Variable gain SiGe HBT amplifier with low noise figure

The advances in SiGe processing technology are increasing the transit frequency f/sub T/ of transistors. In combination with the small base resistance of SiGe devices, low noise transistors are available. This kind of device can be used to design low noise amplifiers in the low GHz range for mobile communication products. Power fluctuations in mobile networks require low noise amplifiers with variable gain. This paper presents a low noise amplifier with variable gain using SiGe technology at f=900 MHz. The gain is V=18.4 dB at f=900 MHz with a noise figure of F/sub 50/=2.2 at 50 Ohm respectively. The attenuation is cascaded in three stages with an attenuation of a=3 dB per stage.