The experimental design and characterisation of Doherty power amplifiers

[摘要] Modern day digital modulation techniques in communication systems produce large peak-to-averageratios. To maintain linearity, power amplifiers have to operate at backed-off levels. This results in lowefficiency with consequences such as high power consumption, short battery life and excessive heatin power amplifiers. A Doherty amplifier is an efficiency enhancement technique which increases anamplifier's efficiency at backed-off levels.This thesis presents a design procedure for a Classical Doherty amplifier. A method where Sparametermeasurements from a transistor are used to predict the transistor's transmission phaseresponse for varying input power is presented. This method is found to be accurate by comparing itto measurements done on a non-linear network analyser. The measured S-parameters are alsoused to design the Doherty amplifier at its predicted peak output power.Two Classical Doherty amplifiers are designed, manufactured and characterised. Themeasurements are performed on a custom measurement setup using in-house developed Matlabcode to automate the measurements. The first Doherty amplifier used small-signal Siemens CFY30GaAs FETs and the second Doherty amplifier used 10W Motorola MRF282 LDMOS transistors. Theperformance of both amplifiers is compared to similar balanced amplifiers and shows improvementsin their efficiency.The improvement in efficiency for the 10W Doherty power amplifier in relation to a balanced amplifieris compared to results found in the literature and a good correspondence between the measuredand published results were obtained.

[发布机构] Stellenbosch University