Document
CML Microcircuits
COMMUNICATION SEMICONDUCTORS
CMX608/CMX618/ CMX638
RALCWI Vocoders
D/608_18_38/11 September 2014
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
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
Small 48-pin LQFP and VQFN Packages
Provisional Issue
Applications
Digital PMR, LMR, Voice Radio Digital Trunking DMR TDMA
DMR FDMA, dPMR Digital Voice Scrambling and Encryption Digital WLL Voice Storage and Playback Systems Regenerative Digital Voice Repeaters Messaging Systems VoIP Systems Voice Pagers Half-Duplex Vocoding (CMX608/CMX618) Full-Duplex Vocoding (CMX638 only)
1. Brief Description
The CMX608/CMX618/CMX638 are 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 CMX608 and CMX618 are half-duplex Vocoders and the CMX638 is a full-duplex Vocoder with integrated voice CODEC.The CMX618 includes an integrated voice CODEC, offering a complete analogue voice to low bit rate vocoded data function, with integrated channel filters removing the need for external components, whereas the CMX608 requires an external voice CODEC.
CMX608/CMX618/CMX638 operate 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.
Continued overleaf .....
2014 CML Microsystems Plc
RALCWI Vocoder
CMX608/CMX618/CMX638
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 bitstream, then regenerated at the far end.
New features and enhancements to existing functions may be provided from time to time, expanding the capabilities of the Vocoder. These are provided as Function Images™, a hex format file that can be loaded via the C-BUS at run-time. Function Images™ can be downloaded from the CML Portal, a secure area of the CML website. Details of currently available Function Images™ can be found in the CMX608/CMX618/CMX638 Product page on the CML website.
2014 CML Microsystems Plc
2
D/608_18_38/11
RALCWI Vocoder
CMX608/CMX618/CMX638
Section
CONTENTS
Page
1. Brief Description ..................................................................................................................... 1
2. Block Diagram ......................................................................................................................... 5
3. Signal List ................................................................................................................................ 6
4. External Components............................................................................................................. 9 4.1. PCB Layout Guidelines and Power Supply Decoupling ................................................. 11 4.2. Audio CODEC External Components (CMX618/CMX638 only) .................................... 12
5. General Description .............................................................................................................. 13 5.1. Initialisation .................................................................................................................... 14 5.2. Enc.