Multistage Doherty Amplifier With Delayed Peaking Drive
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Solution Overview
Problem
Conventional power amplifiers, such as single-transistor class B or AB amplifiers, have low average efficiency when amplifying signals with high peak-to-average power ratio (PAR) due to inefficient DC power usage, while wideband Doherty amplifiers face challenges in maintaining high efficiency and bandwidth with varying transition point amplitudes and requiring complex input drive circuits.
Innovation Solution
The proposed solution involves a multistage Doherty amplifier arrangement with additional peaking amplifiers driven in-phase to optimize load resistances and impedance matching, using a cascade of quarter wavelength transmission lines to achieve high efficiency and consistent properties over large bandwidths, allowing for simple static gain and bias settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-transistor power amplifier is used, then the circuit complexity is low, but the average efficiency is low when amplifying signals with high peak-to-average power ratio
Solution Approach 1:
The amplifier is divided into multiple independent amplifier stages, each handling different portions of the signal spectrum. This segmentation allows each stage to operate efficiently at its optimal point while collectively covering the full bandwidth, resolving the contradiction between low complexity and high efficiency.
Solution Approach 2:
Multiple amplifier stages are combined in parallel to achieve both high efficiency and wide bandwidth. The merging of multiple simple amplifier circuits creates a composite system that maintains the simplicity of individual stages while achieving the efficiency benefits of multi-transistor architectures.
2Use of energy by moving object
If a Doherty amplifier arrangement is used, then the average efficiency is improved, but the transition point amplitude varies considerably within the bandwidth
Solution Approach 1:
The bandwidth is segmented into multiple frequency ranges, each handled by a dedicated amplifier stage. This segmentation prevents the transition point amplitude from varying across the entire bandwidth, as each stage operates independently with its own stable transition point within its specific frequency range.
3Adaptability or versatility
If wideband Doherty amplifiers with multiple amplifiers are used, then the bandwidth of high efficiency is increased, but the input drive circuits become more complex
Solution Approach 1:
The input drive circuit is segmented and distributed to each amplifier stage independently. Each stage receives its own simplified drive signal tailored to its specific frequency range, avoiding the need for a single complex drive circuit that would be required to control all stages uniformly.
Solution Approach 2:
Each amplifier stage is designed as a universal building block that can operate independently with a simple drive circuit. This multi-functionality allows the same simple stage design to be replicated across multiple frequency ranges, achieving wide bandwidth without increasing drive circuit complexity.
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 high-efficiency, wideband amplifiers with reduced transition point amplitude variation and optimized efficiency across the bandwidth, enabling simpler control and drive circuits while maintaining high performance.
Implementation Method 1
a cascade of quarter wavelength transmission lines coupled between an output of one of the three sub-amplifiers or amplifier stages (10 2 in this example, also referred to as the "main" amplifier) and an output node (15) of the amplifier arrangement
Implementation Method 2
The impedances of the cascade of transmission lines may be configured such that the impedances optimize the bandwidth of low ripple in a transimpedance from the main amplifier to a load
Implementation Method 3
They have high average efficiency for amplitude-modulated signals with high peak-to-average ratio (PAR) since they have a much lower average sum of RF output current magnitudes from the transistors at low amplitudes
Implementation Method 4
The reduced average output current is obtained by using two transistors that influence each other's output voltages and currents through a reactive output network (that is also coupled to the load)
Data Source
Figure 1a
Figure 1b~1d
Figure 1e
AI summary
An amplifier arrangement comprises N amplifier stages (101 to 10 N) comprising a main amplifier stage and a plurality of peaking amplifier stages. A transmission line comprises a varying impedance (13) for transforming a load impedance to a higher impedance at the main amplifier stage, wherein the plurality of peaking amplifiers are coupled at intermediate locations to the transmission line. The amplifier arrangement is configured such that at least two of the peaking amplifiers are collectively driven with time delayed versions of substantially the same signal. The amplifier arrangement may be configured to operate with N-2 or fewer transition points in a Doherty mode of operation. As such, the amplifier arrangement may comprise more amplifier stages than are necessarily required in a Doherty amplifier arrangement having the same number of transition points.