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AD9834: Settling Time Between Frequency Change

Question asked by languer on Jun 14, 2011
Latest reply on Jul 11, 2011 by languer

What should I expect the settling time to be between frequecny changes on the AD9834? For example, we have an application where we swing the AD9834 output from 10.697MHz to 10.703MHz (using a 67.2MHz MCLK). From the datasheet I would expect this to be 7-8_MCLKs (or under 1us); but I am measuring just over 10us both using the FM demodulator on a Signal Analyzer, or using Agilent's 5052B SSA.

 

On a related question, when I filter the DDS output with a XTAL filter the settling time incresases significantly. It doesn't seem the increase is just due to group delay, but I may be wrong (the filter GD is 30us, the frequency change settling time is around 65us). Does anybody knows what the driver(s) for this increase (GD, Q)? We are going to try a wider filter to see if we get different responses.

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