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AD9910 Phase coherent RAM profile switching

Question asked by bibi242 on Mar 7, 2017
Latest reply on Mar 14, 2017 by KennyG

Hello All

 

We are currently using AD9910 in-order to generate RADAR waveform which switches between  a tone and  LFM. LFM is 3 MHz bandwidth and tone is 4 MHz away.

lfm & tone

Currently this was implemented using  RAM mode of DDS with two profiles (profile0 and profile 1)which  are switched w.r.t PRT connected to profile pin PS0 as suggested by Kenny G DDS AD9910- switching from single tone to ramp generation mode .

 

Profle 0 of RAM contain start stop address of 250 LFM points and RAMP UP mode is used. RAM address step rate is adjusted so that RAM sweeps the LFM points in 10us.

Profile 1 of RAM contain address of  single tone freq and I am usnig DIRECT SWITCH mode.

 

These two profiles are switched based on PRT connected to PS0 pin of DDS.

 

My doubt is if it is possible to maintain phase coherence between LFM and Tone. The only option I found is to set auto clear phase accumulator bit in CFR1 to '1'. Though phase is resetting in each profile change but waveform doesn't seems to begin from zero phase or fixed phase position. 

 

Other than RAM mode do I have any other option in this scenario?

 

Please give some suggestions on this

 

Kindly forgive my bad English

 

Thanks

Vipin

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