Mixed-Domain Clocking for Imaging EMI Without Image Artifacts
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Solution Overview
Problem
Spread spectrum clocking in imaging systems, while effective in reducing electromagnetic interference (EMI), often degrades image quality due to variations in exposure and sampling times caused by the modulation of clock frequencies, leading to line-to-line intensity variations and image artifacts.
Innovation Solution
A line rate spread spectrum clock generator synchronizes the spread spectrum clock signal with the line rate of the imaging device, ensuring consistent exposure and sampling times across lines, thereby eliminating image degradation while maintaining EMI reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If spread spectrum clocking is used to reduce EMI, then electromagnetic interference is reduced, but image quality degrades due to variation in exposure time and sampling time
Solution Approach 1:
The patent divides the clocking system into two separate domains: a spread spectrum clock domain for data output timing and an unmodulated clock domain for imaging/sampling timing. This segmentation allows each domain to use the appropriate clock type for its function, resolving the contradiction between EMI reduction and image quality maintenance.
Solution Approach 2:
The patent applies different clock characteristics to different functional areas: spread spectrum modulation is applied locally to the data output clock path where EMI is the primary concern, while the imaging and sampling paths use clean unmodulated clocks where timing precision is critical. This local differentiation resolves the contradiction by optimizing each area for its primary requirement.
2Object-generated harmful factors
If spread spectrum clocking is applied to modulate clock frequency, then radiation intensity is reduced, but exposure time and processing time vary causing image degradation
Solution Approach 1:
The patent segments the timing functions by using separate clock sources: the unmodulated clock exclusively for exposure and sampling timing ensures consistent timing, while the spread spectrum clock is used only for data output timing where timing consistency is less critical. This eliminates exposure time variation while maintaining EMI reduction.
3Object-generated harmful factors
If the clock frequency is spread over a range, then the maximum radiation level is reduced, but line-to-line intensity variations occur
Solution Approach 1:
The patent applies spread spectrum modulation only to the data output clock path where EMI reduction is beneficial, while keeping the imaging and sampling clocks unmodulated to maintain timing stability. This local application resolves the contradiction by allowing frequency spreading where it helps (data output) without harming (imaging timing) the system.
Data Source
AI summary
A method of operating a line imaging device including receiving a first clock signal indicative of a system timing signal in the line imaging device, generating a second clock signal based on the first clock signal and being unmodulated where the second clock signal being used for driving the imager timing, data sampling and digitizing operations of the line imaging device, and generating a third clock signal based on the first clock signal and being modulated using a spreading waveform where the third clock signal being a spread spectrum clock signal and being used to drive the data transfer operation of the line imaging device.