A dual bias-feed circuit design for SiGe HBT low-noise linear amplifier

An SiGe HBT low-noise amplifier (LNA) with a novel diode/resistor dual base bias-feed circuit is described. The dual bias-feed circuit extends P1 dB without degradation of the noise figure (NF). In the small-signal region, a conventional resistor bias-feed circuit is a dominant base current source and, in the large-signal region, the diode turns on and the diode bias-feed circuit supplies the base current like a voltage source, which allows higher output power and linearity. In this paper, the operation principle of the dual bias-feed circuit is explained by using a virtual current source model, which indicates the increase of base current of the HBT in a large-signal region. The design method is also described for the idle current of the diode bias-feed circuit in a small-signal region from the points-of-view of NF and P1 dB. The effectiveness of the dual bias-feed circuit is evaluated by simulation and measurement. The fabricated 2-GHz-band dual bias-feed LNA has the P1 dB improvement of 5 dB and no degradation NF compared with the conventional resistor bias-feed LNA.