Multiple-Pole Input Impedance Matching Circuit for RF Power Amplifiers
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Solution Overview
Problem
Conventional RF power amplifiers for cellular base stations face limitations due to impedance dispersion and quality factor limitations across multiple frequency bands, particularly in Doherty amplifier designs, where single-pole input impedance matching circuits result in high impedance dispersion and phase linearity variations.
Innovation Solution
Implementing a multiple-pole input impedance matching circuit within the RF amplifier's bandwidth, with at least one pole located between the lower and upper cutoff frequencies and another outside the bandwidth, to enhance bandwidth and in-band gain flatness, and achieve near-zero linear phase distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-pole input impedance matching circuit is used, then the device complexity is reduced, but the bandwidth and impedance matching performance deteriorate due to high impedance dispersion
Solution Approach 1:
The input impedance matching circuit is segmented into multiple poles (at least two poles) instead of using a single pole. This segmentation allows each pole to contribute to different aspects of impedance matching across the frequency band, thereby expanding the overall bandwidth and reducing impedance dispersion while maintaining manageable circuit complexity through modular design.
2Ease of manufacture
If a single-pole input impedance matching circuit is used, then the manufacturing is simpler, but the in-band gain flatness deteriorates due to quality factor limitations
Solution Approach 1:
The matching circuit uses multiple poles to divide the frequency coverage task, allowing each pole to be optimized for specific frequency ranges. This improves in-band gain flatness by distributing the matching function across multiple elements, reducing the burden on any single component and mitigating quality factor limitations.
Solution Approach 2:
The invention adjusts the parameters of the multiple poles (such as their frequencies and Q-factors) to optimize performance. By carefully selecting pole locations and characteristics, the circuit achieves improved in-band gain flatness and reduced phase linearity variation while remaining manufacturable with standard components.
3Device complexity
If a single-pole input impedance matching circuit is used, then the circuit design is simpler, but the phase linearity varies significantly across the band
Solution Approach 1:
The phase compensation function is distributed across multiple poles in the input impedance matching circuit. Each pole contributes to phase correction at different frequency ranges, resulting in improved overall phase linearity across the entire operating band. This segmented approach to phase control reduces the phase linearity variation that would occur with a single-pole design.
Data Source
AI summary
An embodiment of an amplifier has a bandwidth defined by low and upper cutoff frequencies. The amplifier includes an input impedance matching circuit and a transistor. The transistor has a gate, a first current conducting terminal coupled to an output of the amplifier, and a second current conducting terminal coupled to a reference node. The input impedance matching circuit has a filter input coupled to an input of the amplifier, a filter output coupled to the gate of the transistor, and a multiple pole filter coupled between the filter input and the filter output. A first pole of the filter is positioned at a first frequency within the bandwidth, and a second pole of the filter is positioned at a second frequency outside the bandwidth. The input impedance matching circuit is configured to filter the input RF signal to produce a filtered RF signal at the filter output.