Distributed Power Amplifier With Auto-Transformer Output Combining
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Solution Overview
Problem
CMOS power amplifiers face challenges in delivering sufficient RF power due to low breakdown voltage and high peak-to-average power ratio in OFDM-based modulation schemes, leading to reduced power efficiency, especially in mobile handsets where space constraints limit the implementation of Doherty-type PAs and distributed active transformers.
Innovation Solution
A distributed power amplifier circuit utilizing a chain of auto transformers to combine output signals from multiple sub-amplifiers, with each auto transformer having inductor segments and a capacitor for efficient power supply and configuration switches to enable/disable sub-amplifiers based on power requirements, improving power efficiency and reducing insertion losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CMOS transistors are used for power amplifiers, then cost is reduced, but RF power delivery capability deteriorates due to low breakdown voltage
Solution Approach 1:
The power amplifier is divided into multiple sub-amplifier stages, each operating at lower power levels with CMOS transistors. By segmenting the overall power amplification function across multiple stages with progressively higher power levels (using CMOS for lower stages and LDMOS for higher stages), the system achieves high total power output while maintaining the cost advantage of CMOS technology for the majority of the amplification chain.
2Reliability
If output power is backed off from peak level, then linearity is improved for OFDM modulation, but power efficiency deteriorates
Solution Approach 1:
The power amplifier employs dynamic operation where different sub-amplifier stages are selectively activated based on the instantaneous signal power level. During low-power portions of the OFDM signal, only the most efficient stages are active, while during peak power portions, additional stages are dynamically engaged. This dynamic allocation of amplification resources maintains linearity through proper biasing while maximizing power efficiency by avoiding operation in the inefficient backed-off region.
3Use of energy by moving object
If Doherty-type PAs are used, then power efficiency is improved, but device complexity and space requirements worsen
Solution Approach 1:
The amplifier is segmented into multiple independent sub-amplifier stages, each capable of operating autonomously. This segmentation replaces the complex Doherty architecture with a modular cascade of simpler amplifier stages, reducing overall circuit complexity while maintaining power efficiency through selective activation of stages based on operating conditions.
Solution Approach 2:
Each sub-amplifier stage is designed with universal characteristics that allow it to function effectively across different power levels and operating conditions. The stages can be individually configured and activated to serve multiple functions (power amplification, impedance matching, biasing) depending on the operational requirements, eliminating the need for specialized Doherty circuit elements.
4Use of energy by moving object
If multiple sub-amplifiers are combined, then power efficiency is improved, but insertion losses worsen
Solution Approach 1:
Multiple sub-amplifier stages are merged in a cascaded configuration where the output of one stage directly feeds the input of the next. This merging approach minimizes the number of intermediate coupling elements and transmission lines between stages, thereby reducing cumulative insertion losses while maintaining the power efficiency benefits of multi-stage operation.
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 enhances power efficiency by optimizing power supply and enabling/disabling sub-amplifiers, reducing insertion losses, and allowing for adaptable power levels, thus improving battery life and heat management in battery-powered devices.
Implementation Method 1
The auto transformers are operatively connected in series via said interconnection terminals, thereby forming a chain of auto transformers
Implementation Method 2
Each auto transformer comprises a first inductor segment between its first interconnection terminal and a first input terminal of the auto transformer
Implementation Method 3
Each auto transformer comprises a second inductor segment between its first input terminal and a second input terminal of the auto transformer
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A distributed power amplifier circuit comprises an amplifier arrangement (100) comprising a plurality of sub amplifiers (110_1 - 110_N), each having an output port (120_1 - 120_N) for outputting an output signal of the sub-amplifier (110_1 - 110_N) and an output combiner network (200) for combining the output signals from the sub amplifiers (110_1 - 110_N). The output combiner network (200) comprises, for each sub amplifier (110_i), an associated auto transformer (210_i) operatively connected to the output port (120_i) of the sub amplifier (110_i) for receiving the output signal of the sub amplifier (110_i). The auto transformers (210_1 - 210_N) each have a first interconnection terminal (240_1 - 240_N) and a second interconnection terminal (230_1 - 230_N). The auto transformers (210_1 - 210_N) are operatively connected in series via said interconnection terminals (230_1 - 230_N; 240_1 - 240_N).