Monolithic SiGe HBT variable gain amplifiers with a feedforward configuration for 5-GHz applications

Monolithic SiGe HBT variable gain amplifiers with a feedforward configuration have been newly developed for 5-GHz applications. For bias-current control, two types of the VGA have been made: one using a coupled-emitter resistor and the other using HBT-based current source. At 5.2 GHz, both of the VGAs achieve a dynamic gain-control range of 23 dB with the control-voltage range from 0.4 to 2.6 V. The gain-tuning sensitivity is 90 mV/dB. The VGAs with an emitter resistor and a current source produce a maximum gain of 8.8 dB and 8.2 dB, respectively. At V/sub CTRL/=2.4 V, an 1-dB compression output power P/sub 1-dB/ and dc bias current are 0 dBm and 59 mA in the VGA with an emitter resistor and -1.8 dBm and 71mA in that with a constant current source, respectively.