Frequency-Switched Doherty Amplifier for Back-Off Efficiency
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Solution Overview
Problem
Doherty amplifiers experience a decrease in efficiency during back-off operations when signals with frequencies different from the 90-degree electrical length of the output-side line of the carrier amplifier are used.
Innovation Solution
A Doherty amplifier design that includes a first amplifier operating as an auxiliary or main amplifier based on signal frequency, with a second amplifier having higher saturated output power, and a combiner that transforms output impedance to reduce imaginary components, maintaining efficiency across varying frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a 90-degree line is used to achieve 90-degree electrical length at first frequency, then efficiency during back-off operation is improved at first frequency, but efficiency decreases at second frequency due to imaginary component increase
Solution Approach 1:
The patent applies dynamics by making the electrical length of the output-side line frequency-dependent. Instead of a fixed 90-degree line, the system is designed so that the electrical length varies with frequency, allowing the line to provide 90-degree electrical length at the first frequency while accepting different electrical lengths at other frequencies without causing efficiency degradation through excessive imaginary components.
Solution Approach 2:
The patent changes the parameter of electrical length from a fixed value to a frequency-dependent value. By designing the output-side line with specific impedance and length characteristics, the electrical length becomes a function of frequency, enabling the system to maintain good matching conditions across multiple frequencies rather than being optimized for a single frequency only.
2Loss of energy
If saturated output power of peak amplifier is made larger than carrier amplifier, then efficiency at back-off operation is improved, but output reflection coefficient increases
Solution Approach 1:
The patent changes the parameter relationship between the two amplifiers by making their saturated output powers unequal, with the peak amplifier having larger saturated output power than the carrier amplifier. This parameter change allows the peak amplifier to provide better load modulation during back-off operations, improving efficiency while the combiner design compensates for the resulting reflection coefficient increase.
Data Source
AI summary
A Doherty amplifier includes: a first amplifier to amplify a first signal as an auxiliary amplifier in a case where a frequency of each of the first signal and a second signal is a first frequency, and amplify the first signal as a main amplifier in a case where the frequency of each of the first signal and the second signal is a second frequency; a second amplifier to amplify the second signal as a main amplifier in a case where the frequency of each of the first signal and the second signal is the first frequency, and amplify the second signal as an auxiliary amplifier in a case where the frequency of each of the first signal and the second signal is the second frequency; and a combiner to synthesize the first signal amplified by the first amplifier and the second signal amplified by the second amplifier.