| Nowadays, wireless communication has become an essential part of people’s daily life. Power amplifier (PA), which is located at the radio frequency (RF) front end module of wireless communication system, is one of the most power consuming components. The performance of PA directly affects the communication quality and coverage range, and to a large extent determines the total energy consuming. Gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) has been widely used in RF PA for its outstanding features, such as single power supply, high power density, high efficiency and good linearity. This dissertation is focused on the improvement of output power and efficiency for GaAs HBT RF PA.First, the topology of stack transistor structure with high output power and high efficiency PA design technique with harmonic control are investigated. Based on the study above, a design method of harmonic control stack PA technique is proposed. A 2.4GHz-2.7GHz high efficiency and high power stack PA is developed and fabricated. The main work and contributions of this dissertation are as follows:(1) The optimum inter-stack matching condition is hard to reach for traditional stack PA. A new matching method is then proposed, which utilizes a series resistor and capacitor as a shunt connected to the base of upper transistors. This stack structure could get an optimum load for each stack layer, which promises every transistor layer reach the optimum output power feature. This design method effectively increases the power combine efficiency of every layer transistors, and improves efficiency and linearity features of stack PA. The experimental results show that this design method compared with the traditional stack PA design could enhance the PAE by 6% at P1dB output power, and improve the EVM by 1.8 dB at 6 dB back-off output power.(2) As the current mode power amplifier could not get high efficiency, a second harmonic control technique is proposed for common emitter amplifier. It utilizes a nonlinear output capacitor of GaAs HBT to tune the fundamental and second harmonic loads. This technique could improve the output power, decrease the power dissipation, and raise the efficiency of PA. The experimental results show that the new designed PA compared with the design whose output matching is only at fundamental frequency could increase the output power by 1.3 dB, and improve the efficiency of 9.2%.(3) The proposed harmonic control PA technique is adopted to further improve the efficiency of current mode stack PA. This technique uses the nonlinear output capacitor of each stack layer, the paralleled capacitor and the shunt resistor-capacitor connected to the base of upper layer transistors to manipulate the fundamental and second harmonic loads for each layer. It could shape the voltage waveform for every layer, increase every layer transistors’ output power and decrease the total power dissipation. This design method provides the solution of harmonic control technique applied to stack PA. This design technique benefits high feasibility, and is easily transplanted to other HBT process stack PA design.At last, a 2.4GHz-2.7GHz two stage stack PA with second harmonic manipulation technique is implemented using 2 μm GaAs HBT process. The measurement results show the gain is higher than 30 dB from 2.4 GHz to 2.7 GHz under 9 V supply voltage. The output power could reach 34.2 dBm with PAE of 48% at 2.5 GHz. The measurement results are in line with the simulated results, which verify the validity of this design method.
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