A SiGe HBT low noise variable gain amplifier with controllable feedback of a p-i-n diode

A low noise amplifier with dB-linear variable gain has been designed and fabricated based on high performance SiGe HBT in this paper. Negative feedback technology has been adopted to change the transmission gain of HBT through variable resistance of a forward biased p-i-n diode in the feedback path. The simulation results and measurement results agree well in frequency of 1.8GHz for CDMA application. A dynamic gain control of 14 dB in a control voltage range of 0.6–3.0 V has been achieved through the controllable feedback of the p-i-n diode. The noise figure was always lower than 5.5dB when the controlled voltage changed and the minimum noise figure is about 2.6dB. Both input matching and output matching maintained constants under all controlled voltage points.