Bias
lastmod 2019-10-28created 2015-12-232 edits
In electronics, biasing (Biasing, Q-point) refers to determining the operating point of a voltage or current in advance. It sets up the conditions so that the intended function is performed relative to the operating point. If the intended function can be performed on its own, there would be no need to set the reference point again. It mainly allows a varying signal to adapt to the circuit relative to the reference point.
When building an amplifier with a bipolar junction transistor (BJT) or a field-effect transistor (FET), current flows in only one direction due to the characteristics of the device, so the negative voltage of an AC signal cannot be handled. Therefore, by deliberately adding a DC voltage, amplification becomes possible even with current flowing in only one direction. In this way, it sets up the conditions that allow the input small-signal AC voltage to vary around an arbitrary DC voltage as the reference.