Analog Angle Article

AFE ICs tackle DSL variations

Santa Clara, Calif–DSL offers high speed connectivity potential, but the many variations can drive designers in circles while trying to meet the requisite technical requirements. Two Analog Front End (AFE) ICs from PMC-Sierra, Inc , Sunnyvale, CA make the task easier. For VDSL2 (100 Mbps upstream/downstream) and ADSL2+ Customer Premises Equipment (CPE), the PM4380 CMOS device meets the challenges of low signal distortion, noise density, and power consumption, to achieve increased loop length and data rate.

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The PM4380 Analog Front End from PMC-Sierra provides a nearly compete solution to VDSL2/ADSL2+ implementations, requiring an xDSL hybrid, transformer/lighting protection, and line splitter to complete the line interface.

According to Hamish Dobson, Manager of Product Marketing, the PM4380 is fully backwards compatible with ADSL2+, ADSL2, and ADSL systems, and includes user-programmable continuous-time and digital filters that can be matched to different bandwidths, high-linearity line drivers which maximum upstream bit rate, and a low-noise amplifier to for maximum downstream bit rate. Dave Paulizzi, Product Marketing Engineer, notes that the receive noise chain has input-referred noise better than -150 dBm/Hz, 10 dB better than the industry's typical -140 dBm target value.

Signal distortion is specified using multitone power ratio (MTPR), which is a better indicator of performance than spur free dynamic range (SFDR), according to Dobson. The A/D and D/A converters have between 12 and 14 effective bits, depending on operating mode, while the line drivers can drive +14.5 dBm onto a 100-ohm line. Also within the IC is a 16-bit digitally controlled crystal oscillator with frequency resolution better than 0.02 ppm.

A similar IC, the PM4381 AFE, is focused on ADSL2+, ADSL2, and ADSL systems, and can be paired with PMC-Sierra's MSP7120 as part of a DSL chipset. The 3.3/5V ICs are priced at $3.90 for the PM4380 and $$3.00 for the PM4381, in 10,000 pieces.

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