Electronic Design

High-Density SoC Makes GPON And FTTH Triple Play Practical And Affordable

With speeds of up to several hundred megabits/s, fiber to the home (FTTH) would be the best broadband service available—if it weren't so expensive. Freescale Semiconductor takes a shot at reducing some of those costs with its MSC7120 chip set.

According to the company, the average U.S. home is going to need as much as 40 Mbits/s to support one HDTV channel, two MPEG2 digital TV (DTV) channels, Internet access, Voice over Internet Protocol (VoIP) phones, gaming, and other services by 2009. And today's infrastructure just can't handle those demands.

DSL only delivers a fraction of that bandwidth, and we're still a few years away from VDSL2. Cable TV comes closer with its DOCSIS 3.0 systems, where channel bonding can boost downstream rates well into the desired range—for a price. Also, hybrid fiber/VDSL2 systems are now showing up as AT&T rolls out its U-verse Internet Protocol TV (IPTV).

FTTH installation can cost as much as $1800 per customer in the U.S. Yet gigabit passive optical networks (GPONs) are reducing some of these costs. Japan and Korea have adopted the Ethernet PON standard, which delivers 1 Gbit/s on the downstream and upstream links. Verizon is installing FTTH with its FiOS system as well. As fiber prices continue to drop, more FTTH will occur.

Freescale's MSC7120 system-on-a-chip (SoC) targets customer premises equipment (CPE) like set-top boxes, which are called optical network terminals (ONTs) in the jargon of PONs. It supports data, voice, and video. It also complies with the ITU's G.984 GPON standard. In fact, it's the latest variation of the standard that started with APON and BPON.

The GPON standard is capable of 2.4 Gbits/s downstream and 1.2 Mbits/s upstream in a PON that can serve up to 64 subscribers on a single fiber. The entirely passive network consists only of the fiber and a number of passive splitters/combiners. GPON's very low cost and near total lack of need for maintenance removes a huge cost from the deployment equation.

The MSC7120 incorporates a Freescale Power Architecture e300 core for control path operation, a dedicated packet engine for the data path, and a StarCoreSC1400 DSP core for VoIP processing. The I/O includes 48 general-purpose I/O pins, UART, SPI, I2C, and timers. Other interfaces include JTAG as well as DDR and DDR2 memory controller interfaces. Its dual 10/100/1000 Ethernet media-access controllers (MACs) support RGMII.

The PON subsystem complies with the ITU-T G.984 GPON standard. It integrates the TC/MAC function, the clock and data recovery (CDR), and the interface to the optical transceiver. Forward error correction (FEC) with AES is included. The housing is a 456-pin thermally enhanced PBGA package. Samples are available now, as are reference designs and an evaluation board (see the figure). Check with Freescale for pricing.

Freescale Semiconductor

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