Image Sensor Ramp Offset Control for Glitch-Free Readout
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Solution Overview
Problem
General image sensors experience distortion in readout sensing results due to a glitch phenomenon in the ramp signal at the boundary of the most significant bit (MSB) and the least significant bit (LSB) or at some bits, affecting the accuracy of image sensing.
Innovation Solution
The image sensor incorporates a first pixel circuit, a ramp signal generator, and a ramp signal controller. The ramp signal generator provides a ramp signal that includes an offset voltage, which is controlled by the ramp signal controller. This offset voltage is applied during at least one of the reset period and the readout period to adjust the voltage range or counting result of the pixel circuit, effectively mitigating the glitch phenomenon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a general ramp signal generator is used to read out the sensing unit, then the readout process is simple and fast, but the ramp signal produces a glitch phenomenon at bit boundaries causing distortion in sensing results
Solution Approach 1:
The patent introduces a ramp signal controller as an intermediary component between the ramp signal generator and the pixel circuit. This controller generates a control signal that adjusts the ramp signal to eliminate glitches at bit boundaries, thereby removing the harmful effect while maintaining the fast readout capability
Solution Approach 2:
The patent modifies the parameters of the ramp signal by dynamically adjusting its voltage or frequency characteristics through the ramp signal controller. This parameter adjustment eliminates the glitch phenomenon at MSB-LSB boundaries while preserving the overall ramp function for accurate sensing
2Measurement precision
If the ramp signal is adjusted to eliminate glitch phenomenon, then the sensing result accuracy is improved, but the device complexity increases due to additional control circuits
Solution Approach 1:
The ramp signal controller performs multiple functions: it generates the control signal for glitch elimination, adjusts ramp signal parameters, and coordinates with the digital circuit for offset correction. This multi-functionality reduces the need for separate dedicated circuits for each function
Solution Approach 2:
The patent combines the ramp signal generation and control functions into a single integrated ramp signal controller module. This merging of functions reduces the overall circuit complexity compared to having separate glitch-free generation and parameter adjustment circuits
3Manufacturing precision
If offset voltage is applied during reset and readout periods, then the voltage range and counting result have offset improving linearity, but the control complexity increases
Solution Approach 1:
The patent applies offset voltage during the reset period before the actual readout operation. This preliminary action pre-compensates for potential non-linearity issues, simplifying the subsequent readout process and reducing the complexity of real-time correction mechanisms
Solution Approach 2:
The system uses feedback from the digital circuit to monitor the counting results and adjust the offset voltage applied during reset and readout periods. This feedback mechanism automatically maintains optimal linearity without requiring complex manual calibration or control
Data Source
AI summary
An image sensor and an operation method thereof are provided. The image sensor includes a first pixel circuit and a ramp signal generator. The first pixel circuit includes a first pixel unit; a first transfer transistor coupled to the first pixel unit and a first floating diffusion node; a first readout transistor coupled to the first floating diffusion node; a first ramp capacitor coupled to the first floating diffusion node and receiving a first ramp signal; and a first reset transistor coupled to the first floating diffusion node and receiving a reset signal. The ramp signal generator is coupled to the first ramp capacitor and configured to provide the first ramp signal. A voltage range or a counting result of the pixel circuit during at least one of a reset period and a readout period has an offset.