Wideband Doherty Amplifier Combiner for Backoff Efficiency
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Solution Overview
Problem
Doherty amplifiers face efficiency degradation between peak output backoff and peak power points, and are typically narrowband due to band-limiting characteristics of quarter-wavelength transmission lines, limiting their application to specific frequency bands.
Innovation Solution
A three-way wideband Doherty amplifier circuit employing a constant impedance combiner that maintains transformed impedance across all nodes, reducing band limiting and enabling operation across wider frequency ranges by matching the main amplifier's impedance in the high impedance load modulated state, allowing for simultaneous coverage of multiple adjacent bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If quarter-wavelength transmission lines are used for impedance transformation, then impedance matching is achieved, but bandwidth is limited
Solution Approach 1:
The quarter-wavelength transmission line is segmented into two sections with different characteristic impedances. The first section has impedance Z1 and the second section has impedance Z2, where Z1 ≠ Z2. This segmentation allows the combiner to provide different impedance transformations at different frequency ranges, thereby extending the overall bandwidth while maintaining proper impedance matching at the amplifier output.
2Use of energy by moving object
If highly asymmetric ratio between main and peaking amplifiers is used, then efficiency at high output backoff is improved, but efficiency degradation between peak OBO and peak power points occurs
Solution Approach 1:
The peaking amplifier function is segmented into two separate peaking amplifiers with different power levels. The first peaking amplifier handles the transition from peak OBO to peak power, while the second peaking amplifier handles higher power levels. This segmentation allows each peaking amplifier to operate in its optimal efficiency range, maintaining high efficiency across the entire power backoff range without the efficiency degradation that occurs in single-stage designs.
3Use of energy by moving object
If three way Doherty architecture is used, then efficiency between peak OBO and peak power points is improved, but band limiting characteristics are introduced
Solution Approach 1:
Different sections of the combiner are designed with different characteristic impedances to provide locally optimized impedance transformation for different frequency ranges. The first transmission line section is optimized for lower frequencies while the second section is optimized for higher frequencies, allowing the overall system to maintain both high efficiency and wide bandwidth across the entire operating band.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves more constant power and efficiency versus frequency at fixed backoff power levels, making the amplifier suitable for wider band applications and reducing bandwidth limitations, thus enhancing performance across multiple frequency bands.
Implementation Method 1
The constant impedance combiner is operable to transform a load impedance at the fourth node to a transformed impedance at the third node, and maintain the same transformed impedance at the first, second and third nodes
Data Source
AI summary
An amplifier circuit includes a first amplifier operable to turn on at a first power level, a second amplifier operable to turn on at a second power level below the first power level and a third amplifier operable to turn on at all power levels. A first power combiner is operable to combine an output of the third amplifier with an output of the second amplifier at a first power combining node to form a first combined amplifier output. A second power combiner is operable to combine the first combined amplifier output with an output of the first amplifier at a second power combining node to form a second combined amplifier output. An impedance transformer is operable to transform a load impedance of the amplifier circuit to a transformed impedance at the second power combining node, the transformed impedance matching an impedance of the first and second power combiners.