AnsweredAssumed Answered

AD9958 linear sweep problem

Question asked by jeffreyprinzie on Mar 21, 2013
Latest reply on Mar 22, 2013 by jeffreyprinzie

Dear,

 

I am building a circuit with 2 channels.  Both at fixed frequency but CH1 has a linear phase shift 0-360° and is used as phase interpolator.

 

The interface to the DDS works. I can program both frequency correctly.

 

The problem comes when i try the linear sweep with NO-DWELL active.

 

The code initializes the CTFW0 frequency register to 12.5MHz for both cannels. (that works) .

 

Then an initialisation code is invoked that writes following registers:

 

Select channel 1

 

-CPOW0

     0x0000 (S0)

-CW1

     0xFFFFFFFF   (E0)

-RDW and FDW

     0x00000100

-LSRR (40 ns per increment)

     0x0505

 

-CFR:

     AFP=11 (phase)

     LinearSweepNoDWELL=1

     LinearSweepEnable=1

  

     rest is zero  (including open[12:11] bits)

 

 

In FR1 is set the profile pin configuration bits all 0, also RU/RD bits, because I dont use modulation.

 

 

 

In the datasheet it is noted tha P1 should be used as profile pin, but I tried all profile pins, no sweep is show, just steady sines at 12.5MHz having constant phase.

 

do you have any idea what can be wrong?

 

Specs:

3.3V profile pins

25MHz Xtal

PLLx20

 

Thanks in advance

 

Jeffrey

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