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AD9959 Frequency Modulation


I am trying to use an AD9959 to frequency modulate and I am experiencing difficulty getting it to do so continuously.  In the evaluation software I currently have a 500 MHz ref clock.  I have RU\RD diabled and I have 2-level mod selected.

In the channel control I have channel2 selected with Frequency Modulation output type.

On channel 2 I am trying to modulate a 80 MHz frequency.  So say I want both 84 and 80 MHz output signals  I only see the frequency change when I manually hit P2 on the Profile and RURD Pin Control.  And in my mind the output signal should carry both frequencies not a single one.  I'm looking at this on a spectrum analyzer and not seeing both frequencies.  Any advice would be appreciated.

Thank you.

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  • Hi Prerna,

    The "FM" issue mentioned in this thread is not a problem with the GUI. The intent of the GUI is to demonstrate functionality, which it does. That is, frequency modulation is demonstrated via the GUI, but the modulation rate is constrained to toggling the P0-P3 pins via mouse clicks. As such, the modulation rate is quite low per the response of the GUI to mouse clicks.

    Realtime FM requires control of the P0-P3 pins via external digital signals.

  • Hi Kenny,
    Could I do external modulation without resorting to manual control? 

  • No. The only mechanism for external control of the EVB is to switch the EVB to full manual control.

    The AD9959 does offer an automated FM mechanism via the Linear Sweep mode. However, the modulation is constrained to linear FM. That is, the frequency vs time profile is a constant slope or ramp.

    Although not a solution to the problem, I've attached a simplified block diagram of the EVB that shows the connectivity between the Cypress chip, AD9959, tristate buffers and the header row connectors (U5, U13). This might help you figure out how to hack the board to gain the desired functionality.