| 摘要 |
A bias circuit for a radio frequency linear power amplifier having an input for selecting one of a plurality of operating modes varying in quiescent current of an bipolar transistor, a thermally responsive element for sensing a temperature, a circuit for biasing the output bipolar transistor, receiving said selecting input and incorporating said thermally responsive element, for maintaining linear performance in each of said modes over a range of temperatures, and a filter 6, 41, 42, 43 for attenuating noise generated within the linear power amplifier. The use of a tank circuit at the collector of a power radio frequency transistor, having an inductor capable of handling the collector current, resonating with a capacitor at the design frequency, permits a reduction in the required inductance and therefore higher levels of integration. The tank circuit, including the self-inductance of the capacitor, is preferably designed to also resonate at the second harmonic of the design frequency, to provide improved linearity. The bias circuit may be bandwidth limited, to reduce noise and improve phase margin. Improved bias circuits increase efficiency for operating a radio frequency power amplifier in a linear operation range, with respect to changes in temperature Hfe and voltage, while maintaining low quiescent current. The bias circuits also maintain low noise levels. |
