Cross-Connected Capacitor Pair for ESL Reduction
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Solution Overview
Problem
Discrete capacitors in printed circuit board assemblies (PCBAs) for filtering electromagnetic interference (EMI) face reduced effectiveness at higher frequencies due to parasitic inductance from surface mounting and packaging, which increases effective series inductance (ESL) and impairs bypass filtering performance in switched mode power supplies.
Innovation Solution
A discrete field coupled capacitor with a cross-connected capacitor-pair structure, where two capacitor structures are connected in a way that their parasitic ESLs are coupled out-of-phase, reducing parasitic impedance by creating a field coupling effect that cancels out ESL impedance across specific frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete capacitors are used for EMI filtering in PCBAs, then bypass filtering is provided, but parasitic inductance from surface mounting and packaging increases effective series inductance (ESL) and reduces effectiveness at higher frequencies
Solution Approach 1:
The invention divides a single capacitor function into multiple capacitor structures (first and second capacitor structures) that are cross-connected. This segmentation allows the parasitic inductances of individual capacitors to be distributed and coupled out-of-phase, reducing the overall effective series inductance while maintaining the bypass filtering function across a broader frequency range.
Solution Approach 2:
The invention combines multiple capacitor structures into a single integrated component package with cross-connections between them. By merging multiple capacitors and their interconnections into one unified component, the design achieves lower parasitic ESL and improved high-frequency performance while simplifying PCB assembly and reducing the number of discrete components required.
2Reliability
If small value discrete capacitors are placed in parallel with larger ones to construct filter sections with lower ESL, then bypass requirements at higher frequencies are satisfied, but device complexity increases and additional series filter inductors are required
Solution Approach 1:
The invention merges multiple capacitor structures with different capacitance values into a single integrated component with internal cross-connections. This combination eliminates the need for separate parallel capacitor placements and additional series filter inductors, reducing device complexity while achieving the desired low ESL performance at high frequencies through the unified cross-connected structure.
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 solution significantly reduces parasitic ESL impedance, achieving frequency reductions of 20 to 40 dB in SMPS bypass filtering and improving power supply rejection ratio (PSRR) beyond 100 MHz, enabling more effective EMI filtering and potentially smaller, lower-cost SMPS designs.
Implementation Method 1
disposed in proximity to effect a pre-defined ESL field coupling with reverse phasing to reduce parasitic ESL
Implementation Method 2
effect a pre-defined ESL field coupling with reverse phasing to reduce parasitic ESL
Data Source
AI summary
A discrete field coupled capacitor with a cross-connected capacitor-pair, such as for use as a discrete bypass capacitor. The FCC includes a first port with first and second terminals, and a second port with third and fourth terminals. A first capacitor structure is connected between the first and second terminals, and a second capacitor structure connected between the third and fourth terminals. A cross-connect structure includes a first cross-connection to connect the first terminal to the third terminal, and a second cross-connection to connect the second terminal to the fourth terminal, to cross-connect the first and second capacitor structures. The capacitor structures have respective parasitic ESL, and can be disposed in proximity to effect a pre-defined ESL field coupling with reverse phasing to reduce parasitic ESL. The FCC can be constructed as a PCB or monolithic device. In a PCB four-layer construction, the cross-connections can be formed on respective mid-layers.