Adaptive Feedforward Amplifier Design

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2005Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2005Bu çalışmada, özünde doğrusal olmayan bir güç kuvvetlendiricisi uyarlanır ileri besleme yöntemi kullanılarak doğrusal hale getirilmiştir. Temel ileri beslemeli bir kuvvetlendirici iki adet döngüye sahiptir ve iki adet kuvvetlendirici kullanır. Birinci döngünün çıkışında güç kuvvetlendiricisinin (asıl kuvvetlendirici) neden olduğu hata işareti (iç-modülasyon bozulması) elde edilir. İkinci döngüde ise elde edilen bu hata işareti kullanılarak kuvvetlendirici çıkışında oluşan bozulma işareti yok edilir ve böylece kuvvetlendirici doğrusallaştırılmış olur. İleri besleme duyarlılığı çok yüksek olan bir yöntemdir. Bu nedenle her iki döngüde de birer uyarlanır denetim devresi kullanmak gereklidir. Bu denetim devresi her iki döngüdeki alt ve üst yollar arasındaki genlik ve faz dengesini kontrol altında tutmak ve her zaman için dengede kalmasını sağlamak için kullanılır. Sayısal işaret işleme (DSP) tabanlı kontrol devresi en küçük karesel ortalama (LMS) algoritmasını kullanarak uyarlama katsayılarını hesaplamaktadır. Her iki döngüdeki genlik ve faz ayarı vektör modülatörleri kullanarak yapılmıştır. Sonuç olarak, 5.8GHz uyarlanır ileri beslemeli kuvvetlendiricinin benzetimi yapılmıştır ve benzetim sonucunda kuvvetlendiricinin iç-modülasyon performansının 25dB iyileştirildiği gözlenmiştir.In this study, an inherently nonlinear power amplifier is linearized by using feedforward technique. A fundamental feedforward amplifier has two loops and uses two amplifiers. Error signal (intermodulation distortion) caused by power amplifier (main amplifier) is obtained at the output of the first loop. In the second loop, distortion signal at the output of the amplifier is cancelled by using this obtained error signal and thus amplifier is linearized. Feedforward is a method, which has a very high sensitivity. Hence, it is necessary to use adaptive control circuit in each loop. This control circuit is used to check on amplitude and phase balances between upper and lower branches of both loops and to guarantee that these balances is always provided. Digital Signal Processing (DSP) based control circuit calculates adaptation coefficients by using Least Mean Square (LMS) algorithm. Gain and phase adjustment is done by using vector modulators in both loops. Consequently, a 5.8GHz adaptive feedforward amplifier is simulated and as a result of simulation, it is observed that intermodulation performance of amplifier is improved by 25dB.Yüksek LisansM.Sc

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