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MAX5880：High-Density Downstream Cable QAM Modulator and Digital Upconverter

Scalable DUC for DOCSIS 3.0-Compliant Edge QAM Devices Generates Up to 128 QAM Channels at 26mW/QAM

The MAX5880 high-density downstream cable QAM modulator and digital upconverter (DUC) performs QAM mapping, pulse shaping, and digital RF upconversion of forward-error-correction (FEC)-encoded data with full agility. The device drives an RF digital-to-analog converter (RF-DAC) to digitally synthesize RF signals with up to 128 DOCSIS-compliant 6MHz QAM channels (or up to 96 8MHz QAM channels) on a single RF port. The DUC device and Maxim's RF-DACs provide high-density QAM modulation with very low power dissipation in a compact 17mm x 17mm footprint. The device accepts FEC-encoded CMOS data (symbols) on up to four 10-bit input ports that accept up to 32 time-interleaved digital data streams each. Each channel features an individually configurable QAM mapper, RRC filter, and arbitrary rate resampler (ARR). The device performs pulse shaping, resampling, interpolation and quadrature modulation of input data, supporting all data rates defined in DOCSIS and DVB-C. A cascade of interpolation filters, complex modulators, and channel combiners allow modulation of the signal to any frequency from 45MHz to 1003MHz. Integrated direct digital frequency synthesizers allow positioning of the QAM channels with a resolution of 125Hz. The interpolation filters and resamplers provide linear phase and excellent gain flatness. Output data from the last modulator is fed to a digital-predistortion (DPD) block that can be used to correct distortion in the RF-DAC and output amplifiers. The output interface to the RF-DAC consists of four 14-bit interleaved LVDS buses that operate up to 1250Mwps each.

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Design kits & evaluation modules

• MAX5880EVKIT

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