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What are some common noise issues in audio CODECs and ADCs and how can I help prevent them?
There can be many causes for noise in one’s system. I have listed the most common suspects below (Not in any particular order):
Out of Band Noise is a very common issue and not usually accounted for. Out of Band Noise is high frequency noise generated by the digital switching within the CODEC/ADC. When connecting the analog output to a Class-D amplifier, this noise will get aliased back into the audio band and affect the output. Out of Band Noise can easily be resolved by adding a Low Pass filter at the analog outputs with a cutoff at ~30 kHz.
Incorrectly configuring the PLL and ASI in the CODEC/ADC can also lead to noise issues. Both the PLL and ASI bus offer the ability to be configured multiple ways. It is important to ensure that proper configuration of the two. More information on the PLL and ASI bus can be found in their respective sections in the data sheet.
Noise can also come from the analog/digital power supplies and GND. For power supplies, it is important to properly decouple the supplies with 0.1uF and 10uF capacitors and place them as close to the device as possible. For grounding, we recommend separating the analog and digital grounds and joining them with 0ohm resistors. The analog and digital activity should also be separated with the digital activity on the digital plane and analog activity on the analog plane.
More information on these topics can be found in the following App Note here. Following these recommendations will help prevent noise in and around the CODEC/ADC.
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