CMOS Image Sensor Gain Adjustment via Adjustable RC Time Constant
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Solution Overview
Problem
CMOS image capture devices face yield reduction due to process variations affecting the formation of resistors and capacitors, leading to inconsistent gain characteristics.
Innovation Solution
Incorporating a self-adjustable ramp signal generator with an adjustable RC time constant, utilizing a resistor or capacitor array and a multiplexer to adjust the resistance or capacitance in response to a control signal, allowing the device to adjust its gain characteristics independently through a test ADC and digital signal controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed resistor and capacitor values are used in the ramp signal generator, then the device structure is simple, but the gain characteristics become inconsistent due to process variations
Solution Approach 1:
The patent applies dynamics by making the resistor and capacitor values adjustable rather than fixed. The ramp signal generator uses switchable resistor arrays and capacitor arrays that can dynamically change their resistance and capacitance values based on feedback from the ADC, allowing the system to adapt to process variations and maintain consistent gain characteristics.
Solution Approach 2:
The patent changes the parameters of the resistor and capacitor in the ramp signal generator based on measured ADC performance. By adjusting the resistance and capacitance values according to feedback from the ADC's digital output, the system optimizes the ramp signal characteristics to compensate for manufacturing variations and ensure consistent gain across devices.
2Productivity
If process margins are insufficient, then manufacturing is faster and cheaper, but the resistor and capacitor formation becomes highly variable
Solution Approach 1:
The patent implements feedback by using the digital output from the ADC to measure the actual performance of the ramp signal generator, then feeding this information back to adjust the resistor and capacitor values. This closed-loop system compensates for manufacturing variations without requiring tighter process control, allowing fast and cost-effective manufacturing while maintaining precision through post-fabrication adjustment.
Solution Approach 2:
The system performs self-adjustment by automatically measuring its own performance through the ADC and correcting its own parameters by switching to appropriate resistor and capacitor values. This self-service capability eliminates the need for external calibration equipment or manual adjustment, making the manufacturing process more efficient while ensuring precision.
3Reliability
If the ramp signal voltage is adjusted to compensate for process variations, then gain characteristics improve, but additional control circuitry is required
Solution Approach 1:
The patent makes the existing control circuitry multi-functional by having it perform both its original function of generating the ramp signal and the additional function of adjusting the resistor and capacitor values based on ADC feedback. The same control logic that generates the ramp signal also controls the switches that adjust the resistance and capacitance, eliminating the need for separate adjustment circuitry and reducing overall device complexity.
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 the CMOS image capture device to self-adjust its gain characteristics, ensuring they remain within predetermined specifications, thereby enhancing device yield and reliability.
Implementation Method 1
The operational amplifier integrates an input signal Vin from an external source using a resistance of the resistor 211 and a capacitance of the capacitor 221 and outputs the integrated value as the ramp signal Vramp
Implementation Method 2
CMOS image photographing devices convert optical signals, which are input when a subject is photographed, into digital signals
Data Source
AI summary
A CMOS image capture device includes an array of pixel elements configured to convert an image received as light at a surface thereof into analog output signals. An image processing circuit is also provided. The image processing circuit is configured to generate digital output signals from which the image can be recreated in response to the analog output signals. The image processing circuit has self-adjustable gain characteristics. The image processing circuit includes a ramp signal generator having an integration circuit therein with an adjustable RC time constant. The integration circuit includes an operational amplifier and a resistor array and/or a capacitor array electrically coupled to the operational amplifier. This resistor array and/or capacitor array enables the adjustable RC time constant.