Research On RF Power Amplifiers For Wireless Communication Networks

Power Amplifiers and Low Noise Amplifiers are ones of the most important components in any wireless communication system.Most of the wireless communication signals suffer from high peak-to-average ratio,which in turns reduces the efficiency of the power amplifier at the back-off power levels.This will result in energy wastage and affect the device reliability and performance,thus effecting the indexes like output power,efficiency,bandwidth and linearity.RF Power amplifiers are mostly made in Common source configuration thus offering nonlinearity and a significant power gain.The amplifier is operated in back-off by using digital predistortion technique which is used to improve linearity.On the other hand by using common drain configuration,linearity and efficiency can be achieved.In practical application,Low Noise Amplifier and the Power Amplifier are usually used in communication system,but both of them have a slightly different roles,such as priorities,working condition and parameter regulation regarding their performances.The LNA functions at the front end of the receiver channel by capturing and amplify the low power signals with added noise within the allotted bandwidth.The PA in this contrast,receives and simultaneously amplifies a high SNR signal and its basic job is to boost the signal power and thus face challenges regarding efficiency and gain.In this dissertation,based on the Amplifiers operation principle,key aspects regarding Amplifiers are studied relating to LNA and Power Amplifiers.Three new amplifiers are proposed and designed.The main innovative contributions are listed as follows:1.A new design for wideband LNA is proposed for the wireless applications in the range 0-2.4 GHz.The new LNA design is based on biasing network with common source inductive feedback.The result of using this technique is gain enhancement,Noise Figure reduction and low power consumption.It was also noticed that the input matching network has reduced the noise figure to a level of 0.5 dB and the output matching network has enhanced the gain to more than 17 dB.The proposed amplifier structure showed good stability for the entire range of frequency so no external stabilizing components were used thus simplifying the design and in turn reducing the cost and size of the amplifier.This design was also compared to the other designs which used CMOS and PHEMT and this design showed better results in terms of gain dB and noise figure dB.2.A Class-E amplifier for X-band operation is proposed and designed by using Microstrip lines and MESFETs technology.The device is suitable for next generation communication devices like 3GPP,LTE and WiMax.The design is optimized for 9 GHz frequency of operation.In this design Microstrip lines are used to reduce the size of the amplifier.Load Pull measurements were used to get MESFETs input and output impedances optimum values.For impedance matching network and for linear and nonlinear operations,small signal mathematical model is used for the design.The design has a high gain of about 25.6 dB and the PAE has peaking value of 30%.The values of input and output return losses are about 22 dB which shows the accurately designed impedance matching network.The simulation and the measured results showed that the amplifier as compared to the existing amplifiers showed better results in terms of gain,power output and PAE etc.3.A Novel Two Stage Broadband Doherty Power Amplifier for Wireless Applications is proposed and designed based on driver amplifier.Klopfenstein taper is used here to enhance the bandwidth.The amplifier uses a novel and simple approach to achieve bandwidth enhancement and at the same time uses a driver amplifier.In this amplifier a two stage Doherty amplifier for multimode operation is used in order to increase the gain of the amplifier without sacrificing much of bandwidth.The proposed Doherty Power amplifier is able to deliver drain efficiency of about 31-35%at output power backoff of 6 dB,while achieving drain efficiency at saturation which is about 40-45%for 1.5 GHz to 2.6 GHz of designed bandwidth.The amplifier can deliver above 3 dBm of output power with the gain of about 20 dB.Here Klopfenstein taper is used in order to get wide bandwidth of more than 1 GHz.The simulated and measured results showed that the proposed amplifier gives better performance as compared to the existing amplifiers in terms of gain,drain efficiency and bandwidth etc.