Doherty RF Amplifier Phase Control for Wideband Multi-Band Operation
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Solution Overview
Problem
Existing high power Doherty amplifiers are limited to single-band operation due to bandwidth constraints, inefficiencies, and design limitations such as reliance on fixed frequency structures, non-inverting topologies, and excessive phase shifting elements, making them unsuitable for multi-band operation in wireless communication systems.
Innovation Solution
A radio frequency (RF) amplifier structure employing inverting and non-inverting Doherty designs with adjustable phase delay circuits and low pass multiple section inductance-capacitance circuits for impedance matching, enabling impedance inversion and efficient power handling across a wide bandwidth, and using frequency-adjustable phase shifters to optimize performance across multiple frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed frequency limiting quarter-wave transmission structures are used for Doherty load modulation, then the amplifier achieves good linearity and efficiency at a specific frequency, but the bandwidth is limited and cannot cover multiple commercial bands
Solution Approach 1:
The patent replaces fixed frequency quarter-wave transmission structures with dynamically adjustable phase delay circuits and impedance transformation networks. These components can be electronically tuned to adapt to different frequency bands, allowing the amplifier to maintain optimal performance across multiple bands rather than being locked to a single frequency.
Solution Approach 2:
The invention changes the operational parameters of the amplifier by introducing adjustable phase delay and impedance transformation capabilities. By varying these parameters electronically, the amplifier can be optimized for different frequency bands, thereby expanding bandwidth while maintaining linearity and efficiency characteristics.
2Loss of energy
If classic non-inverting Doherty topology with higher than system impedance saturating load is used, then the amplifier achieves good efficiency at power back-off modes, but the bandwidth is limited and phase shifting elements are excessive
Solution Approach 1:
The patent inverts the classic non-inverting Doherty topology to create an inverting configuration. This inversion reduces the number of phase shifting elements required and simplifies the overall circuit architecture while maintaining the efficiency benefits at power back-off modes. The inverted topology naturally provides the required phase relationships with fewer components.
Solution Approach 2:
The invention extracts and removes excessive phase shifting elements from the classic Doherty topology. By taking out these redundant components and replacing them with more efficient impedance transformation networks, the device complexity is reduced while preserving the essential functionality and efficiency characteristics.
3Reliability
If multiple hybrid combiner based phase shifting elements are used in the output, then the amplifier achieves proper signal combining, but the output power loss increases and bandwidth is reduced
Solution Approach 1:
The patent introduces an intermediary impedance transformation network between the amplifier stages and the power combiner. This intermediary structure facilitates proper signal combining while minimizing power loss, replacing the need for multiple hybrid combiner based phase shifting elements that cause excessive losses.
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 enables highly efficient RF signal amplification across a wide bandwidth, allowing for multi-band operation while maintaining high power efficiency and linearity, thereby overcoming the limitations of prior art Doherty amplifiers.
Implementation Method 1
low pass multiple section inductance-capacitance circuits for impedance matching
Implementation Method 2
adjustable phase delay circuits to optimize performance across multiple frequency bands
Implementation Method 3
Doherty amplifiers combine good linearity and efficiency by operating an amplifier of a primary, or carrier, amplifier stage as, for example, class AB, in parallel with an auxiliary, or peaking, amplifier stage
Data Source
AI summary
A radio frequency (RF) amplifier structure provides highly efficient RF signal amplification across a wide bandwidth, when implemented in both inverting and non-inverting Doherty designs, by employing matching impedance transform circuits that comprise a low pass multiple section inductance-capacitance circuit and that provides impedance matching between the output of an amplifier device and a power combiner, wherein the output matching impedance transform circuit has approximately an odd multiple of 90 electrical degrees over the RF amplifier structure's frequency range of operation, and adjustable phase delay circuits that route an amplified RF signal to the power combiner and that are controllably adjusted based on a frequency of an RF input signal over an operating frequency range of the RF amplifier structure.