Magisterska naloga predstavlja načrtovanje in izvedbo visoko kvalitetnega avdio ojačevalnika. Motivacija za izdelavo le tega izvira iz želje po predvajanju kvalitetne glasbe in izdelavi cenovno ugodnega visokokvalitetnega ojačevalnika.
Predstavljen je ojačevalnik, ki ima popačenje pod −80 dB ali 0.01 %. Simulacijski rezultati dokazujejo, da tako majhno popačenje lahko dosežemo le z nekaterimi topologijami ojačevalnikov. Ojačevalnik je namenjen za krmiljenje namiznih zvočnikov, ki zahtevajo nizke moči do 10 W. Pri načrtovanju so bili uporabljeni tranzistorski pari za vhodno ojačevalno stopnjo. Opravljena je bila tudi analiza vpliva različnih topologij izhodne stopnje in načinov dovajanja mirovnega toka.
Meritve kvalitete predstavljenega ojačevalnika so bile narejene z uporabo laboratorijskega avdio spektralnega analizatorja Keysight U8903B. Na podlagi meritev in prilagajanja povratne zanke ojačevalnika je bilo možno doseči −100 dB popačenja na ožjem frekvenčnem področju. To so vrednosti, ki dosegajo meje območja meritev spektralnega analizatorja.
Meritev se je opravila tudi na cenovno ugoden način. Za generacijo sinusnega signala z nizkim popačenjem je bil uporabljen kvaliteten digitalno-analogni pretvornik TI PCM1794 in za zajemanje diktafon Tascam DR-22WL. Posnetek se je analiziral v Matlab okolju z FFT analizo. Rezultati so pokazali popačenja v razredu −90 dB. Razlog za slabše popačenje je bil uporabljen DA pretvornik in ne predstavljen ojačevalnik.
V zaključku so predlagane dodatne izboljšave ojačevalnika in napajalnikov na vezju z meritvijo frekvenčne karakteristike povratne vezave.
| Language: | English |
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| Title: | A low harmonic distortion audio amplifier development : magistrski študijski program druge stopnje Elektrotehnika |
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| Abstract: |
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The master thesis presents a design and execution of a high-quality audio amplifier. Inspiration for choosing this topic comes from passion from listening to high quality music with an innovative design that can be built for an affordable price.
An amplifier with distortion of less than –80 dB or 0.01 % is presented in the thesis. Simulations prove that such low distortion is possible to achieve with only a few amplifier topologies. The amplifier is designed to drive bookshelf speakers, which need low power levels up to 10 W. Transistor pairs were used in the design for an input stage. An analysis of different amplifier topologies and bias methods was also performed. A laboratory audio spectrum analyser Keysight U8903B was used to precisely measure audio distortion of the amplifier. A THDR down to –100 dB was measured in some frequency ranges after component optimisation in a feedback circuit. The amplifier thus nearly reached the THDR of the spectrum analyser.
An affordable method for measuring THDR was also used. A quality digital-to-analog audio converter TI PCM1794 was used to generate reference sine signal for THDR measurement. For amplifier output signal acquisition a handheld recorder Tascam DR-22WL was used. The recording was analysed in a Matlab environment using an FFT function. The spectrum analysis returned THDR around −90 dB. The reason for higher THDR measurement was a DA converter that is not capable of producing sine with specified accuracy (−108 dB).
Additional amplifier and power supply optimisations on the circuit are recommended at the end of the thesis. The improvements can be made by optimising the feedback loop and measuring its frequency response.
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| Keywords: | Precision audio amplifier, THD, Class A-B-AB, Feedback, Altium Designer, LTSpice, MatLAB, Audio spectrum analyser, Transistor pair, Digital to analog converter, Fusion 360 |
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