Browsing by Subject "Power amplifiers."

Now showing 1 - 3 of 3

Open Access
Adaptive digital predistortion for linearization of power amplifier
(2009) Şekerlisoy, Burak
In most communication systems, power amplifiers are used to obtain high output power. The nonlinear characteristics of the power amplifier leads to the distortion of the output signal. This distortion affects the efficiency of the power amplifier. The way to reduce this effect is to linearize the power amplifier near the saturation region where it is nonlinear. The widely used technique for the linearization of power amplifiers is predistortion. The proposed technique for predistortion uses a LUT(look-up-table), a complex multiplier, an address calculator, delay elements and an adaptation logic. A new adaptation logic to update the LUT coefficients, is used. The predistorter is simulated in Matlab software using a baseband model for the power amplifier. 16-QAM baseband modulation is used to simulate the predistorter. In order to see the performance of the proposed predistorter, hardware logic is implemented in FPGA and experimental setup with RF circuits and RF power amplifier is used. For different LUT sizes, the algorithm is tested and for the LUT size of 64, nearly 15 dB improvement in power spectrum is observed. The LUT size of 64 is observed to be the optimal LUT size in the experiments.
Open Access
Adaptive digital predistortion for power amplifier linearization
(2008) Aslan, Makbule Pehlivan
High power amplification of linear modulation schemes which exhibit fluctuating envelopes, invariably leads to the generation of distortion and intermodulation products. In order to avoid these effects, maintaining both power and spectral efficiency, it is necessary to use linearization techniques. By using linearization techniques, the amplifier can be operated near the saturation with good efficiency and linearity. The technique proposed here is predistortion based on a look-up table (LUT) method using input and output signal envelopes. The predistortion is implemented using a LUT and an address generation block that selects the appropriate coefficient from the LUT, given the magnitude of the input signal. The testing of the predistorter is done by using a baseband system model which consists of a 16-QAM modulator, an upsampler, a raised cosine filter, the predistorter and a baseband behavioural amplifier model. The performance of the predistorter with a new LUT update method is evaluated in terms of power efficiency and spectrum efficiency. MATLAB simulations show that to obtain up to 25-30 dB improvement in power spectrum is possible and sufficiently large LUT size is needed to reduce the background noise level. Furthermore, the performance of the predistorter in the case of an amplifier with memory is also investigated. The algorithms have been implemented on an FPGA chip. The performance of the system is as predicted in MATLAB simulations.
Open Access
A ku-band phemt mmic high power amplifier design
(2014) Değirmenci, Ahmet
Power amplifiers are regarded as the one of the most important part of the radar and communication systems. In order to satisfy the system specifications, the power amplifiers must provide high output power and high efficiency at the same time. AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMT) provides significant advantages offering high output power and high gain at RF and microwave frequencies. Considering the electrical performance, cost and the reliability issues, pHEMT monolithic microwave integrated circuit (MMIC) high power amplifiers are one of the best alternatives at Ku-band frequencies (12-18 GHz portion of the electromagnetic spectrum in the microwave range of frequencies). In this thesis, a three-stage AlGaAs/InGaAs/GaAs pHEMT MMIC high power amplifier is developed which operates between 16-17.5 GHz. Based on 0.25 µm gate-length pHEMT process, the MMIC is fabricated on 4-mil thick wafer with the size of 5.5 x 5.7 mm2 . Under 8V drain voltage operation, 26.5-24 dB small signal gain, 10-W (40 dBm) continuous-wave mode output power at 3 dB compression with %25-30 drain efficiency is achieved when the base temperature is 85◦C.