Impact of Large-signal Operation on DC Operating Point of Horizontal Current Bipolar Transistor

The impact of bias configuration on DC operating point in large-signal operation is analyzed for Horizontal Current Bipolar Transistor (HCBT) by time-domain load-pull measurements at 2.4 GHz. The two limiting cases, constant base-emitter voltage (c-VBE) and constant base current (c-IB), are investigated with respect to where the hard-limitation occurs, in the cut-off or saturation region. For the two cases, it is found that the linear operating range, in which the gain is flat, heavily depends on the hard-limitation type present. Additionally, operation above open-base breakdown voltage shows sharp decrease of DC collector current of 23 mA near compression point for c-IB bias. Finally, the c-V BE bias shows around 5% higher collector efficiency in the back-off range while targeting the same output power in I-dB compression point.