Electronic Design

A Power Supply Must Be Treated As Part Of A Broadband Solution

The variety of broadband communications delivery standards, like G.DMT, G.lite, VDSL, IDSL, voice-over Ethernet, VoIP, derived voice, and so on, continues to proliferate, and these are just the beginning of a long and growing list. While existing standards are well defined, no one really knows what the requirements will be for emerging communications standards.

One thing is certain, though. Requirements will vary considerably from one network implementation to the next, not only in the mix of delivery mechanisms, but also in network scale, topology, and configuration. These variables complicate the design of broadband communications equipment, especially in the area of power supplies. Networking OEMs can implement a variety of standards, present and future, on reprogrammable platforms using DSPs. But the power demands of individual designs are unique, requiring that power-supply solutions be optimized to suit individual applications.

In an industry where performance, cost, and time-to-market are critical, it's essential that power subsystem designs receive equal priority as other subsystems. But the design of broadband communications signal-processing and power-supply functions requires different levels of expertise, something not easily found in one company. So, an OEM must often rely on several IC vendors to match power solutions with broadband communications applications.

Power must be an integral part of a design from the very beginning, because the power requirements of most systems differ. Every system type must balance the cost, size, and efficiency of its power supply differently. For systems that may be used in a large number of network topologies and configurations, determining these tradeoffs can be extremely difficult.

In the central office (CO), for example, traditional analog telephone cards that consume 1 W/line are being replaced by 2-W/line digital subscriber-line (DSL) cards. This dissipation increase leaves no room for inefficiency. Unused power raises operating costs, generates heat, and limits how many lines can be packed into a given space. These same considerations apply to DSL access multiplexers (DSLAMs) in office buildings and residential neighborhoods too. But here, the scale and cost factors differ from those of CO equipment, making for dissimilar optimal power solutions.

Smaller customer premise equipment, such as DSL modems, are less demanding in space with only a single line, or at most a few lines, in use. But cost is a major factor for residential and small-business customers, so power-supply solutions must be as inexpensive as possible. New equipment forms like DSL modems, powered through the Universal Serial Bus (USB), come with slightly different constraints. With a rating of just 2.25 W, the USB supplies only a little more power than the nearly 2 W required by the modem, so there's a distinct need for operating efficiency. Still, other requirements will surface with the emergence of set-top boxes.

A single DSL chip set may serve as the engine for a variety of broadband applications, with different numbers of channels and delivery mechanisms. However, the power demands will vary for each of these systems. Developers have to understand the power constraints of different systems.

Using an IC vendor with the right combination of power-supply and broadband communications products can save OEMs a tremendous amount of development time and speed up the time-to-market. By using optimized power solutions ahead of time, OEMs are able to concentrate on areas where they can apply their expertise and get the greatest return on their investment.

TAGS: Digital ICs
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