Høyerby, Mikkel Christian Kofod

Nærværende afhandling præsenterer et bredt studie af metoder til effektivitetsforøgelse i smalbånds-radio-sendere. Den centrale anvendelse er basestationer til TETRA/TEDS-netværk. I hovedsag studeres løsningsrummet bestående af en lineær klasse-A/B RF-effektforstærker udstyret med en "envelope tracking" spændingsforsyning og linearisering ved hjælp af "cartesian feedback"- teknikken. På systemniveau demonstreres "envelope tracking"-teknikken at være særdeles effektiv i forbindelse med RF-signaler med høj spids/middel-effekt, såsom TEDS med 10dB. Det demonstreres også, hvorledes teknikken kan introducere en række potentielle problemer i form af forsyningsintermodulation (PSIM) og reduceret linearitet i RF-effektforstærkeren. Endvidere understreges indvirkningen af "envelope tracking" spændingsforsyningens udgangsimpedans. Til trods for en høj reguleringsbåndbredde kan denne ikke samtidig kan have en meget lav udgangsimpedans. På blokniveau foreslås og demonstreres løsninger til implementering af "envelope tracking" spændingsforsyninger med fokus på buck-topologier. En række af disse undersøges og sammenlignes med henblik på at illustrere de afvejelser, der skal foretages imellem båndbredde, skiftefrekvens og ripple-spænding. Det vises, at den simple en-fasede buck-topologi med fjerdeorders udgangsfilter er ideel til TETRA – og TEDS -anvendelser. Det overordnede problem bestående i at opnå maksimal reguleringsbåndbredde, givet en bestemt konvertertopologi, behandles dybdegående. En mængde sandsynligvis ny viden på området præsenteres. Det vises, at selvsvingende reguleringsteknikker udgør vejen til den højest mulige reguleringsbåndbredde. Også inkluderet er et studium af de begrænsende faktorer i effektiviteten af "cartesian feedback" (CFB.) Det vises, at reguleringsbåndbredder på over 4MHz kan opnå ved 400MHz bærebølgefrekvens ved brug af lettilgængelige diskrete komponenter. Højere CFB-båndbredde er nøglen til et fleksiblt RF-effektforstærkersystem, der kan transmittere flere bærebølger samtidig. En række kritiske områder i reguleringssystemet identificeres. I praksis demonstreres en høj-effektiv 25W TEDS radiosender, som møder alle nabokanaleffekt (ACPR) – og bredbåndsstøjs (WBN) -specifikationer. Effektforstærkerens virkningsgrad forøges fra 23 % til 44 % - næsten en fordobling - til den beskedne pris af en en-faset buck-konverter og vel at mærke uden væsentlig forringelse af renheden af det afsendte RF-signal.This thesis presents a broad study of methods for increasing the efficiency of narrow-band radio transmitters. The study is centered around the base station application and TETRA/TEDS networks. The general solution space studied is that of envelope tracking applied to linear class-A/B radio frequency power amplifiers (RFPAs) in conjunction with cartesian feedback (CFB) used to linearize the overall transmitter system. On a system level, it is demonstrated how envelope tracking is particularly useful for RF carriers with high peak-to-average power ratios, such as TEDS with 10dB. It is also demonstrated how the envelope tracking technique introduces a number of potential pitfalls to the system, namely in the form of power supply ripple intermodulation (PSIM), reduced RFPA linearity and a higherimpedance supply rail for the RFPA. Design and analysis techniques for these three issues are introduced and demonstrated. On subcomponent level, solutions for implementing the envelope tracking power supply are proposed and demonstrated. A number of buck-type DCDC converter topologies are investigated and compared, with the objective of showing the trade-offs involved between switching frequency, control bandwidth and ripple voltage. It is found that the simple fourth-order filter buck converter is ideal for TETRA and TEDS envelope tracking power supplies. The problem of extracting maximum control bandwidth from a given power topology is given particular attention, with a range of, arguably new, insights resulting. It is clearly shown that single-phase switch-mode control systems based on oscillation (controlled unstable operation) of the whole power train provide the highest possible control bandwidth. A study of the limitations of cartesian feedback is also included. It is shown that bandwidths in excess of 4MHz can be achieved for a 400MHz carrier frequency using readily available discrete components. Even higher CFB bandwidths are the key to flexible RFPA system capable of transmitting multiple RF carriers simultaneously. A number of key problem areas are identified and shown to need further research. Practically demonstrated is a high-efficiency 25W TEDS transmitter capable of meeting all base station adjacent channel power ratio and wideband noise specifications with ample margins. Efficiency is improved from 23% to 44% by application of envelope tracking - almost a doubling - at the cost of a single-phase buck converter and without any penalties in RFPA output spectrum purity

Online Research Database In Technology

High-Performance Control in Radio Frequency Power Amplification Systems

http://orbit.dtu.dk/ws/files/5140448/mwh_thesis.pdf

High-Performance Control in Radio Frequency Power Amplification Systems

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Online Research Database In Technology