The Research And Design Of A High Efficient Dual-Frequency Doherty Power Amplifier

With the rapid development of communications industry nowadays,various signal transmission mechanism and communications standard have been springing up.However,at the same time,more and more situations of networks coexisting have put forward higher requirements on multi-frequency communication systems.In today's life,as 3G,4G even 5G communication have been deep into our life,multi-frequency communications have become the focus of the current research.And due to the shortage of spectrum resources,people demand higher utilization of spectrum resources.So OFDM and M-QAM are widely used,where signal amplitude fluctuations are large and peak to average ratios are high,to improve the spectrum utilization.However,traditional power amplifier decreases power efficiency significantly when output power is back-off,which deviate to the green energy theory in the nowadays.In order to improve the efficiency at output power back-off and to make more full use of frequency,based on Doherty technology,this paper designs and implements two Doherty power amplifiers,whose main work includes the following three parts:(1)Analyze the traditional technical principles of Doherty power amplifier,design and implement a Doherty amplifier which have 200 MHz working bands and whose center frequency at 2.2GHz.By studying the design of Doherty amplifier from the most basic level,to lay the foundation for follow-up design.(2)When design the dual-frequency Doherty amplifier,the dual-frequency matching network and dual-frequency offset line always become too complex.In order to solve this problem,design a network which can realize four impedance matching.By calculating the S parameter and phase in two frequencies,we design a four impedance matching network which replace traditional dual-frequency output match network and dual-frequency offset line.While this network simplifies the the structure,it also make output power efficiency get more better at output power back-off in two frequencies.(3)According to the above four impedance matching network and dual-frequency Doherty power amplifier theories,design and implement a high efficiency Doherty power amplifier of working frequencies of 0.90 GHz and 2.3GHz.Its maximum output powers were respectively 44.2dBm and 44.3dBm,and has the efficiency of 59.9% and 50.7% when the output power is 6dB back off,62% and 63% when the output power is saturated.