Image Reading Apparatus Clock Signal Fluctuation Cancellation
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Solution Overview
Problem
High picture element density and operating speed in image reading apparatuses lead to increased undesired electromagnetic radiation and fluctuations in the output voltage of Charge-Coupled Devices (CCDs), resulting in image signal level fluctuations and horizontal streaks in scanned images due to frequency modulation of clock signals.
Innovation Solution
A novel image reading apparatus that includes a photoelectric converter driven by a frequency modulated clock signal, an overlapping circuit to cancel the fluctuations in the analog image signal with an anti-phase signal, and an analog digital converter to produce a stable digital output, effectively eliminating the fluctuation component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the clock signal frequency is increased to drive the CCD and signal processing IC at higher speeds, then the operating speed and picture element density are improved, but undesired electromagnetic radiation increases
Solution Approach 1:
The patent applies spread spectrum clock generation that periodically modulates the clock signal frequency according to a pseudo-random code sequence. This periodic frequency modulation spreads the concentrated electromagnetic energy across a broader frequency spectrum, reducing peak radiation levels while maintaining the required operating speed for high picture element density
2Object-generated harmful factors
If frequency modulation is applied to reduce electromagnetic radiation, then undesired radiation is reduced, but the output offset voltage of the CCD fluctuates causing image signal level variations
Solution Approach 1:
The patent employs a feedback mechanism where the frequency modulated clock signal is monitored and the resulting CCD output offset voltage fluctuations are detected. A correction circuit then applies compensating signals to counteract these fluctuations, ensuring that image signal levels remain consistent across all scanned lines despite the frequency modulation used to reduce electromagnetic radiation
3Object-generated harmful factors
If the clock frequency is modulated to spread spectrum characteristics, then electric field strength at frequency peaks is reduced, but horizontal streaks appear in scanned images due to periodic frequency fluctuations
Solution Approach 1:
The patent introduces an intermediary correction circuit between the frequency modulated clock signal and the CCD output. This intermediary circuit generates compensating signals that are superimposed on the image signal to cancel out the periodic fluctuations caused by clock frequency modulation, thereby eliminating horizontal streaks while preserving the spread spectrum benefits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution stabilizes the image signal output, eliminating horizontal streaks and ensuring consistent image quality by canceling the fluctuation component caused by clock frequency modulation, thereby improving the image reading process.
Implementation Method 1
a photoelectric converter that converts incident light into an analog image signal
Data Source
AI summary
An image reading apparatus and an image forming apparatus including the image reading apparatus. The image reading apparatus includes a photoelectric converter to convert incident light into an analog image signal, a drive unit to drive the photoelectric converter by a frequency modulated clock signal, an overlapping circuit to overlap an anti-phase analog signal to the analog image signal fluctuating according to the frequency modulated clock signal with a same amount of fluctuation as that of the analog image signal, and an analog digital converter to convert the overlapped analog image signal into a digital output.