Bias voltage versus supply voltage

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This is a commonly misunderstood topic, and we're here to help.  Most authors and presenters get this wrong, but after read this page and know the problem you can act as official agents of Microwaves101 and correct all your colleagues. Below we re-post the content of an email from Chris which explains all.

Gates are "biased", as are grids and bases, but plates, collectors and drains are supplied with voltage. I think the (miss)use of the word "bias" has been started by non-native English speakers, who has no conception of the English word "bias". As we all know setting the quiescent current in an amplifying device (Idq for a FET) is set by the normal, no-signal, voltage (or current) of the control element ( grid, gate, base etc). If we set zero current through the main current path, varying the voltage on the drain, or plate etc, will not change that current, unless you send it into breakdown, which would be a dumb idea. Thus the plate, drain etc. cannot be responsible for the device quiescent current, and cannot be called a "bias" terminal. For the drain terminal, "bias voltage" should perhaps be substituted with the words "supply voltage " or just "voltage"."Drain bias" is a misnomer, and should be avoided as much as "tech", as it is factually incorrect.


Now then, repeat after us:

Drain supply, or drain voltage, or drain supply voltage

Gate bias, or gate bias voltage



Author : Unknown Editor