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Active Bias Networks for FETs

Biasing a depletion-mode device (MESFET or HEMT) in a module must be done so that the end-user doesn't have to think about it. The poor man's bias network is a voltage divider using fixed resistor, strapped across a regulated supply such as -5V. One step up from that is using a miniature potentiometer, set with a screwdriver. In both cases you might want to consider creating a network that is only adjustable over a small range, so that it is idiot-proof during adjustment.

Potentiometers may have long-term stability problems and may be susceptible to vibration.

Active bias networks are an elegant, but little understood solution.  For pulsed amplifiers, be sure to think about settling time.

While we wait for content on this page, we'll post some links. Here's someone else's description of an active bias network (it's pretty good), contributed by Fred L,

Also, consider the HBC-1 from Phase IV Components LLC of Huntsville Alabama.

More to come.

 

Author : Unknown Editor

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