Study And Design On Power Amplifier With Proportional Series Combining Transformer

With the rapid development of mobile telecommunication,portable devices need better performances on data rate,the communication distance and battery life,which brings ever increasing challenges for power transmitting.As the key circuit of radio frequency front-end,the radio frequency power amplifier（PA）should satisfy the requirements of output power,efficiency and linearity for the radio frequency link.Power combining methods have always been most common choices for output power and average efficiency improvements,which demonstrate favorable thermal dissipation and high reliability.However,the low breakdown voltage,increasing parasitic loss and descending power capacity bring more challenges along with CMOS scaling.Therefore,it’s quite meaningful to deeply study the technique of power combining and optimizing the design for radio power amplifier.In this thesis,a novel proportional power combining structure is proposed with the combiner realized by on-chip proportional series combining transformer（P-SCT）.With power mode control,the output power range adjustment range is further extended and the back-off efficiency is significantly improved comparing with conventional symmetric combining method.Meanwhile,the proportionality coefficient m could be adjusted if needed,which brings more room for power combining design.As the proof-of-concept,single-die PA solutions are developed with proposed proportional power combining structure.Three kinds of PA with P-SCT were implemented in standard 0.18μm CMOS technology.The main work are as follows:A dual-channel PA adopts proposed P-SCT with wide output power adjustment range is developed,which consists of balun,driver stage,power stage,dual-channel P-SCT and inter-stage.A novel inter-matching network adopting tunable capacitors is proposed,which makes good use of output power of driver stage and prevents inter-matching loss in different power modes,therefore the power gain,output power and efficiency can be acquired.The chip can be applied in 2.3².4 GHz LTE and WLAN applications,the measurement results showed that,with the input of 2.4 GHz carrier wave signal,the PA could achieved a maximum linear output power(P_1-dB)of 18.6 dBm,23.5 dBm and 26.8 dBm in low,medium and high power modes,with the power-added efficiency（PAE）of 16.8%,25%and 31%,respectively.With power mode control,the high efficiency range exceeded 8.2 dB,more than60%wider than conventional symmetric combining structure.The result of error vector magnitude（EVM）demonstrated that the proposed design could meet the requirements of LTE2.3 GHz 20 MHz/64-QAM signal and WLAN802.11g signal,respectively.A folded power combiner structure cooperating with proportional series transformer topology is developed.Power delivery efficiencies are improved due to the inherent cross-coupling coefficients of proposed folded proportional series combining transformer（Folded P-SCT）,lower parasitic resistance of secondary coil winding comparing with unfolded transformer.An accurate estimating method of power delivery efficiency is developed,the simulated results show that,the power delivery efficiency is improved by over30%in lower power mode.Measurement results showed that the designed PA could achieve a maximum linear output power(P_1-dB)of 19.8 dBm,23.9 dBm and 27.2 dBm in low,medium and high power modes,with the power-added efficiency（PAE）of 24.1%,28.1%and 31.6%,respectively.The back-off peak efficiency especially in low mode,was improved by 7.6%compared with unfolded combining transformer.In order to realize adaptive power mode control,the combining power amplifier should satisfy the essential requirements of low gain differences and low phase variations in different power modes.Therefore,a novel on-off channels controlling power divider with phase compensation network is proposed,the proposed design exhibits good channel isolation and low insertion loss in different power modes,meanwhile good phase synchronization can be guaranteed by compensation network.Based on the proposed design,a single-stage dual-channel power amplifier is developed,which consists of switching controlled power divider,power stage,folded P-SCT stage,adaptive power mode controlling logic and the Measured results show that,the PA can achieve a P_1-dB of 27.0 dBm with PAE of 30.5%,power gain of 9.5 dB at back-off region with dynamic range of 0.7 dB.The measured results demonstrated that the power gain is flat and PAE is favorable due to low and stable insertion loss characteristics of switchable power divider.In conclusion,the developed proportional combining method demonstrates a wider output power adjustment range and a better back-off efficiency comparing with conventional symmetric combing structure.The study results achievements of this thesis can be applied to the 4G mobile power transmitting or WLAN signal amplification,furthermore as a reference for the 5G mobile power transmitting applications in low frequency band.