Dynamic Pedestal Level Adjustment in Image Sensors
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Solution Overview
Problem
Image sensors face challenges in managing dark current, leading to pedestal level issues that result in wasted digital codes and increased quantization noise due to fixed pedestal levels that do not adapt to varying operating conditions.
Innovation Solution
A dynamic adjustment of the pedestal level based on operating conditions, such as temperature, gain, and integration period, using a processor to determine the expected distribution of dark current and adjust the pedestal level, thereby minimizing unused digital codes and reducing variance in pixel signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed pedestal level is used to prevent pixel signals from clipping at zero, then the minimum digital code value is preserved, but digital codes are wasted and quantization noise increases when dark current is low
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed pedestal level to a dynamically adjusted pedestal level that changes based on operating conditions. The processor determines an adjusted pedestal level based on temperature, integration period, and gain, allowing the system to adapt the pedestal level to match actual dark current conditions, thereby preventing code waste while maintaining signal integrity.
Solution Approach 2:
The patent changes the parameter of pedestal level from a fixed value to a variable value that depends on operating conditions. By adjusting the pedestal level parameter based on temperature, integration period, and gain settings, the system optimizes the use of digital codes across different operating scenarios, reducing quantization noise and preventing clipping.
2Reliability
If a higher pedestal level is used to account for worst-case dark current conditions, then pixel signals are protected from clipping, but the meaningful signal is supported by fewer digital codes
Solution Approach 1:
The system dynamically adjusts the pedestal level based on actual operating conditions rather than using a fixed high value. The processor calculates the appropriate pedestal level based on temperature, integration period, and gain, allowing the signal support range to expand when dark current is low while maintaining protection against clipping when dark current is high.
Solution Approach 2:
The pedestal level parameter is changed from a static high value to a dynamic value that adapts to operating conditions. This allows the system to optimize the digital code range for signal representation based on actual dark current levels, improving measurement precision when conditions permit while maintaining reliability when needed.
3Loss of substance
If the pedestal level is reduced to minimize unused digital codes, then quantization noise decreases, but pixel signals may clip at zero
Solution Approach 1:
The system dynamically determines the optimal pedestal level by analyzing operating conditions (temperature, integration period, gain) in real-time. This dynamic adjustment ensures that the pedestal level is low enough to minimize unused codes and quantization noise when dark current is low, while being high enough to prevent clipping when dark current is high.
Solution Approach 2:
The system uses feedback from operating condition parameters (temperature sensors, integration period settings, gain values) to determine the appropriate pedestal level. This feedback mechanism allows the system to continuously optimize the pedestal level to balance between preventing clipping and minimizing code waste, rather than using a fixed conservative value.
Data Source
AI summary
A pedestal level for an image sensor can be dynamically adjusted based on one or more parameters. The parameters include one or more operating conditions associated with the image sensor, pre-determined image sensor characterization data, the number of unused digital codes, and/or the number of clipped pixel signals. The operating conditions can include the temperature of the image sensor, the gain of at least one amplifier included in processing circuitry operably connected to at least one pixel, and/or the length of the integration period for at least one pixel in the image sensor. Based on the one or more of the parameters, the pedestal level is adjusted to reduce a number of unused digital codes in a distribution of dark current. Additionally or alternatively, the variance of the pixel signals can be reduced to permit the use of a lower pedestal level.