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ST70134 Folha de dados(PDF) 4 Page - STMicroelectronics |
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ST70134 Folha de dados(HTML) 4 Page - STMicroelectronics |
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4 / 8 page  ST70134 - ST70135A 4/8 Discrete MultiTone Digital Modem (ST70135A) The DMT modem has been developed in HCMOS6 (0.35 µm) technology. It performs PMD (Physycal Medium Dependant) sub-layer and TC (Transmission Convergence) sub-layer functions. In other words we can split the chip into two separate blocks: the first one which carries out modem functions (PMD sub layer) and a second one in charge of ATM framing. The chip is controlled and programmed by an external processor and is seen as a memory mapped device. MODEM Functions The modem part of the chip includes all the necessary blocks needed for digitally DMT mapping and demapping. A 14-bit code for every carrier allows constellations with up to 16383 points. Internally, digital filters carry out Time Equalization to reduce the effects of the inter symbol interference. That is followed by Fast Fourier Transform (in transmit direction an Inverse FFT is performed) in order to change from time domain to frequency domain. Afterwards a Frequency Equalization cuts down carrier by carrier the channel distortion, signal’s amplitude attenuation and phase rotation. By efficient algorithms, this block drives, through the ST70134’s integrated VCXO controller, the NT crystal oscillator which comes up in an excellent synchronisation (less than 2ppm) with ATU-C. FRAMING Functions ST70135A performs framing functions for generic and ATM TC sub layers. ATM TC sub layer performs cell level functions: delineation, idle cells or unassigned cells insertion/extraction, payload scrambling, Header Error Correction (HEC) check and data frame generation. ST70135A DMT modem main features: – Time-domain equalisation – Rotor and frequency-domain equalisation – Decimation, interpolation – FFT and IFFT – Mapping/demapping over 256 carriers – Trellis coding and decoding using Viterbi algorithm – Error and noise monitoring on individual tones – Reed-Solomon encoding and decoding – (De) framing and (de) interleaving – Cell HEC generation/verification – Payload (de) scrambling – ATM cell insertion/extraction – Idle &/or Unassigned cell insertion/filtering – VPI/VCI filtering – UTOPIA interface (Level 1 or 2) – Microcontroller interface with 16-bit multiplexed address/data bus and big/little endian format supported – JTAG test port – Single 3.3V supply, 1.0W – PQFP144 (28 x 28mm body, 0.65mm pitch) Figure 3 : DMT Modem block diagram FFT Rx DSP FE DEMAPPER VITERBI CELL BASED FUNCT. DE- FRAMER Rx INTERF. INTERLEAVED FAST SIGNAL MONITORING & FEQ UPDATE & DPLL ADSL AFE PMD SUBLAYER TC SUBLAYER ATM (UTOPIA) IFFT Tx DSP FE MAPPER VITERBI R/S CODER CELL BASED FUNCT. FRAMER Tx INTERF. FAST INTERLEAVED R/S DECODER |
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