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Logo: Institute of Microwave and Wireless Systems
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Logo: Institute of Microwave and Wireless Systems
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Radio Frequency Power Amplifiers

In modern communication systems exist stringent requirement on linearity and efficiency in, e.g., a mobile transmitter or a base station. The radio frequency power amplifier of a base station is the part with the highest DC power consumption. In stationary as well as in mobile communication system applications the DC power consumption of the RF power amplifier influenced the cooling cost and the battery lifetime. Therefore, the maximal efficiency of the power amplifiers should be increase, e.g., through the use of Class F or inverse Class F. The efficiency enhance is achieved only at the maximum RF output power. An efficiency enhancement over the dynamic range is furthermore necessary, through the high peak-to-average power ratio (PAPR) of the complex modulation scheme. A possible approach to enhance the efficiency for signals is the Doherty power amplifier. The efficiency requirement comply with the Doherty power amplifier. The linearity of the efficient power amplifier can be improved through a digital predistortion (DPD).

The Institute of Microwave and Wireless Systems is working within the topics of efficient power amplifiers and waveform engineering respectively nonlinear measurement techniques. 

Efficient Power Amplifiers

In general a power amplifier has the highest efficiency at maximum output power near the saturation region. However, through the high peak-to-average power ratio, which result in modern communication systems with high data rates, a high efficiency in the back-off range is required. The efficiency can be enhanced with different techniques and topologies.

Possible solution to enhance the efficiency in the range of the average power is a variation of the load impedance of the transistor. This variation can be realized with an adaptive matching network or automatically with a Doherty amplifier.

The complex modulation scheme, which are implemented in modern communication systems to transmit the high data rates, requires a linear amplification. However, high efficient power amplifiers works in the saturation range and generated in band and out of band distortion. To linearize the nonlinear power amplifier various techniques can be used. In the following only linearization techniques and topologies are discussed, which are based on digital base band processing.

Waveform Engineering

Amplifier architectures are commonly complex circuits. Normally an amplifier is characterized by measuring input and output quantities and the direct current (DC) operation point. However, in some instances these quantities do not deliver enough knowledge to the developer about the grounds on which the performance of the power amplifier is based.

Furthermore, knowledge about the high frequency voltages and currents (waveforms) is important at all levels of the design process, e.g., for the verification of the circuit design and its compliance with the system requirements.

An application for the in situ measurement approach is the measurement of the interaction of the carrier and the peak amplifier in a Doherty amplifier, e.g., in the package plane of the transistor.

Efficient Power Amplifiers

In general a power amplifier has the highest efficiency at maximum output power near the saturation region. However, through the high peak-to-average power ratio, which result in modern communication systems with high data rates, a high efficiency in the back-off range is required. The efficiency can be enhanced with different techniques and topologies.

Possible solution to enhance the efficiency in the range of the average power is a variation of the load impedance of the transistor. This variation can be realized with an adaptive matching network or automatically with a Doherty amplifier.

The complex modulation scheme, which are implemented in modern communication systems to transmit the high data rates, requires a linear amplification. However, high efficient power amplifiers works in the saturation range and generated in band and out of band distortion. To linearize the nonlinear power amplifier various techniques can be used. In the following only linearization techniques and topologies are discussed, which are based on digital base band processing.

Waveform Engineering

Amplifier architectures are commonly complex circuits. Normally an amplifier is characterized by measuring input and output quantities and the direct current (DC) operation point. However, in some instances these quantities do not deliver enough knowledge to the developer about the grounds on which the performance of the power amplifier is based.

Furthermore, knowledge about the high frequency voltages and currents (waveforms) is important at all levels of the design process, e.g., for the verification of the circuit design and its compliance with the system requirements.

An application for the in situ measurement approach is the measurement of the interaction of the carrier and the peak amplifier in a Doherty amplifier, e.g., in the package plane of the transistor.

References

[1] S. Probst, E. Denicke, B. Geck (2017): In Situ Waveform Measurements within a Doherty Power Amplifier under Operational Conditions, IEEE Transaction on Microwave Theory and Techniques, Vol. 65, No. 6, pp. 2192 - 2200, June 2017 DOI: 10.1109/TMTT.2017.2651809

[2] S. Probst, B. Geck (2015): In Situ Waveform Measurement Approach within an Inverse Class F GaN Power Amplifier, International Workshop on Integrated Nonlinear Microwave and Millimetre-wave Ciruits 2015 (INMMiC 2015), Taormina (Messina), Italy, October 1-2, 2015
DOI: 10.1109/INMMIC.2015.7330360