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Understanding common inter-IC digital interfaces for audio data transfer

Posted: 11 Jun 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Audio system? DSPs? amplifiers? speakers?

As audio integrated-circuit (IC) designs shift to finer geometries, it becomes more challenging to design, and less cost-effective to integrate high-performance analog circuits on the same piece of silicon with high-density digital circuits. Audio system architects are pushing analog portions of an audio signal chain further toward the input and output transducers and connecting everything in between digitally.

As the analog circuits are pushed to the edges of the signal chain, digital interfaces between ICs in the chain become more prevalent. DSPs have always had digital connections, but now digital interfaces are being included on the transducers and amplifiers that usually have had only analog interfaces. A traditional audio signal chain may have analog signal connections between microphones, preamps, ADCs, DACs, output amplifiers, and speakers (figure 1).

Figure 1: Traditional audio signal chain.

IC designers are integrating the ADCs, DACs, and modulators in the transducers on opposite ends of the signal chain, which eliminates the need to route any analog audio signals on the PCB, as well as reduces the number of devices in the signal chain. Figure 2 shows an example of a completely-digital audio-signal chain.

Figure 2: Fully-digital audio signal chain.

There are many different standards for transmitting digital-audio data from one place to another. Some formats, such as I2S, TDM, and PDM are typically used for inter-IC communication on the same PC board. Others, such as S/PDIF and Ethernet AVB are primarily used for data connections from one PCB to another through cabling.

This article will focus on the differences, advantages, and disadvantages of the inter-IC, rather than inter-board, digital audio formats. Choosing audio components with mismatched digital interfaces needlessly complicates the system design; understanding the pros and cons of different interfaces before selecting parts helps to streamline your component selection and ensure that you have the most-efficient implementation of the signal chain.

Inter-IC sound
Inter-IC, more commonly called "I-squared-S" or "I-two-S"), is the most common digital audio format used for audio data transfer between ICs. The I2S standard was introduced by Philips Semiconductors (now NXP) in 1986 and was revised in 1996. The interface was first popularly used in CD-player designs, and now can be found in almost any application where digital-audio data is being transferred from one IC to another. Most audio ADCs, DACs, DSPs, sample-rate converters, and some microcontrollers include I2S interfaces.

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