Vocoder IC offers full duplex capability

Maldon, Essex, England—CML Microcircuits has added to its voice coder/encoder (vocoder) family a robust advanced low complexity waveform interpolation (RALCWI) IC dubbed the CMX638 that offers full duplex capability.

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.

The voice encoder uses a 20ms voice frame size, with three programmable bit-rates—2050bps, 2400bps or 2750bps. The optional FEC encoder performs channel coding of the encoded voice (at the rate selected) and forms an encoded, interleaved bit-stream of 3600bps (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 2050bps, 2400bps or 2750bps, 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.

Datasheets: Click here.


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