Interleaved Clock Frequency Switching for Radiated EMI Control
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Solution Overview
Problem
Current methods for controlling radiated electromagnetic interference (RE) are inadequate, as they either require additional hardware, result in minimal RE reduction, or cause display flickering due to improper frequency switching, and existing spread spectrum techniques fail to effectively distribute power across frequency bands.
Innovation Solution
The method involves a controller that determines a sequence of interleaved frequency steps within a system clock's frequency span to reduce RE, optimizing frequency changes to avoid large jumps and align with quasi peak measurement constraints, thereby reducing RE emissions without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If traditional spread spectrum techniques are used to reduce RE emissions, then RE reduction is achieved, but power is not effectively distributed across frequency bands and additional hardware may be required
Solution Approach 1:
The patent changes the frequency parameter of the clock signal dynamically by implementing a frequency switching mechanism that transitions between multiple discrete frequency steps. This parameter change approach reduces RE emissions by spreading spectral energy without requiring additional hardware components, as it utilizes software-controlled frequency modulation of the existing clock signal.
Solution Approach 2:
The patent implements dynamic frequency switching where the clock signal frequency is continuously adjusted through a sequence of frequency steps. This dynamic approach allows the system to adaptively distribute power across frequency bands, reducing peak emissions while maintaining operational functionality without adding hardware complexity.
2Object-generated harmful factors
If frequency switching is used to reduce RE, then RE reduction is achieved, but display flickering occurs due to improper frequency switching
Solution Approach 1:
The patent segments the frequency switching process into multiple discrete frequency steps rather than continuous or large jumps. By dividing the frequency transition into smaller incremental steps, the system reduces RE emissions effectively while minimizing display flickering, as each small frequency change allows the display to adapt gradually without visible artifacts.
Solution Approach 2:
The patent implements periodic frequency switching where the clock signal cycles through a predetermined sequence of frequency steps in a repeating pattern. This periodic action ensures that frequency changes occur at controlled intervals, reducing RE emissions while maintaining stable display performance by preventing irregular frequency transitions that would cause flickering.
3Productivity
If large frequency jumps are used for frequency switching, then RE reduction is achieved more quickly, but spectral amplitude of lower harmonics increases
Solution Approach 1:
The patent segments the frequency transition into multiple small incremental steps rather than executing large frequency jumps. This segmentation approach distributes the frequency change over time, reducing the spectral amplitude of lower harmonics while still achieving RE reduction. The incremental steps prevent concentrated energy at specific harmonic frequencies that would result from large abrupt frequency changes.
Data Source
Figure 1~3
Figure 2
Figure 4A~4B
AI summary
An apparatus includes a controller (102, 700) configured to be coupled to a system clock (104) that generates a clock signal for a device (106, 600) that generates radiated electromagnetic interference (RE) (108, 608). The controller is also configured to determine (201) a frequency span associated with the system clock, where the frequency span has a minimum frequency and a maximum frequency. The controller is further configured to determine (202-208) a sequence of frequency steps (300), where each frequency step is associated with a distinct frequency within the frequency span. In addition, the controller is configured to control (209) the system clock to change a frequency of the clock signal through the sequence of frequency steps in order to reduce the RE generated at or by the device. In some embodiments, the frequency steps are interleaved (208) across the frequency span to avoid large frequency jumps. In some embodiments, the frequency step duration is optimally selected to reduce quasi peak values.