Anti-Eclipse Circuitry for Imager Pixel Reset Voltage Tracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional pixel architectures in semiconductor imagers suffer from eclipsing distortion, where a pixel outputs a signal corresponding to a dark pixel even when exposed to bright light, due to spillover of photogenerated charge affecting the reset voltage, requiring calibration to set an appropriate anti-eclipse threshold voltage.
Innovation Solution
An anti-eclipse circuit is implemented using modified pixel circuits on the same semiconductor substrate, forming a unity gain amplifier with one input receiving a reset signal and another set at a predetermined offset voltage, generating an anti-eclipse threshold voltage (AE_Vref) that remains stable despite fabrication variances, minimizing the need for post-manufacturing calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional pixel architecture is used, then the pixel can be manufactured with standard processes, but it suffers from eclipsing distortion where photogenerated charge spills over and affects the reset voltage, requiring additional calibration steps
Solution Approach 1:
An anti-eclipse circuit is introduced as an intermediary component between the pixel's floating diffusion node and the readout circuitry. This circuit monitors the reset voltage level and actively compensates for charge spillover effects, preventing eclipsing distortion without requiring post-manufacturing calibration. The anti-eclipse circuit acts as a mediator that isolates the pixel from the harmful effects of photogenerated charge accumulation.
Solution Approach 2:
The anti-eclipse circuit implements a feedback mechanism by continuously monitoring the voltage level at the floating diffusion node during the reset phase. When the voltage drops below a predetermined threshold (indicating charge spillover), the circuit activates to restore the voltage to the correct level. This closed-loop feedback system automatically corrects eclipsing distortion in real-time, eliminating the need for manual calibration while maintaining manufacturing simplicity.
2Reliability
If the anti-eclipse threshold voltage is set too high, then eclipsing distortion is reduced, but dark pixels may be incorrectly identified as bright pixels; if set too low, then bright light detection is improved, but eclipsing distortion increases
Solution Approach 1:
The anti-eclipse circuit employs a dynamic threshold mechanism rather than a fixed threshold voltage. The threshold is adjusted based on real-time conditions, specifically the actual reset voltage level measured during operation. This dynamic adaptation allows the circuit to maintain optimal performance across varying lighting conditions and fabrication tolerances, correctly distinguishing between dark pixels and pixels experiencing eclipsing distortion without requiring precise pre-set threshold values.
3Measurement precision
If post-manufacturing calibration is performed to set the anti-eclipse threshold, then measurement precision improves, but manufacturing time and cost increase
Solution Approach 1:
The anti-eclipse circuit is designed to be self-calibrating through its feedback mechanism. During normal operation, the circuit automatically adjusts its threshold based on the actual voltage conditions at the floating diffusion node, eliminating the need for external calibration equipment or manual adjustment steps. This self-service capability allows the pixel array to be manufactured using standard processes without additional calibration infrastructure, maintaining high manufacturing throughput while achieving accurate anti-eclipse performance.
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 anti-eclipse circuit effectively minimizes eclipsing distortion by maintaining a stable reset voltage level, ensuring accurate pixel output without extensive calibration, as it is subject to the same fabrication-induced variances as the imaging pixels.
Implementation Method 1
a light sensitive element 101, shown as a photodiode... the light sensitive element 101 is exposed to incident light and accumulates charges based on the level of the incident light
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An anti-eclipse circuit for an imager is formed from pixel circuitry over the same semiconductor substrate as the imaging pixels. More specifically, two adjacent pixel circuits are modified to form an amplifier. One input of the amplifier is adapted to receive a reset signal from one of the pixel circuits while another input is adapted to be set at a predetermined offset voltage from the output of the amplifier. The amplifier is preferably a unity gain amplifier, so that the output of the amplifier set to a voltage level equal to the predetermined offset from the voltage level of the reset signal. Accordingly, the anti-eclipse circuit outputs a reference voltage at predetermined level from the reset voltage of a pixel and does not need to be calibrated for fabrication related variances in reset voltages.