Doherty Power Amplifier Harmonic Load Modulation for Lower IMD3
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Solution Overview
Problem
Doherty power amplifiers face significant deterioration in third-order intermodulation distortion (IMD3) due to unwanted clipping of the current at saturation, leading to non-linearity, especially in the output back-off region, which is critical for modern wireless communication systems with high peak-to-average power ratios (PAPRs) and wideband operation.
Innovation Solution
The implementation of a Doherty-like power amplifier with harmonic-modulated impedance inverters that modulate both fundamental and harmonic terminations, including second and third harmonic frequencies, to prevent clipping and achieve negative resistance conditions, thereby improving linearity and efficiency. This design includes phase compensation and post-matching circuits to manage impedance and prevent harmonic current leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Doherty power amplifier design is used, then power amplification is achieved, but third-order intermodulation distortion (IMD3) deteriorates significantly due to unwanted clipping of the current
Solution Approach 1:
The patent changes the termination parameters at harmonic frequencies (second and third harmonics) by introducing modulated harmonic terminations through impedance inverters. This transforms the drain termination conditions to achieve negative resistance at specific harmonics, preventing current clipping and reducing IMD3 while maintaining power amplification functionality.
Solution Approach 2:
The patent introduces dynamic modulation of harmonic terminations using impedance inverters controlled by the main and auxiliary power amplification devices. The terminations at second and third harmonic frequencies are dynamically adjusted based on the operating state, enabling the system to maintain optimal linearity across different power levels and prevent clipping during saturation.
2Use of energy by moving object
If power amplifiers operate at saturation to achieve high efficiency, then efficiency is improved, but linearity deteriorates due to current clipping in the output back-off region
Solution Approach 1:
The patent modifies the harmonic termination parameters dynamically to maintain negative resistance conditions at second and third harmonics during saturation operation. This parameter transformation prevents the current clipping that normally occurs at saturation, allowing the amplifier to maintain both high efficiency and high linearity across the output back-off region.
3Loss of information
If modern wireless communication systems use high peak to average power ratios (PAPRs), then signal fidelity is improved, but the requirement for high efficiency and high linearity in the output back-off region becomes more stringent
Solution Approach 1:
The patent transforms the harmonic termination parameters to achieve negative resistance conditions that prevent current clipping specifically in the output back-off region. This allows the amplifier to handle high PAPR signals with maintained linearity and efficiency, as the modulated harmonic terminations adapt to the varying power levels characteristic of high PAPR modulation schemes.
Data Source
AI summary
A power amplifier including: a main power amplification device having an output; an auxiliary power amplification device having an output; a load modulation circuit operably connected to the output of the main power amplification device and the output of the auxiliary power amplification device; and a post-matching circuit operably connected to load modulation circuit. The load modulation circuit is arranged to enable fundamental frequency load modulation and to enable modulated harmonic terminations of at least the second and third harmonic frequencies. The modulated harmonic terminations may include drain terminations.