Spread Spectrum Clock Signal for Gaming Machine EMI Reduction
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Solution Overview
Problem
Modern gaming machines experience excessive electromagnetic interference (EMI) due to long light buses carrying clock signals, which can interfere with other carrier signals and devices, and existing solutions to reduce EM emissions, such as shielding and ferrite clamps, increase system costs and are often not reliably maintained.
Innovation Solution
Implementing a digital spread spectrum technique by generating a spread spectrum clock signal that jitter's between two or more frequencies around the fundamental frequency, reducing EM emissions by distributing peak power across multiple frequencies and their harmonics, using a programmable logic device like a FPGA or CPLD to manage the clock signal and synchronize data signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional clock signals are used on long light buses, then synchronous data transmission is achieved, but electromagnetic emissions increase causing interference with other carrier signals and devices
Solution Approach 1:
The patent applies dynamics by making the clock signal frequency variable rather than fixed. The spread spectrum technique modulates the clock signal to vary its frequency over time, causing the electromagnetic energy to be distributed across a range of frequencies rather than concentrated at a single frequency. This dynamic frequency variation reduces peak emissions while maintaining synchronous data transmission capability.
Solution Approach 2:
The patent changes the frequency parameter of the clock signal from a constant value to a varying value across a spectrum. By spreading the clock signal's frequency content over multiple frequencies through modulation techniques, the electromagnetic emissions are distributed and reduced at any single frequency point, thereby reducing interference while preserving transmission functionality.
2Object-generated harmful factors
If shielding components and ferrite clamps are added to reduce EM emissions, then electromagnetic interference is reduced, but system cost increases due to added material, manufacturing, and labor costs
Solution Approach 1:
The patent replaces physical electromagnetic shielding mechanisms (mechanical/system-level solutions like shields and ferrite clamps) with an electrical signal processing solution. Instead of adding physical barriers to block emissions, the invention modifies the electrical clock signal itself to inherently reduce emissions, eliminating the need for additional shielding components and associated costs.
Solution Approach 2:
The patent extracts the harmful electromagnetic emissions characteristic from the clock signal by transforming its frequency distribution. Rather than trying to contain or block the emissions physically, the solution extracts the concentrated frequency energy and redistributes it across a spectrum, effectively removing the harmful peak emissions without adding physical components.
3Object-generated harmful factors
If shielding components and ferrite clamps are used to lower emissions, then EM emission levels are reduced, but these remedies are not reliably replaced after system field maintenance because leaving them out has no detrimental effect on functional operation
Solution Approach 1:
The patent implements self-service by integrating the emission reduction functionality directly into the clock signal generation process. The spread spectrum technique is built into the signal source itself, making the emission control inherent to the system's operation rather than a separate removable component. This ensures that maintenance personnel cannot inadvertently remove or disable the emission reduction feature without affecting system functionality.
Data Source
AI summary
Techniques for reducing electromagnetic (EM) emission in a wager-based gaming machine. A gaming machine includes one or more processors configured to generate a bus clock signal having a fundamental frequency and fundamental spectral components at harmonics of the fundamental frequency. The fundamental spectral components each have a fundamental amplitude. A signal processor is configured to generate a spread spectrum clock signal having a nominal frequency substantially equivalent to the fundamental frequency of the bus clock signal as well as nominal spectral components at harmonics of the nominal frequency. However, the nominal spectral components each have a nominal amplitude less than the fundamental amplitude of a fundamental spectral component at the same harmonic. A bus connects the signal processor with one or more elements and carries the spread spectrum clock signal to the one or more elements, thereby reducing EM emissions from the bus.