A SiGe bipolar-MOSFET cascode power amplifier with improved linearity for low-power broadband wireless applications

In this paper, a novel bipolar-MOSFET (BiFET) cascode differential power amplifier (PA) is proposed and fabricated, showing strong improvement on the linearity performances over those of the conventional bipolar-bipolar cascode PA. The two-stage differential BiFET cascode PA achieves P_out of 25.7 dBm with 52.1 % power-added-efficiency (PAE) in the continuous wave (CW) measurement at 900 MHz. A conventional bipolar-bipolar cascode PA is designed in a similar configuration to compare with the BiFET cascode PA performances, using the LTE 16QAM 5/20 MHz signals as inputs. The measurement results show that the BiFET cascode PA significantly improves the linearity performances over those of the conventional bipolar-bipolar cascode PA in terms of error vector magnitude (EVM), adjacent channel leakage ratio (ACLR) and the transmission output spectra. These linearity improvements are more visible at lower P_out levels, and become particularly striking as the signal bandwidth increases to 20 MHz. The SiGe PAs are designed and fabricated in a 0.35-μm SiGe BiCMOS technology with through-wafer-vias (TWVs) for low-power broadband wireless applications.