Taming The Wild Powerline

The HomePlug Powerline Alliance (www.homeplug.com) was formed to create an industry standard for high-speed home networking via power lines. Analog Devices' Curt Wise anticipates that HomePlug AV, a 100-Mbit/s version of the spec, will be agreed upon this year.

For LANs, a house's electrical wiring holds advantages over wireless in terms of range. But as a transmission medium, it leaves something to be desired. Because most CMOS DACs provide a current output, an erratic Z0 can produce wild voltage swings on the converter's output pins.

To supply outputs that could be used both in well-behaved wireline applications and in powerline LANs, Analog Devices' AD9865 (see the figure) produces differential current outputs (upper right in the block diagram). They can be steered either directly to an external load or to an internal low-distortion current amplifier. For constant loads, the current amplifier (IAMP) can be configured as a current-mode line driver. For powerline, it can be configured in voltage mode (with two external npn transistors), which can deliver in excess of 23-dBm peak signal power.