Design Of High Efficiency RF Power Amplifier Based On Doherty Structure

Modern mobile communication systems are moving toward high capacity,high data transmission rates,and the like.More complex modulation techniques are used to improve spectrum utilization,signal data transmission rate,and network delay,such as multi-carrier orthogonal frequency division multiplexing modulation.The complex modulation method results in a signal with a high peak-to-average ratio(PAPR),which requires the RF power amplifier to work at a large power back-off point to maintain the linearity of the power amplifier.However,the traditional Class AB high-linear power amplifier has a low efficiency at the back-off point.In the Sub-6GHz frequency band,the power amplifier circuits in the front end of the high-power base station are mostly based on discrete power tubes for circuit design,and the high efficiency architecture such as Doherty is used to solve the problem of low efficiency of the power back-off point,and the linearity is improved by the pre-distortion technique.However,in the single-chip MMIC RF mobile terminal power amplifier,the problem of low efficiency at the power back-off point is still serious due to the consideration of chip area and cost.In order to solve the problem that the single-chip MMIC is too low in power back-off point,this paper has done the following work:1.Research on efficiency improvement theory: The F-type RF power amplifier output matching structure is deduced in detail,and a simplified matching circuit structure of harmonic impedance control is designed.A detailed study deduces the wor king principle of the Doherty structure and outputs the type of architecture that matches the synthetic network.An output matching circuit for miniaturizing the on-chip Doherty structure is designed.2.Research on sub-circuit function module: Research and design of temperature compensation bias circuit.In the temperature range of-40 ° C to 85 ° C,the bias circuit has a compensation effect on the quiescent current of the RF transistor,and the quiescent current fluctuation amplitude is small.Based on the research of on-chip power detection circuit,a power detection circuit with temperature compensation that is easy to implement on-chip is designed.In the research on the miniaturization of Doherty structure,the replacement relationship between LC miniaturized network and ?/4 wavelength transmission line is studied;the LC phase shifting network which is easy to implement on chip is studied.3.Using the HBT process,a high linearity and high efficiency RF power amplifier with temperature compensation was successfully designed by using the harmonic control matching circuit structure.It can be applied to the micro base station,working in the Band3 downlink,output saturation power 33 dBm,power gain 35 dB,small signal bandwidth,1600MHz-2000 MHz,under the LTE-TM1.1(10MHz)signal test condition,the average output power is at 24.5 dBm,ACPR =-46 dBc and efficiency is 14%.4.Using the HBT process,a Doherty high-efficiency RF power amplifier working in the Band3 is designed.The output matching power synthesis circuit and the harmonic control type power synthesis matching circuit are studied in detail,which further improves the output efficiency of the power amplifier.The simulation results in ADS show that the output saturation power is 33 dBm,the power gain is 33 dB,and t he small signal bandwidth is 1600MHz-2000 MHz.When the average output power is 24.5dBm,the two-tone third-order intermodulation IMD3=-40 dB,using 64 QAM signal simulation: ACPR=-41 dBc,efficiency 31%.