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AD9835 noise

Question asked by gerard on Apr 28, 2014
Latest reply on Apr 28, 2014 by sitti

Hi,

 

I'am using an AD9835 to generate a sine wave of 875kHz. The Clock of the DDS is 50MHz. This signal is amplified and travels through a sensor and is rectified and the resulting signal is filtered with a lowpass filter -3dB@10Hz, DC is subtracted and the result is gained 100x.

This results in a DC signal with a unwanted noise signal of 3.14Hz Vtt= 160mV. Tuning the DDS 875.001kHz and the noise signal is gone and system noise is 20mVtt. I guess the noise signal is caused by intermodulation.

 

Is there a way to predict which frequencies have large noise? I noticed all integer numbers of the 50MHz clock have a large noise amplitude.

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