Low-Pass Filter Combiner for Compact Broadband Doherty Amplifiers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Doherty amplifier combiners require extensive use of transmission lines, leading to bulky designs and limited bandwidth, which complicates integration and performance at lower frequencies.
Innovation Solution
A filter combiner design utilizing low-pass filters composed of lumped elements, which reduces the need for transmission lines, allowing for a more compact and broadband capable Doherty amplifier combiner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmission lines are used in the combiner design, then the combiner can achieve reactive combination of signals, but the physical size becomes large and bulky especially at lower frequencies
Solution Approach 1:
The patent replaces the mechanical transmission line system with an electrical filter network system. Instead of using physical transmission lines to achieve reactive combination, the invention uses a network of inductors and capacitors configured as filters to synthesize the required reactive impedances, thereby eliminating the need for bulky transmission lines while maintaining the signal combination function.
Solution Approach 2:
The patent changes the operating parameters from transmission line physical dimensions to electrical component values. By adjusting the values of inductors and capacitors in the filter network, the required reactive impedances are achieved through electrical parameter optimization rather than mechanical dimensioning, enabling compact design at lower frequencies.
2Reliability
If transmission lines are used for signal combination, then reactive coupling can be achieved, but the bandwidth becomes limited and integration becomes difficult
Solution Approach 1:
The patent substitutes the transmission line-based reactive coupling mechanism with an electrical filter network. This substitution enables broadband operation because the filter network can be designed to maintain its reactive characteristics over a wider frequency range compared to fixed-length transmission lines, and facilitates integration using standard PCB mounting techniques for discrete components.
Solution Approach 2:
The filter network serves multiple functions: it provides reactive coupling, defines impedance transformations, and can be designed to operate across broad frequency ranges. This multi-functionality replaces the specialized transmission line approach with a more versatile electrical network that adapts to different operating conditions and integration requirements.
3Reliability
If quarter-wave transmission lines are used to bring signals back into phase, then phase alignment is achieved, but the combiner becomes narrow banded and bulky
Solution Approach 1:
The patent replaces quarter-wave transmission lines with an electrical filter network comprising inductors and capacitors. This network synthesizes the required phase shifts and impedance transformations through electrical reactances rather than physical transmission line lengths, achieving phase alignment without the narrow bandwidth and bulk associated with quarter-wave structures.
Data Source
AI summary
A filter combiner for a Doherty amplifier includes a first port with an impedance of Z0 configured to be connected to an output of a carrier amplifier; a second port with an impedance of Z0·r/(1+r) configured to be connected to a load; a third port with an impedance of Z0·r/(1+r) configured to be connected to a peak amplifier, wherein r is a power ratio for the carrier amplifier to the peak amplifier; and a fourth port with an impedance of Z0 configured to be connected to an output port of the Doherty amplifier. The first port is connected to the second port via a first network that is a lowpass filter and to the third port via a second network that is a lowpass filter which is configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The third port is connected to the fourth port via a third network that is a lowpass filter configured to operate as a band stop filter upon loading the input or the output of the second network with a high impedance when the peak amplifier is off. The fourth port is connected to the second port via a fourth network that is a lowpass filter.