[time-nuts] GPSDO simulation tool

Charles Steinmetz csteinmetz at yandex.com
Sun Mar 23 16:45:34 EDT 2014

Jim wrote:

>Is a higher degree loop possible while maintaining stability?

Sure.  PLL control loops (and other feedback loops) are often 
designed out to fourth and fifth order.  Very simply put, the 
requirement is that the loop must have a reasonable phase margin at 
the frequency where the gain reaches unity.  For multiple open-loop 
poles (where this condition would not be met), the usual solution is 
to "give back" all but one pole by cancelling them with 
high-frequency zeroes.  All of this can give useful improvements in 
loop gain at low- to mid-frequencies, at the cost of increased 
complexity and greater sensitivity to component tolerances.

Best regards,


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