As audio integrated circuit (IC) designs move to finer geometries, it becomes more difficult 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 towards 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, as shown in Figure 1. 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.