Feature

Seeking the secrets of a satellite receiver

DirecTV set-top-box design focuses on modularity for the mass market.

By Brian Dipert, Senior Technical Editor -- EDN, 1/18/2007

PHOTO GALLERY Click on an image for an extreme closeup. The D11-500   Main board with access card inserted. Main board without access card. Back-panel connections. Main board with tuner daughterboard flipped over. Interchangeable cosmetic front panel. Front of unit with front panel removed, showing IR receiver (right) and light pipe (left).

My wife and I are currently enjoying two concurrent six-month free subscriptions to DirecTV, including hardware, the outcome of a "spam fax" class action lawsuit filed against the company several years ago (and a reflection of the two fax lines at my residence that got spammed). A DirecTV D11-500 satellite receiver currently sits on our living room's home-theater cabinet, but I've dissected its predecessor, a D11-100, for your voyeuristic enjoyment. What's inside the svelte, silver, satellite-satiated case?

The multimedia processing heart of the D11-100, whose system-board topside I've snapped in both access card-inclusive and -exclusive variants, is a Broadcom BCM7312 single-chip satellite set-top decoder IC, which the company publicly unveiled in late November 2004. This device single-handedly offers a lengthy list of functions:

• An integrated RF tuner, supporting 950- to 2150-MHz inputs
• An all-digital 15- to 20-Mbaud variable-rate receiver with integrated 7-bit ADCs and a FEC (forward error correction) decoder
• A DirecTV- and MPEG-compliant data-transport processor with DirecTV A/V security capabilities
• MPEG-ATSC compliant audio/video decoders, supporting MPEG Layer 1 and 2, Dolby AC-3 and compressed PCM audio, and MP@ML (main profile at main level) MPEG-2 video.
• A 2-D graphics engine that supports multiple rendering layers, also handles video scaling, and includes a PAL/NTSC/SECAM encoder, and
• Coordinating the whole show, a 266-MHz MIPS32 CPU core capable of running MIPS16e Application-Specific Extension compressed code and including MMU and EJTAG support.

Note that since the D11-100 is a standard-definition satellite receiver, it offers no MPEG-4-decoding capabilities.

The memory subsystem includes both volatile and nonvolatile flavors; a Hynix 2.5V, 150 MHz 256 Mbit DDR SDRAM (16-bit data interface, TSOP packaging) and a cryptically-marked, BGA-packaged device with a "FW603" firmware code and handwritten "FT" ("firmware tested"?) initials on its topside. A "M^T" logo in one corner suggests that this latter device may come from Micron Technology and, because DirecTV set-top boxes are over-the-air reprogrammable, I presume this device is at a minimum a single-die flash memory. Without tearing the BGA package apart, I don't know for sure, but I suspect it may include dual flash memory die (one for the current firmware image, the other for the upgrade image, with redundancy to ensure a failsafe upgrade methodology). Complementary SRAM and flash-memory die are another possibility.

Other notable ICs inside the D11-100 include a Broadcom BCM3430 CMOS tuner, the source of the transport streams that the BCM7312 subsequently decodes, and an STMicroelectronics LNBH21 LNB (low-noise-blocker) power supply and control chip.

As is typical with systems intended for high-volume, consumer-electronics applications, the digital portions of the design consume a notably small percentage of the overall board area, thanks to Moore's Law. Discrete transistors and regulators; passive capacitors, inductors, and resistors (some quite large in size); transformers; and other analog and power components are scattered across the board, so numerous in part because the D11-100 handles AC-to-DC conversion within the enclosure versus in a "wall wart" or other external converter.

The access-card connector is another significant inhabitant on the system board, whose backside (not shown) is predominantly consumed by traces and through-hole solder points, although a few small passive components are also present.

Read more Prying Eyes

Back-panel connections include an RF coax satellite input; dual two-channel audio outputs; and RF coax, S-Video, and dual composite-video outputs. Why are there two sets of audio and composite video outputs? I'm frankly baffled as to why DirecTV shouldered the additional hardware cost burden here (and the user manual and installer guide are of no help). After all, the two output sets are incapable of carrying different channels' information, since there's only one tuner and decoder in the D11-100. Perhaps the redundancy is so that a user can, in parallel, connect a VCR (for recording) and TV (for display), although there are other and simpler ways of accomplishing this same objective. Or perhaps it's so that two TVs in two (nearby) rooms can both display the same channel content coming from the D11-100.

The D11-100 also offers the ability to tune in an OTA (over-the-air) NTSC broadcast or other UHF-or-VHF-packaged analog video source. A Samsung RMVC10005AE "can" tuner (also stamped BEC1403B) handles this function, along with the broadcast of outgoing RF video on user-selectable VHF channel 3 or 4. The Samsung device is on a daughtercard, suggesting that lower-cost proliferations of the base hardware design might not include one or both features (the RF video input is likely what gets dropped first).

Also on a separate daughtercard is the analog-modem hardware, which probably interacts with soft-modem functionality built into the BCM7312. The analog modem is the means by which the D11-100 periodically "dials home" to download program guide information, firmware, and other updates. That these data streams still come in over POTS is a quaint antiquity in an increasingly broadband-connected LAN and WAN world.

Other back-panel connections include the 27W AC input and a USB port, the latter intended for various remote-control functions. Recent firmware updates have bedeviled traditional COM-to-USB port adapters and their companion software, but clever accessories resurrect other devices' abilities to switch the D11-100 on and change its channel.

Turning your attention to the front of the unit, you'll encounter modularity here as well, likely intended to allow a common base hardware design to serve multiple markets' varying cosmetic tastes. Particularly notice, on the right side of this picture, the IR receiver and, on the left, the clever "light pipe" (also visible in the lower left corner of this picture) that routes the "power on" illumination from an LED on the system board to the front panel.

Author information

Senior Technical Editor Brian Dipert covers mass storage, multimedia, PCs, and peripherals. Contact him at bdipert@edn.com or check out his blog, Brian's Brain.

Editor's note

The above is an extended version of an article that appeared in the print edition of EDN. This PDF file shows the print edition of the article.