Frequency-Adaptive Doherty Amplifier Combiner for Back-Off Efficiency
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Solution Overview
Problem
In Doherty amplifiers, efficiency decreases during back-off operations when the frequency of the signal provided to the distribution circuit is different from the fundamental frequency due to a mismatch in the electrical length of the output-side line of the carrier amplifier, leading to an increase in the imaginary component of the output impedance.
Innovation Solution
A Doherty amplifier configuration where the first amplifier operates as an auxiliary or main amplifier based on signal frequency, with a combiner transforming the output impedance to maintain efficiency by adjusting the electrical lengths of the output circuits and biasing classes of the amplifiers, ensuring the imaginary component is minimized or optimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a 90-degree line is used to set the electrical length of the output-side line of the carrier amplifier at the fundamental frequency, then the efficiency during back-off operation is improved at the fundamental frequency, but the efficiency decreases at the second frequency due to impedance mismatch
Solution Approach 1:
The patent introduces a variable electrical length configuration where the output-side line of the carrier amplifier has different electrical lengths at different frequencies (90 degrees at fundamental frequency, 45 degrees at second frequency). This dynamic adaptation allows the system to maintain optimal impedance matching and efficiency across multiple operating frequencies, resolving the contradiction between optimized performance at one frequency and adaptability to other frequencies.
Solution Approach 2:
The patent changes the electrical length parameter of the output-side line based on the operating frequency. By setting the electrical length to 90 degrees at the fundamental frequency and 45 degrees at the second frequency, the system optimizes the output reflection coefficient and minimizes the imaginary component of output impedance at each frequency, thereby maintaining high efficiency during back-off operations across different frequencies.
2Use of energy by moving object
If the electrical length of the output-side line is fixed at 90 degrees for fundamental frequency operation, then back-off efficiency is optimized at the fundamental frequency, but the imaginary component of output impedance increases at the second frequency
Solution Approach 1:
The system dynamically adjusts the electrical length of the output-side line according to the operating frequency. At the fundamental frequency, the electrical length is 90 degrees to optimize back-off efficiency. At the second frequency, the electrical length is reduced to 45 degrees to maintain proper output impedance matching and minimize the imaginary component, thus resolving the contradiction between efficiency optimization and impedance matching precision.
Solution Approach 2:
The patent employs parameter changes by varying the electrical length of the output-side line based on frequency. This parameter adjustment ensures that the output reflection coefficient is optimized and the imaginary component of the output impedance is minimized at both the fundamental frequency and the second frequency, achieving precise impedance matching across different operating conditions.
Data Source
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AI summary
A Doherty amplifier includes: a first amplifier (9) 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 (10) 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 (11) to synthesize the first signal amplified by the first amplifier (9) and the second signal amplified by the second amplifier (10). In addition, the second amplifier (10) has a saturated output power larger than that of the first amplifier (9), and the combiner (11) transforms output impedance of the first amplifier (9) so that an imaginary component in the output impedance of the first amplifier (9) is reduced in a case where the first amplifier (9) amplifies the first signal as the main amplifier and the second amplifier (10) amplifies the second signal as an auxiliary amplifier.