The Toshiba PCX2600 Cable Modem highlights the commoditizing pattern in the cable business. Driven by the industry-standard DOCSIS data-over-cable specification and enabled somewhat misnamed single-chip IC solutions, the modem has shed its carrier-class equipment heritage entered the realm of electronics superstore gadgetry. burgeoning appetite for high-speed data to the home driving changes in the modem industry. While consumer broadband is still in the relatively early phase of market share of cable-based delivery is claimed lead over the primary competition from DSL solutions. Inherently a fat digital pipe to your PC, the cable modem must first deal with the analog realities of RF frequency control, tuning, line filtering, modulation, demodulation, and general power management for the supporting components.
Since inbound and outbound data is carried on bandwidth borrowed from cable television spectrum, the front door to the modem is a tuner"shown here removed from the main board and its shield-can enclosure. The Tuner Module assembly is manufactured by Toshiba and houses a 2-layer phenolic/fiberglass board which makes liberal use of through-hole construction.
Composed largely of discrete coils, capacitors, resistors, and transistors, the assembly also uses two ICs to craft the analog tuner and demodulation. Front-end CATV amplification comes from a Maxim MAX3514 while a silicon tuner, believed to be supplied by Toshiba, provides precise band discrimination to separate out data channels from the TV clutter. The main board is a 6-layer PCB that supports a digital modem design centered around the Texas Instruments TNETC4401 PYP Broadband Network Controller, a part compatible with the most current DOCSIS 2.0 standard. An Ethernet controller from Realtek (#RTL8201B) serves as the interface to the host PC or router. Flash and SRAM"for code and working memories"are supplied by ST Microelectronics and Hynix respectively. Power-management devices from AnaChip provide both PWM supply control and onboard regulation.
Mechanical construction of the modem is straight forward, consisting of a two-piece ABS plastic enclosure with a plated-steel RF shield liner to keep interference at bay. Estimated cost-of-goods-sold (COGS) for the PCX2600 is less than half the $80 retail price, reflecting the competitive nature"and modest margins"of the cable modem product space. While much of the COGS is driven by main board chip content, analog related components carry a meaningful part of the value chain and provide an essential piece in the product design.
David Carey is President of Portelligent. The Austin, Texas company produces teardown reports and related industry research on Wireless, Mobile, and Personal Electronics. (www.teardown.com)