Planar Audio Amplifier Inductor with Integrated Sense Coil
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Solution Overview
Problem
Conventional audio amplifiers with wound magnetic structures face issues such as coupling capacitance, difficulty in tuning due to magnetic coupling coefficients, additional costs from extra windings and pins, and mechanical variability, which affect the accuracy of current sensing in class D amplifiers.
Innovation Solution
A planar audio amplifier output inductor with a ferrite core structure and separate windings on different circuit board layers, utilizing a spacing structure with dielectric material and interconnect pins to achieve a repeatable coupling coefficient, and incorporating a sense coil for current sensing, which reduces parasitic capacitance and enhances inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wound magnetic structures are used in audio amplifiers, then inductance can be achieved, but coupling capacitance increases and current sensing accuracy deteriorates
Solution Approach 1:
The inductor is divided into multiple planar windings arranged in a segmented configuration on circuit board layers, replacing the conventional wound structure. This segmentation reduces coupling capacitance between windings and enables separate sense coil placement for accurate current sensing without interference from parasitic capacitance.
Solution Approach 2:
The inductor transitions from a three-dimensional wound magnetic structure to a two-dimensional planar structure fabricated on circuit board layers. This dimensional change eliminates the complex inter-winding capacitance of traditional coils while maintaining inductance through optimized planar geometry and ferrite core integration.
2Manufacturing precision
If magnetic coupling coefficients are adjusted for tuning, then inductance can be optimized, but mechanical variability increases
Solution Approach 1:
The mechanical adjustment of magnetic coupling coefficients is replaced by electrical design parameters in the planar structure. The coupling coefficient is determined by fixed geometric relationships between planar windings and ferrite core dimensions, eliminating mechanical variability while enabling precise inductance control through PCB layout and material selection.
3Measurement precision
If extra windings and pins are added for current sensing, then sensing capability is improved, but device complexity and cost increase
Solution Approach 1:
The current sense coil is integrated into the same planar circuit board structure as the main inductor windings, sharing the same fabrication process and substrate. This merging eliminates the need for separate windings and additional pins, reducing device complexity while providing accurate current sensing through the planar sense coil.
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 planar inductor design provides a stable and repeatable coupling coefficient, reducing parasitic capacitance and mechanical variability, thereby improving the accuracy of current sensing and system response in class D amplifiers.
Implementation Method 1
a ferrite core structure substantially enclosing the first plurality of windings and the second plurality of windings
Implementation Method 2
a sense coil, sensing the current in the inductor, formed on a layer of the first circuit board
Data Source
Figure 1~3
Figure 2
Figure 4A~4B
AI summary
An audio amplifier, that includes a planar inductor structure that includes a first plurality of windings, formed on layers of a first circuit board and a second plurality of windings, formed on layers of a second circuit board. The planar inductor structure may further include a sense winding.