PDF AT2004 Data sheet ( Hoja de datos )

Número de pieza	AT2004
Descripción	4 Channel ADPCM Processor
Fabricantes	Atelic Systems
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No Preview Available ! AT2004 4 Channels ADPCM Processor with Echo Cancellation and Conferencing Atelic Systems, Inc. Description AT2004 Application Note Preliminary 4 Channels ADPCM Processor with Echo Cancellation and Conferencing Version 1.0 January 29, 2001 The AT2004 is a four full-duplex channels, ADPCM processor with conferencing and echo cancellation capabilities. It follows the G.726 ITU Standard for ADPCM compression for 40k, 32k, 24k and 16k bitrates with selectable µ-law and A- law input/output. It conforms to ITU G.165/G.168 Digital Adaptive Echo Canceller specification for line echo delay up to 20ms. Using the command serial interface, each individual half-channel can be independently configured for ADPCM, conferencing and echo canceling features. Features • 4 full channels of ITU G.726 ADPCM • 4 full channels of ITU G.165/G.168 complia nt echo cancellation with up to 20ms echo delay • Fast and robust convergence for adaptive echo canceller, even in the presence of background noise • Nonlinear processing with adaptive suppression threshold and comfort noise generation for echo canceller • Per channel selectable µ-Law and A-law input/output • On-chip time slot assignment • Available internal clock generator and frame sync. generator • Simple 3-wire serial command port for chip configuration • Conferencing capabilities for up to 3 additional sound sources Applications • DECT • VoIP / VoDSL • Wireless telephone systems • Wireless PBX systems Default Settings • 4 channels of µ-law PCM input on Xin in time slot 0, 1, 2, 3 • 4 channels of the corresponding ADPCM output at 32kbps on Xout in time slot 0, 1, 2, 3 • 4 channels of ADPCM input at 32kbps on Yin in time slot 0, 1, 2, 3 • 4 channels of corresponding PCM µ-law output on Yout in time slot 0, 1, 2, 3 • Echo cancellation enabled for four channels • Conferencing disabled Note: To change the default settings, commands could be sent through the 3-wire interface. Page 1 of 25 ©2001 Atelic System, Inc 1 page AT2004 4 Channels ADPCM Processor with Echo Cancellation and Conferencing Echo Canceller Block Diagram: Dc_rmv Comfort Noise NLP_flag EC Bypass DC Remover - NLP M U X Stepsize Freeze Adaptive Filter Dc_rmv DC Remover Double Talk Detector Narrow Band Signal Detector Disabling Tone Detector No. 5, 6, 7 Signalling Tone Detector Tone_flag Note: • A dotted line with arrow mark indicate the control bit in the per channel control command, such as LawP, EC reset, LawA, ADPCM bypass, ADPCM reset, Channel bypass, Dc_rmv, Comfort noise, NLP_flag, EC bypass, Stepsize, Freeze and Tone_flag. Please refer to page 10, 11 and 12 for detail information. • Only one full channel is shown. AT2004 has additional capability to process up to 4 full channels simultaneously. Page 5 of 25 ©2001 Atelic System, Inc 5 Page AT2004 4 Channels ADPCM Processor with Echo Cancellation and Conferencing Stepsize2/Stepsize1 Description 0 0 Gain is +3dB of normal case 0 1 Normal case (default setting) 1 0 Gain is -3dB of normal case 1 1 Gain is -6 dB of normal case Default: 01 for normal case. Stepsize control the adaptation speed of adaptive filter. Default setting is the empirically chosen optimal setting. Reduce the stepsize will make echo canceller more stable (robust), however, it will take longer time to converge. Increase the stepsize will have opposite effect. Comfort_noise2/Comfort_noise1 Description 0 0 No comfort noise generation 0 1 Pseudo random noise 1 0 Noise generated by clipping 1 1 Not defined Default: 10 for noise generated by clipping. AT2004 supports two comfort noise generation schemes. One is by generating pseudo random noise with energy matched to the energy of background noise. The other one is by clipping the signal to the level of background noise. The later one is chosen as default setting because it sounds subjectively better. Dc_rmv Description 0 Disable Dc remover 1 Enable Dc remover Default: 1 NLP_flag Description 0 Disable NLP processing 1 Enable NLP processing Default: 1 NLP (Non Linear Processing) is to block the small amount of residual echo which may be still audible. When NLP is enabled, user can further enable or disable comfort noise generation. When NLP is disabled, there will be no comfort noise generation. Freeze Description 0 Normal operation 1 Coefficient of adaptive filter is frozen (no adaptation) Default: 0 EC Description bypass 0 Normal operation of echo cancellation 1 Echo canceller’s output is derived directly from dc remover output Default: 0 Tone_flag 0 1 Default: 1 Description Disable tone detection Enable tone detection Page 11 of 25 ©2001 Atelic System, Inc 11 Page

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