Clock Phase Diffusion for EMI Reduction Without Display Flicker
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Solution Overview
Problem
Conventional clock frequency diffusing devices cause variations in display luminance and non-uniformity, such as flicker, in passive type organic display devices due to frequency variations in the output clock signal, leading to significant luminance variations and electromagnetic interference (EMI) from harmonics.
Innovation Solution
A clock frequency diffusing device that generates phase-different clock signals and randomly selects among them using a random number generator to produce a diffused frequency output clock signal, reducing harmonics and stabilizing the frame frequency and on/off ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If frequency diffusion is applied to reduce EMI, then electromagnetic interference is reduced, but display luminance uniformity deteriorates due to variations in frame frequency and on/off ratio
Solution Approach 1:
The patent applies parameter changes by carefully controlling the frequency diffusion range to be within ±5% of the center frequency. This limited parameter variation reduces EMI through frequency spreading while maintaining stable frame frequency and on/off ratio for consistent display luminance. The voltage control signal is constrained within specific bounds (Vmin to Vmax) to achieve this balance.
Solution Approach 2:
The patent implements dynamic frequency adjustment where the output clock frequency varies over time within a controlled range. The voltage DAC dynamically adjusts the control voltage based on diffused data, creating a dynamically varying frequency that reduces EMI peaks while the variation is bounded to maintain display performance. This dynamic approach allows the system to adapt frequency to reduce interference without compromising stability.
2Object-affected harmful factors
If conventional frequency diffusion is used, then EMI is reduced, but harmonics remain significant causing residual interference
Solution Approach 1:
The patent employs periodic action through the up-down counter that generates monotonously increasing and decreasing data patterns. This periodic waveform generation, when converted to voltage and frequency, creates a diffused spectrum that spreads energy across frequencies while the structured periodic nature helps minimize harmonic peaks compared to random diffusion methods.
Solution Approach 2:
The patent converts the potentially harmful sharp spectral peaks into beneficial spread spectrum characteristics. By using the up-down counter to generate a triangular-like waveform pattern rather than random noise, the energy is dispersed in a controlled manner that reduces peak harmonics while maintaining the frequency diffusion benefit for EMI reduction.
3Object-affected harmful factors
If frequency diffusion width is increased to reduce EMI, then electromagnetic interference is suppressed, but frame frequency variation increases causing display non-uniformity
Solution Approach 1:
The patent optimizes the frequency diffusion parameter by limiting the diffusion width to ±5% of the center frequency. This parameter setting achieves sufficient EMI suppression while keeping frame frequency variation within acceptable bounds for stable display operation. The voltage range (Vmin to Vmax) is carefully selected to correspond to this optimal frequency spread.
4Object-affected harmful factors
If random number generation is used for frequency diffusion, then EMI is reduced, but errors in integration occur and luminance variations increase
Solution Approach 1:
The patent replaces random number generation with periodic up-down counter operation that produces monotonously increasing and decreasing data. This periodic action eliminates the integration errors associated with random sequences while still achieving frequency diffusion. The structured waveform ensures consistent, predictable frequency variation that maintains display precision.
Data Source
AI summary
A clock frequency diffusing device including a multiphase clock signal generator, a random number generator, signal selectors, and a clock signal generator. The multiphase clock signal generator receives an input clock signal and produces a plurality of delayed clock signals that are delayed relative to the input clock signal by various amounts of time. The clock signal selector randomly chooses one of the delayed signals based upon random numbers generated by the random number generator and produces a selector output signal based on its chosen delayed clock signal. A clock signal generator receives the selector output signal and produces an output clock signal.