Vocoder IC rolls with full duplex capability

A robust advanced low complexity waveform interpolation (RALCWI) voice coder/encoder (vocoder) IC has been introduced by CML Microcircuits PLC. The CMX638 offers full duplex capability, a new capability to CML's previous offerings.

CML now offers the CMX608, CMX618 and CMX638 high performance vocoders with an FEC engine that each offers near toll-quality voice performance at very low bit-rates. The RALCWI vocoder consists of four independent functions that are selectable by the host, including voice encoder, FEC encoder, voice decoder and FEC decoder.

The CMX608 and CMX618 are half-duplex ICs, while the CMX638 offers full-duplex capability. The CMX618 and CMX638 include an integrated voice codec, for complete analog voice to low bit-rate vocoded data function (with integrated channel filters, removing the need for external components). The CMX608 is offered without the codec.

Bit rate options
The voice encoder uses a 20ms voice frame size, with three programmable bit-rates—2,050bit/s, 2,400bit/s or 2,750bit/s. The optional FEC encoder performs channel coding of the encoded voice (at the rate selected) and forms an encoded, interleaved bit-stream of 3,600bit/s (216 bits per 60ms packet or 288 bits per 80ms packet). The FEC operation uses a packet of either 3 or 4 x 20ms vocoder frames for optimum error correction performance.

The optional FEC decoder performs de-interleaving and channel decoding of the coded bit-stream (216 bits per 60ms packet or 288 bits per 80ms packet) and forms an error-corrected bit-stream of encoded voice at 2,050bit/s, 2,400bit/s or 2,750bit/s, depending on the mode selected. The FEC decoder can optionally use 'soft-decision' metrics to enhance its decoding ability. The voice decoder then converts the error-corrected bit-stream back to a digitized voice signal.

All three products operate from dual power supply (1.8V and 3.3V), and are available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages.

- Ismini Scouras
eeProductCenter