Edge Mount Connector Impedance Control via Tapered Waveguide
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Solution Overview
Problem
Existing BNC edge mount connectors fail to operate at high frequencies due to impedance mismatches and signal loss, limiting data rates to below 6 Gbps, as they cannot accurately detect and decode received signals, and prior solutions like Tsun-kit's clearance in the ground plane do not fully maintain 75 ohm characteristic impedance.
Innovation Solution
A BNC connector interface with a printed circuit board (PCB) design featuring a signal pin and outer ground terminal, where the signal pad extends under the connector pin, and a ground path with conductive vias connecting to the ground layer, along with a waveguide section and microstrip trace, maintains a smooth 75 ohm transition, reducing reflections and discontinuities, and allowing operation up to 12 Gbps or higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a BNC connector is mounted on a PCB using conventional methods, then the connector can be easily installed and connected, but impedance mismatches and signal loss occur at high frequencies, limiting operation to below 6 Gbps
Solution Approach 1:
The PCB interface is segmented into multiple functional layers: a first insulating support layer, a ground layer, a second insulating layer, and an interface layer. This segmentation allows each layer to be optimized for its specific function (mechanical support, electromagnetic shielding, insulation, and electrical connection), thereby maintaining 75 ohm impedance at high frequencies while keeping the overall structure manageable through modular construction
Solution Approach 2:
The signal path transitions from a two-dimensional surface connection to a three-dimensional multi-layer structure. The waveguide section extends vertically through multiple PCB layers, with conductive vias providing vertical electrical connections between layers. This dimensional transition allows the signal to maintain controlled impedance by utilizing the vertical space for ground references and shielding, enabling high-frequency operation up to 12 Gbps and beyond
2Reliability
If the signal pad width is increased to improve signal transmission, then impedance control is improved, but the connector pin alignment becomes more difficult
Solution Approach 1:
The interface layer features a localized signal pad structure with specific width and shape characteristics optimized for impedance control. The signal pad is positioned and dimensioned to match the connector pin geometry, creating a localized optimal connection zone. This local optimization allows the pad to maintain 75 ohm impedance while preserving precise pin alignment through proper geometric matching at the connection point
3Reliability
If ground plane clearance is added to reduce capacitance, then high frequency operation is improved, but the characteristic impedance cannot be fully maintained at 75 ohms
Solution Approach 1:
The ground layer is positioned directly beneath the signal path in the multi-layer PCB structure, creating an equipotential reference plane. This continuous ground reference maintains the electric field distribution necessary for 75 ohm characteristic impedance. The ground vias connect this ground layer to external ground terminals, ensuring the entire signal path has a stable reference potential, thereby maintaining impedance control while enabling high-frequency 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 enables seamless signal transmission at high frequencies by minimizing impedance mismatch and insertion loss, allowing data rates up to 12 Gbps and beyond, meeting eye mask requirements and reducing bit error rates.
Implementation Method 1
maintains a smooth 75 ohm transition, reducing reflections and discontinuities
Implementation Method 2
The waveguide section electrically connects to the signal pad such that the waveguide section is formed at a first end with the signal pad width and then tapering to a second end having a second width
Implementation Method 3
The ground path is formed on each side of the signal path and includes conductive vias that pass through the second insulating layer to electrically connect the ground path to the ground layer in the PCB
Implementation Method 4
the waveguide section is formed at a first end with the signal pad width and then tapering to a second end having a second width
Data Source
AI summary
An electrical interface on a circuit board is disclosed for electrically connecting the circuit board to a connector to reduce reflections and impedance mismatch and increase power transfer from the connector to the signal path of the circuit board. The signal interface includes a signal conductor including a signal pad configured to connect to a connector pin and a waveguide section extending from the signal pad. The waveguide narrows from a signal pad width to connect to a microstrip conductor. A first ground section is spaced rightward from the signal conductor such that the inner edge of the first ground section, angles in correspondence with the narrowing of the waveguide to generally track an outer right edge of the waveguide. A second ground section is spaced leftward from the signal conductor and configured generally similarly to the first ground section.