Robust and innovative wireless-headset voice codec

The CMX649 is an innovative Adaptive Delta Modulation (ADM) voice codec – a complete voice system on a chip that is designed to serve in a multitude of wireless voice link applications. This innovative chip offers robust, error tolerant voice coding, low power consumption and whole host of advanced features.

Primarily intended for cordless headsets and ‘hands-free’ systems, the CMX649 consumes an ultra-low voltage (drawing only an operational 1.9mA at 2.7V), with advanced power-saving options for further battery life conservation in miniature cordless applications, such as, in-ear hands-free headsets.

Low power and versatility are just two of the distinguishing features of CML’s CMX649. A multi-mode audio codec IC for wireless digital voice/audio communication, the CMX649 is ideal for consumer and industrial applications including cordless telephones, PC speech-to-text applications, digital voice storage/playback, telematic voice recognition systems, Digital Radio (TDD) and much more.

For further informatioThe CMX649 offers full-duplex ADM, Continuously Variable Slope Delta Modulation (CVSD) and PCM (linear, A?law, µ(mu)?law and linear) operating modes. CMX649 operating modes and algorithms are user-configurable, so as to select the best data rate and voice quality for each application. Robust ADM coding (e.g. CVSD) reduces host protocol and software burdens by eliminating the need for forward-error-correction, framing protocols and algorithm processing. Acceptance of the CVSD algorithm has been widely promoted by its inclusion in the Bluetooth™ standard. One particular CMX649 CVSD mode provides 64kb/s coding to support Bluetooth™ compatible customer designs.


Independent Tx and Rx powersave modes also support lowest power operation in all modes- lower than that of competitors. The product’s ability to ‘tune’ many on-chip sections to provide reduced power consumption allows product design engineers to develop optimal power-requirement strategies for specific applications.

Integrated on-chip functions eliminate the need for external circuits, including: DSP, audio-gain, sidetone, mic-gain, audio filtering and PLL data clock recovery. With its popular C-BUS serial interface, the CMX649 reduces the cost, size and design effort required to interface analogue ‘voice’ signals to digital wireless transceivers.

Additional CMX649 features include a programmable voice activity detector (VAD) with adjustable threshold level and attack/decay times, a transcoder to convert between different voice coding schemes and a selectable digital scrambler for coded signal privacy and efficiency in modulation.

CVSD/ADM coding offers many advantages to wireless voice communications projects, major among these are: ‘Best-fit’ and versatile solutions to most over-air requirements, good quality output audio, high tolerance to data errors and no need for complex error correction schemes. The CMX649 adds total dynamic operational versatility to this list.

The CMX649 is available in compact 20- pin plastic SOIC and TSSOP packages, and an evaluation kit is available (DE6491 Wireless Voice Link Demonstration Kit).
Please contact Mark Channen at CML Microcircuits UK Ltd for further information.