A High dynamic range SiGe HBT variable gain amplifier for WCDMA applications
A high dynamic range linear-in-dB variable gain amplifier (VGA) using SiGe HBT devices for WCDMA applications is presented in this paper. The gain is achieved through four stages of amplifiers. The first, third and the fourth stage is the normal amplify stage, and the second stage is the gain control stage. The gain control is implemented by adjusting the bias of the second amplifier. The VGA is driven by a 2.7-V power supply, and has a 49 dB linear gain control range varying from 11 dB to 60 dB when control voltage varies from 0 to 2.7 V. The maximum gain is 60 dB at the frequency of 1.95 GHz, the noise figure is 4.685 dB at maximum gain, input/output VSWRs keep low and constant. The VGA is fabricated in a 0.35 mum fT = 43 GHz silicon germanium heterojunction technology.