Audio ADC buffer design secrets: Interfacing to audio ADC sampling circuits

  
There are several aspects of audio converter design that are generally not well understood but have a dramatic impact on performance, both measurable and audible. Audio converter IC manufacturers generally give circuit recommendations to address these issues but rarely discuss the reasoning behind these suggestions, how performance is affected and why it is important to follow the rules.

However, once a designer has an insight into the issues, it is possible to identify the compromises that often exist in the manufacturers recommendations. This can lead to intelligent insights to lower cost, or in some instances, improve performance.

One of these areas is interfacing to the sampling networks of analog-to-digital-converters. Today's high-performance A/D converters are based on highly oversampled multi-bit delta-sigma conversion with sampling circuits that operate at frequencies several orders of magnitude beyond the audio range. An understanding of how to properly interface to these networks is probably the least understood topic in A/D systems design and remains one of the "magical" areas of audio circuit design.

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