A novel SiGe BiCMOS variable-gain active predistorter using current steering topologies

This paper presents the novel design of a 2.4-GHz variable-gain active predistorter (PD) using a 0.35-μm SiGe BiCMOS technology. Current steering topologies are selected for this design to provide dual functions of: (1) an active predistorter for power amplifier linearization; and (2) a variable gain amplifier (VGA) for transmitter power control. Unlike other traditional "passive" predistorters, this active predistorter does not need an additional buffer amplifier to compensate the loss. Furthermore, through the bias voltage control in the low current region, the amount of gain expansion from this predistorter becomes programmable, to compensate for the PA non-linearity. Finally, this variable-gain predistorter could be used as a VGA in a multi-stage power amplifier design and it is well suitable for RF-SOC applications. The PA experimental results of 16-QAM modulated signals show that the compressed constellation can be uniformly spread out into a "square", the spectral re-growth is suppressed by 7-9 dB, and the EVM can be reduced from 9.9 % to 5.7 %.