Electronic Design

Low-Power Three-Chip Set Handles Four ADSL G.dmt/G.lite Lines

The MTK-20450 DynaMiTe is a four-channel, rate-adaptive, ADSL modem chip set for central-office (CO) equipment. Other target markets include DSL-access multiplexers, next-generation digital loop carriers, ADSL line cards for ATM switches and routers, and manufacturing test equipment.

By definition, a CO features high-density/multiple lines, limited space, and the traditional line-card model. This greatly limits power consumption, board space, and the cost of operation when spread out over millions of lines. Additionally, flexibility is essential for service providers to allow tiered services for varied customer requirements and tariff levels, as well as multiple virtual connections per customer. All this must be provided over extended distances, beyond the theoretical limitation of 18,000 ft.

The DynaMiTe tackles these problems with a three-chip, four-line ADSL solution that occupies a total board footprint of only 7.75 in.2—including the discrete AFE and line driver. Further board-space reductions are possible with hybrid AFE modules. It consumes less than 0.5 W per line, which is a full 50% reduction over its previous iteration, the MTK-20150.

This fully rate-adaptive card also supports multiple standards, including ANSI T1.413 Issue 2, ITU G.992.1 (G.DMT), ITU G.992.2 (G.lite), and ADSL over ISDN. With 24-AWG wire, it reaches up to 26,000 ft., or 18,000 ft. with 26 AWG. At 5000 ft., the data rate is over 8 Mbits/s downstream and 832 kbits/s upstream (26 AWG). This drops to 3 Mbits/s by 720 kbits/s at 12,000 ft.

The device itself comprises a quad AFE (MTC-20454), a quad DMT modem chip (MTC-20455), and a single, ARM-7-based MCU (MTC-20136). The all-CMOS AFE features AGC amplifiers, low-pass filtering, echo cancellation, a 12-bit digital-to-analog converter sampling at 8.8 MHz, and a 13-bit analog-to-digital converter that also samples at 8.8 MHz. The device comes in a 100-pin TQFP.

The modem chip uses a QAM mapper/demapper with 14-bit coding per tone, and it implements the framing functions for the generic and ATM transmission-convergence layers. Several framing variants are implemented to comply with various standards. A UTOPIA interface is included. This chip is packaged in a 144-pin PQFP or MBGA.

The transceiver controller runs all of the control, setup, and interfacing. It features a modem command interface, an 8-bit parallel bus, a serial bus, and a dual-port RAM mailbox. This chip also comes in a 144-pin PQFP or MBGA.

The DynaMiTe comes with a complete reference design, with full schematics and bill of materials, as well as a high level of support. Reference designs are available now. Evaluation boards will be out in June. Samples will be available by July. Full production is expected by November. Contact the company for pricing information.

Alcatel Microelectronics USA, 1225 N. Alma Rd., Richardson, TX 75081; (972) 996-4458; fax (972) 996-2503.

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