| In order to meet people’s demand for high-speed and low latency communication,wireless communication technology has undergone rapid development and iteration.As a part of the 5G millimeter wave frequency band,the Ka band has become a research hotspot due to the advantages of low latency and high penetration of signals in this frequency band.RF power amplifier is one of the main components in the transceiver circuit of wireless communication systems.Its amplification ability of signals directly affects the performance of the entire transceiver circuit.However,traditional power amplifiers have a rapid decrease in efficiency when power is reversed,resulting in a significant loss of DC energy.The power amplifier with Doherty structure can still provide high efficiency in the power fallback region by using the Active load traction technology,which has become one of the important research focuses of power amplifier.Based on this background,this article optimizes the input power distribution network and output power synthesis network of the power amplifier,and completes the simulation and design of the Ka band Doherty power amplifier in the 65 nm CMOS process.The main tasks are as follows:Firstly,the paper introduces the structure,basic principles,specifications,and types of power amplifiers,as well as the working principles of Doherty power amplifiers and the active load traction theory.Then it analyzes the parasitic effects of active devices in the circuit and how to reduce the losses of passive devices in the circuit to improve the gain,efficiency,and output power of the power amplifier.Based on the above theory,this paper designs two Ka band power amplifiers based on 65 nm CMOS technology.The first power amplifier uses a two-stage common source differential circuit,and uses cross coupled capacitance technology to neutralize the parasitic capacitance of the transistor gate and drain electrodes.It uses a low loss transformer to match input and output,improving the gain and output power of the circuit.The final simulation results show that at28-32 GHz,the small signal gain is 22 to 24 d B,the maximum output power is 15.8 d Bm,the peak power-added efficiency PAE reaches 25%,and the output power and PAE at the power compression point of 1 d B are 13 d Bm and 16%,respectively.The second Doherty power amplifier is based on the first power amplifier.Both the main power amplifier and the auxiliary power amplifier use a two-stage cascade differential common source circuit.At the input end,a transformer is used to achieve the power distribution of the main and auxiliary power amplifiers and the 90 ° phase difference of the signal.At the output end,a transformer is used to achieve power synthesis and impedance conversion,completing the design of the Doherty power amplifier.The final simulation results show that the small signal gain at28-32 GHz is 20 to 25 d B,the maximum output power is 18.9d Bm,and the peak power-added efficiency PAE reaches 28%.When the power recedes by 6d B,the PAE can reach 20%.The Doherty power amplifier in this article uses a transformer to replace the traditional λ/4transmission lines,solving the traditional λ/4 transmission lines the problem of large area and high loss in the layout,and the Doherty structure is used to improve the efficiency of power amplifier power backoff.Although there are still many shortcomings in the design process,an exploration of Doherty power amplifier design has certain reference value and significance for future researchers in wireless communication systems. |
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