Lumped-Element Doherty Amplifier for Broadband Phase Shifting
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Solution Overview
Problem
Doherty amplifiers are large in size due to the use of quarter-wave transmission lines, which limits miniaturization and increases the size of microwave amplifiers, and existing solutions with varactor-based impedance transformers are complex and have bandwidth limitations.
Innovation Solution
The use of lumped-parameter all-path filters instead of quarter-wave transmission lines to achieve a 90-degree phase shift, allowing for a compact design and enhanced bandwidth by replacing one of the quarter-wave transmission lines with a filter circuit formed by lumped-parameter elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If quarter-wave transmission lines are used in the Doherty amplifier, then the amplifier achieves proper phase shifting and impedance transformation, but the amplifier becomes large in size
Solution Approach 1:
The patent replaces the physical quarter-wave transmission lines with an all-pass filter circuit that uses lumped-parameter elements (inductors and capacitors). This substitution transforms the mechanical/distributed structure into an electronic/lumped structure, achieving the same 90-degree phase shift and impedance transformation functions while dramatically reducing the physical size of the amplifier.
Solution Approach 2:
The patent changes the operating parameters of the filter circuit to achieve broadband performance. By carefully selecting the L and C values in the all-pass filter, the circuit maintains 90-degree phase shift across a wide frequency range, replacing the narrowband quarter-wave transmission line with a broadband alternative.
2Adaptability or versatility
If quarter-wave transmission lines are used, then the amplifier structure is simple, but the bandwidth is limited
Solution Approach 1:
The all-pass filter circuit using lumped-parameter elements provides broadband phase shifting capability, replacing the frequency-sensitive quarter-wave transmission line. The filter's transfer function is designed to maintain 90-degree phase shift over a wide frequency range, achieving superior bandwidth performance.
Solution Approach 2:
The all-pass filter circuit serves multiple functions simultaneously: it provides 90-degree phase shift, performs impedance transformation, and enables broadband operation. This multi-functional approach replaces what would traditionally require separate components, achieving versatility while managing complexity.
3Volume of moving object
If varactor-based impedance transformers are used to replace quarter-wave lines, then the amplifier size is reduced, but the structure becomes complex and bandwidth is limited
Solution Approach 1:
The patent uses fixed L and C values in the all-pass filter circuit to achieve broadband performance, avoiding the need for voltage-controlled varactors. This parameter selection strategy maintains compact size while eliminating the complexity and bandwidth limitations associated with adaptive impedance transformation circuits.
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
This approach results in a smaller Doherty amplifier size, reduced passage loss, and improved high-power efficiency while maintaining linearity and bandwidth, enabling efficient microwave signal amplification across a wide frequency range.
Implementation Method 1
a first filter circuit provided in an output side of the carrier amplifier, and through which all-frequency-range component of an amplified signal from the carrier amplifier passes and which shifts a phase of the amplified signal 90 degrees
Implementation Method 2
a second filter circuit through which all-frequency-range component of another output signal from the distributor passes and which shifts a phase of the output signal 90 degrees
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3A~3B
AI summary
According to one embodiment, a Doherty amplifier (1) includes: a distributor (11) which distributes a high-frequency signal inputted into two; a carrier amplifier (12) which amplifies one output signal from the distributor (11); a first filter circuit (13) through which an all-frequency-range component of an amplified signal from the carrier amplifier (12) passes, and which shifts a phase of the amplified signal; a second filter circuit (14) through which an all-frequency-range component of another output signal from the distributor (11) passes, and which shifts a phase of the another output signal, a peak amplifier (15) which amplifies an output signal from the second filter circuit (14); and a combiner (16) which combines an amplified signal from the peak amplifier (15) and an output signal from the first filter circuit (13). At least one of the first filter circuit (13) and the second filter circuit (14) is constituted by lumped-parameter elements.