Balun Circuit With Tertiary Winding for High-Frequency CMRR
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Solution Overview
Problem
Balun transformers at high frequencies experience parasitic capacitance between windings, leading to undesirable common-mode signals due to asymmetrical grounding, which degrades common-mode rejection ratio (CMRR) and affects signal power conversion.
Innovation Solution
Incorporating a third magnetically coupled winding with a floating terminal and strategically placed capacitors to counteract common-mode currents, ensuring equal capacitances between windings to nullify common-mode components and enhance CMRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional balun with asymmetrical grounding is used, then the structure is simple, but the common-mode rejection ratio (CMRR) degrades at high frequencies due to parasitic capacitance coupling
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetrical capacitive coupling structure. Specifically, a first capacitor is coupled between the primary and secondary windings, while a second capacitor is coupled between the tertiary and secondary windings, with the capacitors having different capacitance values. This deliberate asymmetry compensates for the parasitic capacitance effects and improves CMRR at high frequencies.
Solution Approach 2:
The patent introduces a tertiary winding as an intermediary element between the primary and secondary windings. This tertiary winding, with its associated capacitor, acts as a mediator to counteract the harmful parasitic capacitance coupling between the primary and secondary windings, thereby improving the common-mode rejection ratio without requiring complete redesign of the basic transformer structure.
2Power
If parasitic capacitance between windings is present, then magnetic coupling is achieved, but common-mode signals are generated at the secondary winding
Solution Approach 1:
The patent converts the harmful effect of parasitic capacitance into a beneficial effect by deliberately adding capacitors between the windings. The first capacitor (with different capacitance value) between primary and secondary windings, and the second capacitor between tertiary and secondary windings, are designed to exploit capacitive coupling to generate counteracting signals that cancel the unwanted common-mode signals produced by parasitic capacitance.
Solution Approach 2:
The patent changes the electrical parameters of the system by introducing capacitors with specific capacitance values. The first capacitor has a capacitance value different from the second capacitor, and these values are carefully selected to optimize the cancellation of common-mode signals while maintaining differential mode conversion gain, thereby improving CMRR at high frequencies.
3Adaptability or versatility
If asymmetrical grounding is used in the primary winding, then single-ended to differential conversion is enabled, but common-mode rejection is degraded due to capacitive coupling
Solution Approach 1:
The patent segments the coupling path between primary and secondary windings by introducing a tertiary winding as an intermediate stage. Instead of direct coupling that causes harmful parasitic effects, the signal path is divided into two stages: primary to tertiary coupling and tertiary to secondary coupling, with capacitors strategically placed at each stage to control and optimize the coupling characteristics.
Solution Approach 2:
The patent adds another dimension to the transformer structure by introducing a tertiary winding that provides an additional magnetic coupling path. This third dimension in the winding structure allows for more flexible control of capacitive coupling effects and enables the implementation of the asymmetrical capacitor network that improves CMRR while maintaining conversion capability.
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 significantly improves CMRR by reducing common-mode gain and maintaining high differential mode conversion, resulting in low amplitude and phase imbalance across a wide frequency range.
Implementation Method 1
a second winding magnetically coupled to the first winding; a third winding magnetically coupled to the first winding
Data Source
AI summary
A balun includes a first winding which has a first terminal coupled to an input, and a second terminal coupled to a reference potential terminal. The balun includes a second winding magnetically coupled to the first winding. The second winding has a first terminal coupled to a first differential output, a second terminal coupled to a second differential output, and a tap coupled to the reference potential terminal. The balun includes a first capacitor which has a first terminal coupled to the first winding and a second terminal coupled to the second winding. The balun includes a third winding which has a first terminal coupled to the reference potential terminal and a floating second terminal. The balun includes a second capacitor which has a first terminal coupled to the third winding and a second terminal coupled to the second winding.