Background and Objectives: In order to compensate the nonlinearity, several linearization approaches such as feedback, feed-forward, and predistortion have been proposed. Among these linearization methods, the analog predistortion (APD) method is very suitable for the power amplifier and TWTA linearization, because it has a good compromise between complexity, linearity improvement and bandwidth. On the other hand, analog predistortion circuit can be added to existing amplifiers as a separate circuit. Many of the reported linearizer circuits are capable of linearizing power amplifiers with high gain and phase variations. However, these circuits are complex and bulky due to the use of distortion producer, phase shifter, adjustable attenuator, combiner/divider, and control unit. The objective of this paper is increasing the dynamic range of the predistorter by a simple proposed circuit. Hence, linearization capability of the linearizer is boosted.
Methods: A new analog predistortion linearizer based on a coupler and a Schottky diode is presented. The proposed structure satisfies linearization requirements of the solid-state power amplifiers (SSPAs) and traveling wave tube amplifiers (TWTAs). Using a parallel combination of two Schottky diodes along with transmission line in port 2 and 3 of the coupler, the dynamic range of reflection coefficient of each port is increased compared to using a single diode in each branch. By increasing the range of reflection signal, the linearization capability has been increased to linearize power amplifiers and TWTAs. The AM/AM and AM/PM of the linearizer is controlled by changing the bias voltage of power supply.
Results: The simulation results show that about 30° phase shift and 5 dB gain expansion can be compensated for power amplifiers and TWTAs. Because of utilizing two diodes, the linearization capability of the new linearizer is augmented compared to the conventional linearizer.
Conclusion: A novel analog predistortion circuit based on the hybrid coupler and Schottky diodes is presented. The suggested topology increases the dynamic range of reflected power from each port. Using the proposed idea, AM/AM and AM/PM characteristics are expanded such that this characteristic can linearize the power amplifier with high linearity.
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