High Efficiency Broadband Doherty RF Amplifier Based On GaN Device

As the communications technology is developing fast,at present,it is in the transition period from 4G communication to 5G communication.Against the background of the rapid rise of 5G communication technology,communication systems are required to have higher throughput,low latency,high reliability,enhanced scalability and energy saving.New technologies require the use of the smallest spectrum to transmit the largest amount of data.Spectrum is expensive,which requires complex modulation techniques to produce wide dynamic signals requiring linear amplification.in addition,energy saving inevitably requires higher efficiency.Therefore,for modern wireless communication systems,power amplifier is urgently required to have high efficiency,wide bandwidth,high linearity,high power and other performance.In order to meet the complex requirements of power amplifier for 5G communication technology applications,a high efficiency and wide band Doherty power amplifier is designed for self-developed devices.The contents and innovations of this paper are as follows:(1)In this paper,an asymmetric broadband Doherty power amplifier based on GaN device is designed.Its carrier power amplifier works in Class AB state.Its drain is powered by 28 V and the gate is powered by-2.7V.The peaking power amplifier works in Class C state.Its drain is powered by 32 V and the gate voltage is-5.2V.Therefore,it has wider power back-off performance.(2)A new input-output broadband matching method is proposed innovatively in this paper.The matching design of input circuit of carrier amplifier and peak amplifier adopts broadband matching of low-pass filter,and the matching design of output circuit adopts the combination of band-pass filter matching and double impedance matching.In this way,not only a wider bandwidth can be achieved,but also the input and output harmonics can be well suppressed.(3)In this paper,a new post-matching circuit design method based on short-section rheostat is proposed,which solves the bandwidth limitation of a quarter-wavelength transmission line impedance converter for Doherty amplifier.The short section rheostat consists of a microstrip transmission line of one sixteenth wavelength,which not only not only can the real impedance transform be realized,but also has the characteristics of filter.In other words,it not only realizes the broadband,but also has a higher degree of out-of-band attenuation jitter than the binomial multi-section impedance converter and Chebyshev multi-section impedance converter,and has obvious suppression effect on out-band clutter.(4)The experimental results show that the Doherty power amplifier based on GaN device designed in this paper not only achieves a saturated output power of more than 44.7 dBm and a saturated efficiency of more than 61%,but also achieves an efficiency of more than 42% when the saturated output power backs off 7dB,in the frequency range of 3.2 GHz~3.8 GHz.In addition,under the condition of 20MHz-LTE test,the ACPR(Adjacent Channel Power Ratio,ACPR)calibrated by DPD(Digital Predistortion)reaches-52.2dBc.