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AD5930 Intermittent Frequency Glitch

Question asked by ngamell on Oct 7, 2013
Latest reply on Oct 11, 2013 by ngamell

Hello,

 

Recently, I have been using your AD5930 Evaluation Board for a prototype, and I have noticed an odd glitch during frequency sweeping.  I am continually bursting two different frequencies using the "Saw-Sweep mode" in the "external increment, external burst control" option.  (The same glitch was appearing in the "external increment, auto-burst control" option as well.)

 

 

What I have found is that intermittently, the sweep of the two frequencies (7.33 MHz and 8.33 MHz) jumps to a third, unknown frequency state.  This state then changes the order at which the bursting occurs.  Attached to this email is an oscilloscope screen-shot of the mysterious frequency.

 

 

My question, then, is have you seen this issue before?  Are there ways I can correct it via programming or set up?

 

 

I can send any additional information you might need to replicate this glitch or help solve this problem. as well.  Below are the SPI commands sent [in order] at power up to the AD5930 chip.  (Note, the SPI frequency is 656 kHz, sweeping from 7.33 MHz to 8.33 MHz, one 1 MHz step.)

 

 

Cntrl_Register = 0x0F73 (24-bit, single register write; DAC enable; Sine wave mode; MSBout enable; burst mode w/ DC mid-point; Burst external; increment external; saw-sweep mode; syncsel disable; syncout disable; reserved bits)

 

 

Fstart_LSB = 0xC793 (7.33 MHz)

Fstart_MSB = 0xD258

 

 

DeltaF_LSB = 0x2EB8 (1 MHz step-size, increasing)

DeltaF_MSB = 0x3051

 

 

Num_INCR = 0x1001 (1 step)

 

 

** From this point, we let the values sit for 1 millisecond, then begin toggling the CTRL line at a frequency of 71.43 kHz (7 microseconds high, 7 microseconds low).  The waveform between cursors "A" and "B" does not look like the other frequencies we were expecting. 

 

 

Any help or direction would be appreciated.  Thank you,

 

 

Nick

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