Research Of S-band Doherty Power Amplifier

Power amplifier is one of the important parts of the modern wirelesscommunication system, characteristics of the power amplifier, such as output power,efficiency, linearity and so on, have a great influence on the whole communicationsystem. Especially, most of the wireless communication systems use signals with highpeak-to-average ratio (PAR) which propose higher demands on the output characteristicsof the power amplifier. Consequently, it is significant to do research into the design ofpower amplifier which can be used under the condition of high PAR.This paper aims at the high efficiency Doherty power amplifier working in S band.According to the theory of load modulation and based on the consideration of the kneevoltage effect, the power amplifier with enhanced efficiency was finally realized, themain work and conclusions are as follows:1. Do a further research on the basic theory of high efficiency power amplifier.Focus on the analysis of circuit structure and design procedures of the Doherty poweramplifier.2. Using the Advanced Design System (ADS), a conventional Doherty poweramplifier was realized. Besides, the layout design, physical processing and performancetest were completed. The experimental results show: the1dB compression point outputpower and the average output power are42.5dBm and37dBm. At the two points, theadded efficiency (PAE) reached40%and31%respectively, which meet the designrequirement.3. An improved Doherty power amplifier was designed. Limitations of traditionalstructure efficiency enhancement were anylazed, which include the inaccuratejudgement of the main amplifier saturation point because of the knee voltage effect andthe limitation of the peak ouput power increase due to the unreasonable load modulationin the high input power area. According those cases, the improved scheme was designed,which overcome the decrease of regression brought by the knee voltage effect, inaddition, the load modulation was improved employing the asymmetric structure.Finally, the layout design, physical processing and performance test were realized. The measured results show that the PAE of the improved Doherty power amplifier reached35%at the average output power, which is higher than the conventional one.So thefeasibility of the design and the correctness of the theoretical analysis were verified.`...