Push-pull circuits using n-p-n and p-n-p InP-based HBT's for power amplification

P-n-p heterojunction bipolar transistors (HBT's) have been combined with n- p-n HBT's in a push-pull amplifier in order to obtain improved linearity ch aracteristics. Simulations of common-collector push-pull amplifiers demonst rate an improvement of 14 dB in second harmonic content at the onset of pow er saturation under Class-B operation. Further improvement of 14 dB in the third harmonic content is shown by moving to Class-AB operation at an expen se of 4% decreased efficiency. A common-emitter push-pull amplifier was fab ricated using both n-p-n and p-n-p HBT's with external matching and coupler s; Testing of the circuit under Class-AB conditions showed better third-ord er intermodulation (by similar to 9 dBc) and smaller second harmonic conten t (by similar to 11 dBc) compared with n-p-n HBT's alone. While the second harmonics were shown to combine destructively in the push-pull amplifier, t otal cancellation of the second harmonic was prevented by the wide differen ce in linearity characteristics of the n-p-n and p-n-p HBT's. In addition, the circuit produced over 2 dBm more output power than the n-p-n HBT alone at 1 dB of gain compression.