The distinguishing features of the CMX649 are the advanced error tolerant voice coding and industry leading low power consumption (drawing an operational 1.9mA at 2.7V), with advanced power-saving options to further battery life conservation in miniature cordless applications, such as ‘in-ear’ hands-free headsets.
The CMX649 offers full-duplex ADM, Continuously Variable Slope Delta Modulation (CVSD) and PCM (linear, A‑law, µ(mu)‑law and linear) operating modes. 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 designs.
Independent Tx and Rx powersave modes also support lowest power operation in all modes. The product’s ability to ‘tune’ the majority of on-chip sections, provides reduced power consumption allowing product design engineers to develop optimal power-requirement strategies tailored to 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.
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).