RALCWI family grows with duplex vocoder IC

6 August 2008 Telecoms, Datacoms, Wireless, IoT

CML Microcircuits has added a new RALCWI integrated circuit to its vocoder family.

The new CMX638 is a flexible, highly integrated, high performance duplex vocoder, utilising RALCWI (robust advanced low complexity waveform interpolation) technology. This expands the vocoder family which offers near toll-quality voice performance at very low bit-rates.

A forward error correction (FEC) engine provides optimum performance in real-life applications, with the RALCWI vocoder being comprised of four independent functions, which are selectable by the host: Voice Encoder, FEC Encoder, Voice Decoder, FEC Decoder.

The CMX638 offers full-duplex capability and includes 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 voice encoder uses a 20 ms voice frame size, with three programmable bit-rates (2050, 2400 and 2750 bps). The optional FEC encoder performs channel coding of the encoded voice and forms an encoded, interleaved bit-stream of 3600 bps (216 bits per 60 ms packet or 288 bits per 80 ms packet). The FEC operation utilises a packet of either three or four x 20 ms vocoder frames for optimum error correction performance.

The optional FEC decoder performs de-interleaving and channel decoding of the coded bit-stream and forms an error-corrected bit-stream of encoded voice at 2050 bps, 2400 bps or 2750 bps, 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 digitised voice signal.

For optimum voice performance the following functions are included: soft decision decoding (SDD); discontinuous transmission detection (DTX); voice activity detection (VAD); comfort noise generation (CNG); single (STD) and dual (DTMF) tones (can be detected, sent separately in the coded bit-stream, then regenerated at the far-end).

Vocoder applications include voice storage and playback devices, VoIP, voice pagers, digital WLL, digital PMR/LMR, voice radio, digital trunking, regenerative digital voice repeaters, digital voice scrambling and encryption, and much more.

The device operates from a dual 1,8 V and 3,3 V power supply, and is available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages.

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