Simple ways to manage different clock frequencies of audio codecs

Carlos Azeredo-Leme, Analog Design Senior Staff, Synopsys Inc.
EETimes (10/26/2011 10:18 AM EDT)

Audio processing is essential to many consumer electronic applications such as mobile phones, MP3 players and a host of other products. While size and power consumption are often critical SoC design requirements, the market demands high-quality high fidelity (Hi-Fi) audio capabilities. To meet this consumer demand, designers are now embedding audio codecs into their next-generation, advanced SoCs.

The audio codec creates the interface between the digital host processor and the audio transducers, such as microphones and speakers. It is also responsible for several routine audio functions, thereby alleviating the workload on the host processor.

The clocks required by the data converters on an audio codec depend on the audio material sampling rates as well as on the clocks available on the host application and SoC. The combinations are quite complex due to the multitude of audio sample rate options and available host clocks. To further complicate matters, in audio-video (A/V) applications, the audio clocks need to also be synchronized with the video clocks required by the video data converters. Therefore, many designers are confronted with complex choices when deciding on trade-offs to minimize system costs related to clock generation and interfacing a multitude of sample rates.

The digital filters play an important role in synchronizing the different clocks because they process the digital samples between the digital audio interface and the audio data converters, and therefore, can perform sampling rate conversions. This article will review the functions of digital filters in audio codecs and will provide several examples to illustrate how they can interface to a range of sample-rates and clock environments.

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