Image Link Clock Switching During Vertical Blanking to Avoid EMI
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Solution Overview
Problem
High-speed serial interfaces like MIPI can cause electro-magnetic interference (EMI) due to frequency collisions between the clock frequency and peripheral device bandwidths, leading to operational issues in image devices, especially during real-time applications like video calls or internet broadcasting.
Innovation Solution
An image device with a clock generator, link layer, detector, and frequency changer that adjusts the clock frequency during vertical blanking time to avoid frequency collisions, allowing seamless operation without resetting the phase-locked loop (PLL) circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the clock frequency is increased to achieve high-speed data transmission, then the transmission speed is improved, but frequency collision with peripheral devices occurs causing EMI
Solution Approach 1:
The clock frequency is made dynamically adjustable rather than fixed. The system can switch between different frequency values (e.g., first clock frequency and second clock frequency) based on real-time detection of frequency collision conditions, allowing the interface to adapt its transmission speed to avoid EMI while maintaining high-speed operation when possible
Solution Approach 2:
The fundamental parameter being changed is the clock frequency value. When frequency collision is detected, the system changes the clock frequency parameter from one value to another, thereby altering the transmission characteristics to avoid the harmful frequency overlap with peripheral devices while preserving the high-speed transmission capability
2Object-affected harmful factors
If the clock frequency is changed to avoid frequency collision, then EMI is reduced, but data transmission continuity may be disrupted
Solution Approach 1:
The system performs preliminary detection of frequency collision conditions and prepares for frequency switching in advance. By detecting potential EMI issues before they cause transmission failures and pre-adjusting the clock frequency during safe time periods, the system prevents disruption to data transmission continuity
Solution Approach 2:
The frequency adjustment is performed periodically during vertical blanking periods rather than continuously. These regular, scheduled frequency checks and adjustments occur during natural pauses in data transmission, ensuring that frequency changes do not disrupt active data flow while maintaining continuous operation across multiple frames
3Object-affected harmful factors
If frequency adjustment is performed during active data transmission, then EMI is avoided, but data integrity is compromised
Solution Approach 1:
Frequency adjustments are confined to periodic vertical blanking periods when no data is being transmitted. This timing strategy ensures that frequency changes occur during natural idle intervals, completely avoiding any risk to data integrity while still achieving EMI prevention through timely frequency reconfiguration
Solution Approach 2:
The system maintains continuous useful action by performing frequency adjustments only during vertical blanking periods when the display refresh cycle naturally pauses data transmission. This approach ensures uninterrupted data flow during active transmission phases while achieving continuous EMI protection through repeated periodic adjustments
Data Source
AI summary
An image device may include a clock generator to generate a first output clock of a first frequency, a link layer to generate a control signal for changing the first frequency and output first parallel data including first frame information, a detector to generate a collision avoidance command to change the first frequency to a second frequency during a vertical blanking time, and a frequency changer to receive the collision avoidance command from the detector and transmit a frequency change command to the link layer. The link layer transmits the control signal to the clock generator based on the frequency change command. The vertical blanking time is a time period from a first time point at which the first parallel data is not output from the link layer to a second time point at which second parallel data is output.