Ultra-low power voice codec for ‘always on’ applications

David Brooke, Product Manager Wireless Voice and Data, CML Microcircuits, explained: “The pure voice codec has been under served for many years, in terms of investment from the industry at large, because the majority of the focus has been on multimedia codecs for smart phones. This has left OEMs with no practical way of benefiting from the significant advancements that have been made in process technology, as well as MEMS microphone and speaker technology over the same timeframe. With the CMX655D we are redressing that, by bringing the voice codec into the smart generation.”

The CMX655D features two independent microphone channels capable of operating in full duplex mode while maintaining relative signal phase, enabling one device to support two way communication while simultaneously applying echo cancellation, for example.

The voice filters offered by the DSP include 300Hz to 3.4kHz for classic telephony and 50Hz to 7kHz for High-Definition audio, while all signal paths supports audio bandwidths up to 21kHz at sample rates of eight, 16, 32 or 48k samples/s. As a traditional telephony codec, the CMX655D supports A-law and µ-law companding.

The two parallel channels feature completely separate signal paths but share a common serial audio interface, which supports I2S (the Inter-IC Sound serial bus designed for digital audio devices) as well as I2C and SPI interfaces for device control.

The CMX655D is supported by a wide range of development tools including an EV6550D evaluation kit and is available now in a small four by four millimetre QFN package.