AD1853 introduces spurs when given a DC offset?

Hello Ryan,

It would be good to know what sampling rate you are running at, but basically you are seeing idle tones. One of the methods for eliminating idle tones is to add a DC offset which will push the tones up out of the audio band. This is why you see it shift higher the more DC you add. The nature of idle tones will change with the input data so that behavior is to be expected.

Adding noise is another way to prevent idle tones but this will obviously reduce your SNR of the system. Adding a DC offset will reduce your headroom a little but it is often not an issue depending on the application.

You mentioned the "full 20 kHz" signal. So am I to assume you are running at 44.1 kHz? Then adding some DC or noise to "push" the idle tones over 40 kHz will make it easy to filter out with a simple RC filter on the output.

Thanks,

Dave T

Hello Ryan,

It would be good to know what sampling rate you are running at, but basically you are seeing idle tones. One of the methods for eliminating idle tones is to add a DC offset which will push the tones up out of the audio band. This is why you see it shift higher the more DC you add. The nature of idle tones will change with the input data so that behavior is to be expected.

Adding noise is another way to prevent idle tones but this will obviously reduce your SNR of the system. Adding a DC offset will reduce your headroom a little but it is often not an issue depending on the application.

You mentioned the "full 20 kHz" signal. So am I to assume you are running at 44.1 kHz? Then adding some DC or noise to "push" the idle tones over 40 kHz will make it easy to filter out with a simple RC filter on the output.

Thanks,

Dave T