Bob, the reason for not converging may be some infrequent
disturbances of the control loop caused by something not yet
identified. Need to do some investigation into the cause.
Erik.
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