Monolithic SiGe HBT Feedforward Variable Gain Amplifiers for 5 GHz Applications

Monolithic SiGe heterojunction bipolar transistor (HBT) variable gain amplifiers (VGAs) with a feedforward configuration have been newly developed for 5 GHz applications. Two types of the feedforward VGAs have been made: one using a coupled‐emitter resistor and the other using an HBT‐based current source. At 5.2 GHz, both of the VGAs achieve a dynamic gain‐control range of 23 dB with a control‐voltage range from 0.4 to 2.6 V. The gain‐tuning sensitivity is 90 mV/dB. At V_CTRL= 2.4 V, the 1 dB compression output power, P_1‐dB, and dc bias current are 0 dBm and 59 mA in a VGA with an emitter resistor and ‐1.8 dBm and 71mA in a VGA with a constant current source, respectively.