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- What:
- The Class A bias current level at which a transistor is operated (Class A operation is where the bias current does not change with RF drive). Bipolars specify the collector current, Ic. FETs specify the drain current, Id.
- Bias current must be adjusted appropriately for expected device performance. Most transistor data sheets contain information at both a noise bias (low current, best noise figure performance) and a power bias (high current, best P1dB). Noise figure has an optimum current, both above and below which performance rolls off. Power generally increases with the square of the current (the exception is when the device is voltage-swing limited). Gain also generally increases with current (implying a device can be used to higher frequencies when biased harder).
- Power devices change bias with drive. Many are specified with a quiescent current (Icq for bipolars, Idq for FETs), the bias current before RF is applied. (This kind of operation is called AB bias).
- Direction:
- needs to fit application
- Range:
- <1 to 500 mA
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