Doherty Power Amplifier Phase Shifting for Wide Back-Off Efficiency
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Solution Overview
Problem
Conventional Doherty amplifiers face challenges in achieving high efficiency over a wide range of output power levels and size reduction, particularly for devices like cellular phones, due to limitations in back-off range and circuit size, especially for signals with high Peak to Average Power Ratio (PAPR).
Innovation Solution
A power amplifier configuration that includes a distributor to split the input signal into two paths with a phase difference of about 2ϕ degrees (45<ϕ<90), a carrier amplifier, a peak amplifier, phase shifters to adjust signal phases, and a combiner to combine the signals, allowing the carrier amplifier to operate in a saturated state over a wider power range while reducing circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a λ/4 line is used in the Doherty amplifier, then the back-off range is widened and efficiency is improved, but the circuit size increases
Solution Approach 1:
The patent extracts and eliminates the λ/4 transmission line from the Doherty amplifier circuit while preserving the essential phase difference functionality through alternative phase shifting mechanisms, thereby reducing circuit size without sacrificing efficiency
Solution Approach 2:
The patent combines the phase shifting function previously provided by the λ/4 line with other circuit elements or integrated phase shifters, merging multiple functions into a more compact configuration that maintains the required 90-degree phase difference for wide back-off operation
2Volume of moving object
If the λ/4 line is removed to reduce circuit size, then the circuit is downsized, but the back-off range becomes small and efficiency deteriorates
Solution Approach 1:
The patent introduces intermediary phase shifting elements or circuits that mediate between the signal paths to create the necessary phase difference, replacing the λ/4 line's function with alternative mechanisms that achieve the same phase relationship in a more compact form
Solution Approach 2:
The patent changes the physical parameters of the phase shifting elements, such as using transmission lines with different electrical lengths or characteristic impedances, or using active phase shifters, to achieve the required 90-degree phase difference without requiring the physical dimensions of a λ/4 line
3Loss of energy
If the carrier amplifier operates in saturation state, then efficiency is improved, but the output power range is limited
Solution Approach 1:
The patent implements dynamic operation where the carrier amplifier transitions between saturation and linear states based on the input signal level, allowing the amplifier to maintain high efficiency during saturation while adapting to provide the full required output power range when operating in linear mode
Solution Approach 2:
The patent utilizes periodic modulation of the carrier amplifier's operating state, switching between saturation and linear regions in response to the envelope of the modulated signal, thereby achieving high efficiency for constant envelope portions while maintaining adaptability for varying power levels
Data Source
AI summary
A power amplifier includes a distributor distributing an input first signal to a second signal and a third signal delayed by about 2ϕ degrees (45<ϕ<90) from the second signal, a first amplifier amplifying the second signal and outputting a fourth signal when a first-signal power level is not lower than a first level, a second amplifier amplifying the third signal and outputting a fifth signal when the first-signal power level is not lower than a second level that is greater than the first level, a first phase shifter receiving the fourth signal and outputting a sixth signal delayed by about ϕ degrees from the fourth signal, a second phase shifter receiving the fifth signal and outputting a seventh signal advanced by about ϕ degrees from the fifth signal, and a combiner combining the sixth and seventh signals and outputting an amplified signal of the first signal.