Linearity optimizing on HBT power amplifier design

Highly linearized of HBT power amplifier (PA) was achieved for wireless digital mobile communication systems. This study investigates in detail the improvement of the linearity of HBT power amplifiers. The dependence of collector-base capacitance (C"b"c) on bias is regarded initially as a trade-off between linearity and breakdown voltage. A simulation of device performed using SILVACO software reveals that at a capacitance ratio; C"b"c (0/6V) is 1.25 at a BV"c"e"o of 22V. The device-level DC characteristic, load-pull power performance and power cell PAs are evaluated. A reasonably high PAE ~55% is attainable at 2.0GHz and an adjacent channel leakage power ratio (ACPR) of over -48dBc is achieved. The maximum achievable PAE is 54% with a maximum power density of 0.75W/mm at 5.8GHz. The novel HBT epitaxial structure, the layout of power cell design and the thick metal shunt process used to ensure the high linearity of the power cell are demonstrated.