Low-Noise Sensor Clock Waveform Optimization
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Solution Overview
Problem
Current CCD sensors and driving circuits face challenges in achieving low noise and high-speed image acquisition due to signal destabilization caused by reset clock transitions, leading to suboptimal signal-to-noise ratio and accuracy, especially when detecting small defects and particles in semiconductor inspection systems.
Innovation Solution
A method and system that utilize a custom waveform generator with a phase accumulator and look-up table to minimize settling time of output signals, generating optimized clock signals that reduce noise and improve signal stability, including the use of sinusoidal waveforms and split-readout image sensors with independent clocking for each side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional reset clock waveforms are used to drive CCD sensors, then the sensor can be operated at high speed, but signal destabilization occurs causing poor signal-to-noise ratio and accuracy
Solution Approach 1:
The patent changes the waveform parameters of the clock signals from conventional square waves to sinusoidal waveforms with optimized frequency and amplitude. This parameter change reduces signal destabilization and noise coupling while maintaining high-speed operation capability, thereby improving signal accuracy and signal-to-noise ratio
Solution Approach 2:
The patent employs periodic sinusoidal clock waveforms with specific frequency characteristics to drive the CCD sensor. The periodic nature of the sinusoidal waveform allows for smooth charge transfer while minimizing abrupt transitions that cause noise, enabling both high-speed acquisition and high accuracy simultaneously
2Reliability
If multiple integrated circuits are used to generate clock signals for CCD sensors with one million or more pixels, then the sensor can be driven with proper timing, but the circuit board area increases and signals must travel long distances making noise control difficult
Solution Approach 1:
The patent merges multiple clock signal generation functions into a single integrated circuit that produces all required clock signals. This consolidation reduces the number of separate circuits needed, minimizes signal travel distances, and simplifies noise control while maintaining proper timing accuracy for driving large-scale CCD sensors
Solution Approach 2:
The patent introduces a custom waveform generator as an intermediary component that produces optimized clock signals. This intermediary uses sinusoidal waveforms to bridge the gap between digital control and analog sensor driving, improving timing accuracy while reducing noise coupling over long signal paths
3Productivity
If reset clock transitions are used to reset output voltage, then the sensor can be prepared for next pixel output, but voltage swing coupling destabilizes the output signal
Solution Approach 1:
The patent changes the reset clock waveform from a square wave with abrupt transitions to a sinusoidal waveform with smooth, continuous transitions. This parameter change eliminates voltage swing coupling and output signal destabilization while maintaining the reset function necessary for preparing the sensor for the next pixel output at high speed
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 enables high-speed image acquisition with reduced noise and improved signal stability, allowing for the detection of small defects and particles with enhanced accuracy in semiconductor inspection systems.
Implementation Method 1
The predetermined signals are generated from look-up values. The sequence of look-up values is determined by a phase accumulator.
Implementation Method 2
receiving radiation from the sample and directing received radiation to an image sensor
Data Source
AI summary
A method of inspecting a sample at high speed includes directing and focusing radiation onto a sample, and receiving radiation from the sample and directing received radiation to an image sensor. Notably, the method includes driving the image sensor with predetermined signals. The predetermined signals minimize a settling time of an output signal of the image sensor. The predetermined signals are controlled by a phase accumulator, which is used to select look-up values. The driving can further include loading an initial phase value, selecting most significant bits of the phase accumulator, and converting the look-up values to an analog signal. In one embodiment, for each cycle of a phase clock, a phase increment can be added to the phase accumulator. The driving can be performed by a custom waveform generator.