Balanced RF Amplifier Using CM Chokes for Even Harmonic Suppression
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Solution Overview
Problem
Balanced amplifiers face challenges in suppressing even harmonics due to increased amplitude and phase imbalance caused by cascading stages and component variations in high volume manufacturing, leading to reduced gain and increased cost with the use of baluns.
Innovation Solution
The implementation of common mode (CM) chokes replaces baluns, improving amplifier balance and reducing even harmonics while being more power efficient and cost-effective, allowing for increased tolerance to amplitude and phase imbalance variations and enabling more amplifier stages without additional baluns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If baluns are added between cascaded amplifier stages to improve balance and reduce even harmonics, then even harmonic suppression is improved, but gain is lost, power efficiency is reduced, and cost increases
Solution Approach 1:
The patent removes baluns from the amplifier circuit and replaces them with common mode chokes. This extraction of the balun component eliminates the associated power loss, cost, and complexity while maintaining even harmonic suppression through the choke's common mode rejection特性
Solution Approach 2:
The common mode choke serves multiple functions: it suppresses even harmonics through common mode rejection, provides DC bias to the RF transistors, and maintains amplifier balance. This multi-functionality replaces what previously required separate baluns and bias circuitry
2Object-generated harmful factors
If baluns are added between cascaded amplifier stages to improve balance and reduce even harmonics, then even harmonic suppression is improved, but gain is lost, power efficiency is reduced, and cost increases
Solution Approach 1:
The patent removes baluns from the amplifier circuit and replaces them with common mode chokes. This extraction of the balun component eliminates the associated gain loss while maintaining even harmonic suppression through the choke's common mode rejection特性
Solution Approach 2:
The common mode choke is a simpler, more robust component compared to baluns, with fewer loss mechanisms. It provides the necessary even harmonic suppression without the gain penalty associated with balun transformations
3Object-generated harmful factors
If baluns are added between cascaded amplifier stages to improve balance and reduce even harmonics, then even harmonic suppression is improved, but device complexity and cost increase
Solution Approach 1:
The patent removes baluns from the amplifier circuit and replaces them with common mode chokes. This extraction reduces device complexity by eliminating the need for multiple balun components and their associated windings and cores
Solution Approach 2:
The common mode choke serves multiple functions: it suppresses even harmonics through common mode rejection, provides DC bias to the RF transistors, and maintains amplifier balance. This multi-functionality reduces the overall component count and circuit complexity
4Object-generated harmful factors
If tight PCB layout symmetry and component selection are used to achieve high amplitude and phase balance, then even harmonic suppression is improved, but manufacturing precision requirements and cost increase
Solution Approach 1:
The common mode choke acts as an intermediary that actively compensates for imbalances in the amplifier circuit. It suppresses even harmonics generated by amplitude and phase imbalances, thereby reducing the stringency of PCB layout symmetry and component matching requirements
Solution Approach 2:
The common mode choke provides a robust solution that tolerates manufacturing variations. It reduces the need for expensive tight-tolerance components and complex PCB layout procedures, enabling more relaxed manufacturing specifications
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
CM chokes enhance the Output-referred Second Order Intercept Point (OIP2) and power efficiency, reduce the need for filtering, and relax manufacturing precision requirements, resulting in lower costs and improved performance in wideband RF systems.
Implementation Method 1
CM chokes can be used to reduce second order harmonic spur levels on a wideband balanced RF amplifier
Data Source
AI summary
A balanced amplifier can utilize a common mode choke to suppress even harmonics in the signals of the balanced amplifier. The common choke can be coupled between cascaded balanced amplifier pairs to receive the differential output signals from one of the balanced amplifier pairs and to provide conditioned signals to the other of the balanced amplifier pairs. The common mode choke can improve the amplitude and phase balance between the differential output signals by providing increased impedance to the passage of common mode signals such as even harmonics.