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AD9859, further clarifications in OSK mode

Question asked by zuzu on May 9, 2011
Latest reply on May 17, 2011 by DSB

Hello friends,


Still unclear on AD9859, since all family datasheets are iddentical at OSK section. So few questions please:


1. If Shaped OOK is disabled (bypass) from CFR1[25] it means than OSK pin is don't care, amplitude ON-OFF is no more available at all, unless software modifies ASF register. This is correct ?


2. The auto ramp timer increments at SYS CLOCK ? I saw other DDS specifies 1/4 of SYS CLOCK.


3. The "scale-factor" from ASF[15:14] makes internally counter for ramp increment / decrement x time faster ? If I understand well:


- the max. ramp step size is given by ARR which on AD9859 is 256 or in 400MHz period (2.5nS) means 0.64uS

- the slowest ramp is when ASF[15:14] is 1, meaning 1024 steps for full ASF = 0.64 * 1024 = 655.36 uS


Thanks very much for clarifications