Browsing by Subject "Power amplifiers--Design and construction."

Now showing 1 - 5 of 5

Open Access
A band selecting UHF class-AB GaN power amplifier with 40 dBm output power
(2013) Alemdar, Sinan
Ultra High Frequency (UHF) band is used for GSM communication, satellite systems, television broadcast, frequency hopping radios, software de ned radios using advanced digital modulations. Each and every application would require various speci cations and these modern applications require various frequency bands. In this work, a band selecting uhf class-ab GaN power ampli er with 40 dBm output power is built using a GaN-HEMT transistors and PIN diodes. The power ampli er can be tuned in 1350MHz{2700MHz one-octave frqeuency band, has a maximum gain of 17dB, and a maximum saturated output power of 41 dBm.
Open Access
Design of a high efficiency power amplifier by using Doherty configuration
(2010) Peker, Kazım
Power amplifiers (PAs) have their highest efficiency when they are used at full power (0dB back-off). For this reason, most PAs are used at 1dB compression point (P1dB), but this point is highly nonlinear. For high linearity, PAs should be used at some back-off value (below the point of 1dB compression point). In this case the efficiency of PAs decreases drastically. Another issue is that widely used digital modulation techniques produce signals which has a large peak-to-average power ratio (PAPR). In modern systems the power is reduced automatically to use spectrum efficiently and to prevent interference and detection. These conditions force new PA designs to have both high linearity and high efficiency from P1dB point down to a few dB back-off region.Doherty Amplifier technique uses Class-AB and Class-C amplifiers in parallel, and an increase in the efficieny especially at back-off regions occurs. By the use of parallel configuration P1dB point is improved. In the thesis, the theory of Doherty Configuration is explained, a Doherty Amplifier working at 4.75GHz is designed and simulated. A balanced amplifier is also designed and the results of both amplifiers are compared. The P1dB points of balanced amplifier and Doherty Amplifier are nearly same. In the Doherty case, a significant increase in efficiency is obtained at 6-dB back-off point and a little increase in efficiency is obtained at P1dB point. A Doherty Amplifier at 2GHz is implemented and its efficiency and linearity is compared with the implemented single amplifier. Significant increases are achieved both at P1dB point and at the efficiency.
Open Access
Design of an S-band power combiner system with two parallel power amplifiers and phase shifters
(2011) Özbey, Burak
RF power amplifiers are important blocks in a wireless communication system that play a vital role in determining the level of overall performance. In some situations, more power than a single power amplifier can alone provide is required in applications such as a radar or a space communication system. In such cases, power combiners that can surpass the maximum output power level of a single power amplifier should be used. In this thesis, we study the performance of a power combiner built in classical binary structure. The combiner operates at 3 GHz (S-band) and comprises two power amplifiers which can supply up to 38 dBm of saturated power. Wilkinson power dividers/combiners are utilized at the input/output respectively in order to divide and combine the input and output signals. While building a power combiner, one should also note that the phases of the amplified signals should be matched at the output or else the level of combining loss can reach significant levels. At a phase difference of 180◦ , the signals will be completely out of phase and will combine destructively at the output. Therefore, in our study, in order to be able to control the phases at each arm of the power combiner, two tunable microwave phase shifters are placed before the active devices. The phase shift generated by these shifters are controlled via voltage, hence a desired level of phase shift can be obtained. By this, we demonstrate that phase shifters are also important structures for a power combiner that are instrumental in accomplishing a phase balance between the two arms. The idea behind the work displayed here can be extended to applications requiring much higher power levels or operating at higher frequencies.
Open Access
Dynamic power supply design for varying envelope signals using envelope tracking method
(2012) Özel, Muhlis Kenan
In modern communication systems, demand for higher data-rate is consistently growing. Higher data-rate within a limited bandwidth tends to require more amplitude modulation (AM) to increase number of symbols per second. Amplitude modulated carriers should be amplified using linear power amplifiers (PAs). Although, linear PAs have good performance in terms of linearity, they are efficient only when they transmit at maximum power. However, modern communication signals have high peak-to-average-power ratio (PAPR), therefore probability of a PA transmitting at maximum power is low. As a conclusion, efficiencies are degraded to alarmingly low values and the problem translates to heat and shorter battery life issues. In this thesis, we investigate how dynamic power supplies (DPS) perform for non-constant envelope RF signals. We have designed a DPS and used it to test efficiency enhancement of two PAs compared to the same PAs operating with constant supply. Our aim was to obtain efficiency increase compared to constant supply case without introducing extra non-linearity. We have obtained satisfying results for both amplifiers.
Open Access
A fully integrated K-Band power amplifier design using digital 018 [formula] CMOS technology
(2011) Kelleci, Ceyhun