Reconfigurable SiGe Low-Noise Amplifiers With Variable Miller Capacitance

A new input matching method making use of shunt-shunt feedback capacitance is introduced. Based on the new input matching method, reconfigurable SiGe low-noise amplifiers (LNAs) by varying shunt-shunt feedback capacitance are proposed. Two approaches are used to vary the shunt-shunt feedback capacitance. One approach is to switch between two different bias currents while the other is to use a series combination of a switch and a capacitor. Miniaturized fully monolithic reconfigurable SiGe LNAs without emitter degenerative inductors were realized by the above two approaches. The reconfigurable SiGe LNA achieved by switching bias currents only occupies a very small area of 355 mumtimes155 mum, excluding measurement pads. This LNA achieves an input return losses (S₁₁) of -27.6 dB, a voltage gain (A _v) of 19.8 dB, and a noise figure (NF) of 3.18 dB for 2.4-GHz band when biased at a current of 3.8 mA and can be reconfigured to obtain A_v=20.4/20.3 dB, S₁₁=-47.1/-24.6 dB and NF=3.42/3.21 dB for 5.2/5.7-GHz band when bias current is switched to 3 mA. In addition, a 2.4/4.9/5.2/5.7-GHz reconfigurable SiGe LNAs for WLAN applications, whose variable shunt-shunt feedback capacitance is controlled by a switch and a capacitor, was also realized