Harmonic-Tuned Doherty Amplifier for Efficiency and Linearity
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Solution Overview
Problem
Conventional Doherty amplifiers face efficiency deterioration when operating at high peak-to-average ratio signals, such as in WCDMA or Wibro, due to poor linearity and harmonic distortion, especially when the fundamental load impedance is greater than 50Ω.
Innovation Solution
A Doherty amplifier with harmonic-tuned impedance networks for both the carrier and peaking amplifiers, which includes input and output harmonic impedance tuning networks to optimize harmonic impedances, ensuring efficient signal amplification and maintaining linearity by tuning second and third harmonic impedances to near open or short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-efficiency power amplifier is used, then efficiency is improved, but harmonic components and distortion occur in output signals
Solution Approach 1:
The patent converts the harmful harmonic components generated by high-efficiency amplifiers into beneficial elements by using them for load modulation in the Doherty configuration. The second harmonic components from the carrier amplifier are utilized to modulate the load impedance of the peaking amplifier, transforming distortion into a functional mechanism for improving overall efficiency across varying signal levels.
Solution Approach 2:
The patent changes the impedance parameters at harmonic frequencies to control distortion. By setting specific impedance values at the second harmonic frequency (open circuit or short circuit conditions) and adjusting fundamental frequency impedance, the system optimizes both efficiency and linearity. The load impedance is dynamically modulated based on signal power levels to maintain optimal operating conditions.
2Reliability
If a power amplifier operates at a few dB back-off from peak power to satisfy linearity, then linearity is improved, but efficiency deteriorates
Solution Approach 1:
The patent divides the amplification function into two separate amplifiers operating at different power levels. The carrier amplifier handles the average power level with optimized linearity, while the peaking amplifier handles peak power excursions. This segmentation allows each amplifier to operate in its optimal efficiency region, with the carrier amplifier running at higher back-off for linearity and the peaking amplifier providing high-efficiency peak power amplification when needed.
Solution Approach 2:
The patent implements periodic load modulation where the load impedance presented to the carrier amplifier varies periodically with the signal envelope. During low-power periods, the carrier amplifier operates alone with optimized impedance for linearity. During high-power periods, the peaking amplifier activates and the load impedance is modulated to combine outputs constructively, maintaining efficiency during peak transmissions.
3Power
If the fundamental load impedance is greater than 50Ω, then output power is improved, but harmonic distortion increases
Solution Approach 1:
The patent applies different impedance parameters at different frequency components. The fundamental frequency load impedance is set greater than 50Ω to maximize output power, while the second harmonic frequency impedance is specifically controlled (set to open circuit or short circuit conditions) to minimize harmonic distortion. This frequency-selective parameter optimization allows simultaneous achievement of high power and low distortion.
Data Source
AI summary
Disclosed is a Doherty amplifier including a carrier amplifier to perform a signal amplification operation regardless of a level of an input signal, a peaking amplifier to perform an amplification operation, starting from a high power output where a level of an input signal is equal to or greater than a predetermined level, an output combination circuit to combine and output the outputs of the carrier amplifier and the peaking amplifier, and an input division circuit to divide an input signal into the carrier amplifier and the peaking amplifier, the Doherty amplifier including a carrier amplifier output harmonic impedance tuning network installed at a rear end of the carrier amplifier to tune an output harmonic impedance of the carrier amplifier, and a peaking amplifier output harmonic impedance tuning network installed at a rear end of the peaking amplifier to tune an output harmonic impedance of the peaking amplifier.