Negative Electrical-Length Compensation in Doherty Amplifiers
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Solution Overview
Problem
Conventional Doherty amplifiers face challenges in amplifying wideband signals due to parasitic elements connected to the output stages of amplifying elements, which alter output phases and narrow the bandwidth, making it difficult to achieve high power efficiency.
Innovation Solution
A Doherty amplifier design incorporating phase compensation circuits with negative electrical lengths to adjust signal phases, allowing the electrical length from the amplifying elements to the power combiner to be 180°×N−90° and 180°×M−180°, respectively, to compensate for parasitic elements and maintain high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If parasitic elements are connected to the output stage of amplifying elements, then the amplifier can operate with high power efficiency, but the output phases are altered and the bandwidth becomes narrower
Solution Approach 1:
The patent applies preliminary anti-action by introducing phase compensation circuits with negative electrical lengths before the signals reach the combining terminal. These circuits pre-compensate for the phase shifts caused by parasitic elements, allowing the amplifier to maintain both high power efficiency and wide bandwidth by counteracting the harmful phase alterations in advance
2Loss of energy
If the electrical length from amplifying elements to combining terminal is increased to accommodate parasitic elements, then the amplifier can maintain high power efficiency, but the pass characteristics become narrower in bandwidth
Solution Approach 1:
The patent applies inversion by using phase compensation circuits with negative electrical lengths, which is the opposite approach of the conventional positive electrical length transmission lines. This inverted approach allows the system to achieve the required phase relationships while effectively reducing the total electrical length of the signal transmission path, thereby maintaining wide bandwidth characteristics
3Device complexity
If conventional transmission lines with positive electrical length are used, then the amplifier structure is simple, but it cannot compensate for phase changes caused by parasitic elements
Solution Approach 1:
The patent applies parameter changes by transforming the electrical length parameter from positive (conventional transmission lines) to negative (phase compensation circuits). This parameter change enables the system to compensate for phase shifts caused by parasitic elements while maintaining a relatively simple amplifier structure, achieving both structural simplicity and phase accuracy
Data Source
AI summary
A Doherty amplifier includes a carrier amplifier, a peaking amplifier, and a phase compensation circuit. The carrier amplifier 11 includes a main amplifying element and a parasitic element, and the peaking amplifier includes an auxiliary amplifying element and a parasitic element. The phase compensation circuit has a negative electrical length that allows a total electrical length of a signal transmission path starting from an output source of the main amplifying element to a power combiner to become 180°×N−90° where N is a positive integer. In addition, a signal transmission path starting from an output source of the auxiliary amplifying element to the power combiner has an electrical length of 180°×M−180° where M is a positive integer.