Quadrature Doherty Amplifier Layout for Load-Mismatch Linearity
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Solution Overview
Problem
Doherty amplifiers face challenges in maintaining linearity and efficiency when driving mismatched loads, leading to increased adjacent channel leakage ratio (ACLR) and out-of-band emissions, particularly in RF communication systems.
Innovation Solution
The implementation of a quadrature combined Doherty amplifier, which separates an RF input signal into pairs of input signal components with quadrature phase relationships and uses cascode amplification stages in both peaking and carrier amplification stages, along with a combiner to generate an RF output signal, thereby achieving balanced amplification and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a Doherty amplifier drives a mismatched load, then power amplification is achieved, but linearity deteriorates and adjacent channel leakage ratio increases
Solution Approach 1:
The amplifier is divided into two separate Doherty amplifier paths (first and second Doherty amplifiers) that process different pairs of signal components. Each path independently handles amplification, and their outputs are combined. This segmentation allows each amplifier to operate with improved linearity while maintaining overall power output.
Solution Approach 2:
The patent employs quadrature phase relationships where the first pair of input signal components has a phase difference of about ninety degrees, and the second pair also has a phase difference of about ninety degrees. This asymmetric phase configuration enables the amplifiers to counteract distortion products through destructive interference, improving linearity under mismatched load conditions.
2Power
If a Doherty amplifier operates under mismatched load, then power output is maintained, but out-of-band emissions increase
Solution Approach 1:
The patent converts the harmful intermodulation distortion products generated by each Doherty amplifier into beneficial cancellation effects. By configuring the amplifiers in quadrature and combining their outputs, the distortion products from one path interfere destructively with those from the other path, reducing overall out-of-band emissions while maintaining power output.
3Reliability
If quadrature combined Doherty amplifiers are used, then distortion is reduced, but device complexity increases
Solution Approach 1:
The patent combines the outputs of two Doherty amplifier paths using a combiner that merges the first pair of amplified signal components with the second pair. This combining operation integrates the benefits of both paths, achieving distortion reduction through the quadrature configuration while consolidating the overall structure into a unified amplifier system.
Data Source
AI summary
Apparatus and methods for quadrature combined Doherty amplifiers are provided herein. In certain embodiments, a separator is used to separate a radio frequency (RF) input signal into a plurality of input signal components that are amplified by a pair of Doherty amplifiers operating in quadrature. Additionally, a combiner is used to combine a plurality of output signal components generated by the pair of Doherty amplifiers, thereby generating an RF output signal exhibiting quadrature balancing.