Linearized Power Amplifier With High Efficiency
In this project, basic study methods, in order to increase the efficiency and linearization of power amplifiers for future application are examined in digital communication systems. The emphasis is on standard GSM WCDMA (UMTS). The simultaneous fulfillment of efficiency and linearity can not be achieved with today's conventional amplifiers and methods. A completely different approach to solving the problem is the LINC (Linear Amplification using Nonlinear Components) method dar. This is a general signal that is encoded in today's systems with an amplitude and phase modulation in two entirely separated phase-modulated (AM) signals with a constant envelope. The two PM signals operates at constant amplitude with two amplifiers, which can be nonlinear and should be reinforced in compression and work with maximum efficiency, without causing intermodulation distortion. Finally, the two signals, by means of vector addition, can be reassembled into the original signal. A LINC system can be separated in different parts of different problems:
- DCS - broadband digital component separator in real time,
- Transmitter architecture,
- High-efficiency power amplifier in saturation,
- Last module power efficient amplifier combining output stages,
- Digital system calibration and signal correction (signal pre-distortion).
The digital component separator (DCS) are calculated in real time amplitude and phase information of the signal and derives the necessary two phase modulated signals. This was performed using an efficient DSP architecture designed in a very fast digital hardware (FPGA) with high bandwidth (120 MHz) for use in a LINC system and implemented. It was also shown, that the LINC technique is also suitable for transmitting multi-carrier signals (base station) efficiently. A complex modulation with a first digital intermediate frequency is required. This flexibility is also implemented on the FPGA. At the same time, an efficient and flexible configuration and adaptation to different RF transmitter topologies is supplied. The effect on the signal distortion as a function of bandwidth and the bandwidth requirements of the PM was investigated as a function of the amplitude modulation statistics and application as a single carrier (uplink) and for multi-carrier (downlink) transmission was specified. To achieve high efficiency, a special performance module addition, the amplifier output stages (Class B, C, F-operating) are necessary to the leads in practice to nonlinear signal distortion. Further research topic is to study the possibilities of a broadband digital linearization of the characteristic and the transmission channels, while maintaining a high overall efficiency. For this purpose, various methods are considered in the frequency domain. As a special condition vectorial measurement system was developed which has a real-time bandwidth of up to 60 MHz.
- Dipl.-Ing. Walter Gerhard
- Phone: 0431 / 880-6167
- E-mail: email@example.com
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