CMX638L4

Product description

The CMX638 is a flexible, high integration, high performance, RALCWI (Robust Advanced Low Complexity Waveform Interpolation) Vocoders, offering near toll quality voice at very low bit rates. A Forward Error Correction (FEC) engine provides optimum performance in real life applications. The RALCWI Vocoder comprises four independent functions which are selectable by the host: Voice Encoder, FEC Encoder, Voice Decoder and FEC Decoder. The CMX638 is a full-duplex Vocoder with integrated voice CODEC.

The CMX638 operates from a dual power supply (1.8V and 3.3V) and are available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages.

In encode mode, the voice encoder uses a 20ms voice frame size with two programmable bit rates: 2400bps or 2750bps. The optional FEC encoder performs channel coding of the encoded voice (2400bps or 2750bps, depending on the selected mode) and forms an encoded, interleaved bit-stream of 3600bps (216 bits per 60ms packet or 288 bits per 80ms packet). The FEC operation utilises a packet of either 3 or 4 x 20ms Vocoder frames to provide optimum error correction performance.

In decode mode, 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 2400bps or 2750bps rate, depending on the selected mode. The FEC decoder can optionally use "soft decision" metrics to improve its decoding ability. The voice decoder then converts the error-corrected bit-stream back into a digitised voice signal.

Soft Decision Decoding (SDD), Discontinuous Transmission detection (DTX), Voice Activity Detection (VAD) and Comfort Noise Generation (CNG) functions are also included, to further enhance the overall performance. Single (STD) and Dual (DTMF) Tones can be detected and sent separately in the coded bit stream, then regenerated at the far end.

Features

• Near Toll Quality RALCWI Coding Algorithm
• Multiple Bit Rate Modes: - 2400 or 2750 bps - 3600 bps with FEC Enabled
• 4-bit Viterbi Soft Decision Decoding
• 4-bit Viterbi Soft Decision Decoding
• Integrated Audio CODEC (CMX618/CMX638 only)
• Integrated Input and Output Channel Filters
• 20ms, 40ms, 60ms and 80ms Packet Lengths
• No Licensing or Royalty Payments
• Ancillary Audio Functions: - Voice Activity Detector - Comfort Noise Generator - DTMF and Single Tone Regeneration
• 1.8V Low Power Operation, 3.3V Tolerant I/O