Amplitude Modulation in digital domain with DDS

Hi,

You can use Ad9911, and use the test-tone modulation mode. It enables sinusoidal amplitude modulation on the carrier. The carrier is the Channel output in which the frequency can be set via registers. You can then set the register of aux Ch0 to set the magnitude of the modulating signal. You may refer to datasheet (test-tone mode section) for more info.

Hope this helps.

Best Regards,

Sitti

Hi,

Thanks for the info.

I have n't used AD9911 but after glance at the datasheet, it looks like the aux channels can modulate the carrier and I guess the modulating frequency is basically generated by these aux channels themselves by programming the registers. When one writes to these magnitude registers, are the aux channels bypassed and the amplitudes of the primary carrier directly controlled?

In the case I mentioned, the modulating signal (digitally sampled signal) comes from an external device which needs to modulate the carrier generated by DDS.

Best,

Chakravarthy

Hi,

Unfortunately, the aux channels cannot be bypassed. they can only be disabled, but disabling all the 3 aux channels just puts the dds in single-tone mode.

Aside from external VGA, you can change the Rset value that sets the DAC output current. Here are some application notes using this method:

• AM of AD9850
• Amplitude control for AD9834

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