PCB Distributed Capacitance for Radiated Emission Reduction
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Solution Overview
Problem
High-speed computational devices generate excessive high-frequency electromagnetic radiation due to short rise and fall times of digital signals, which is difficult to attenuate using conventional low pass filters, especially when rise and fall times are very short, leading to unacceptably high frequency energy emission.
Innovation Solution
Embedding local regions of distributed capacitance adjacent to conductive traces on printed circuit boards acts as a low pass filter, increasing rise and fall times without degrading signal characteristics or inducing timing jitter, using electrically isolated metallic structures that operate as capacitors to reroute high-frequency currents back to their source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If computational devices operate at high processing speeds with short rise and fall times, then productivity increases, but high frequency electromagnetic radiation emissions increase
Solution Approach 1:
The patent introduces an intermediary structure (the capacitive element coupled to the conductive trace) that mediates between the high-speed digital signal and the electromagnetic radiation emission. This intermediary captures high-frequency voltage oscillations and redirects them, preventing radiation without significantly affecting the signal's rise and fall times or processing speed.
Solution Approach 2:
The patent changes the electrical parameters of the conductive trace by adding a capacitive element, which modifies the voltage oscillation characteristics. This parameter change (adding capacitance) selectively attenuates high-frequency radiation while preserving the signal integrity and timing characteristics needed for high-speed operation.
2Object-generated harmful factors
If conventional low pass filters are used to increase rise and fall times, then electromagnetic radiation is reduced, but signal characteristics are degraded and timing jitter is induced
Solution Approach 1:
Instead of applying a global low pass filter that degrades the entire signal, the patent applies a localized capacitive element at a specific position along the conductive trace. This local modification selectively targets high-frequency radiation without affecting the overall signal characteristics or introducing timing jitter.
Solution Approach 2:
Rather than using a conventional low pass filter that increases rise and fall times to reduce radiation, the patent inverts the approach by adding capacitance that selectively suppresses high-frequency oscillations while maintaining the original signal timing characteristics, thus reducing radiation without degrading signal quality.
3Object-generated harmful factors
If discrete capacitor components are used for filtering, then high frequency radiation is reduced, but parasitic effects occur above 25-30 megahertz
Solution Approach 1:
The patent extracts the capacitive function from a discrete capacitor component and integrates it directly into the PCB structure as a capacitive element formed by conductive patterns on the board. This eliminates the parasitic effects associated with discrete capacitors while maintaining the filtering function at high frequencies.
Solution Approach 2:
The patent creates a composite structure by integrating the capacitive element directly into the PCB substrate, combining the trace conductor and capacitor in a single integrated structure. This composite approach eliminates the parasitic inductance of discrete components and enables effective high-frequency radiation reduction.
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
Effectively attenuates high-frequency electromagnetic radiation emissions from computational devices without affecting voltage amplitude or bit period, reducing radiated energy while maintaining system synchronization.
Implementation Method 1
local regions of distributed capacitance are embedded within printed circuit boards (PCBs) adjacent the PCB conductive traces
Implementation Method 2
The local regions of capacitance act as low pass filters and thus increase the rise and/or fall times occurring on such adjacent traces
Implementation Method 3
the voltage changes associated with the rise and fall times of the waveforms of bits transmitted along such traces can radiate high frequency electromagnetic radiation
Implementation Method 4
electrically isolated metallic structures that operate as capacitors to reroute high-frequency currents back to their source
Data Source
AI summary
A method and system for reducing the release of high frequency electromagnetic energy into the environment is disclosed, wherein local regions of distributed capacitance are embedded within a printed circuit board (PCB) and adjacent the PCB conductive traces act as low pass filters and thus increase the rise and/or fall times occurring on such traces. The present invention increases very short rise and/or fall times (e.g., 200 picoseconds or less) without degrading or detrimentally affecting other signal characteristics. The present invention does not substantially affect the voltage amplitude and does not affect the bit period when lengthening the rise and/or fall time. Also, the present invention does not induce any timing jitter that may cause synchronization problems within the system.