Correlated Double Sampling Circuit With Feedback Anti-Blooming
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Solution Overview
Problem
Conventional detection circuits suffer from blooming phenomena when photodiodes are exposed to intense light, leading to inaccurate representation of lighting conditions due to depolarization and increased photon collection in adjacent photodiodes, which existing solutions like anti-blooming transistors are not suitable for industrial implementation.
Innovation Solution
A detection circuit with correlated double sampling and an anti-blooming circuit that compares the output voltage of the first transimpedance amplifier with a setpoint voltage from the second transimpedance amplifier, generating a negative feedback current to limit the output voltage when the difference reaches a threshold, preventing depolarization and blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If photodiode is exposed to intense light irradiation, then the current integrated in integration capacitor becomes high, but the photodiode becomes depolarized causing blooming effect on adjacent photodiodes
Solution Approach 1:
The patent implements a feedback mechanism where the voltage at the first input of the amplifier is continuously monitored and used to control the anti-blooming transistor. When the voltage drops below a threshold indicating intense light conditions, the transistor activates to prevent depolarization, creating a closed-loop feedback system that maintains photodiode reverse bias stability under varying illumination conditions.
Solution Approach 2:
The anti-blooming transistor is configured to activate before complete depolarization occurs by monitoring the voltage at the first input. This preliminary action prevents the harmful blooming effect by counteracting the depolarization trend early in the process, before it can spread to adjacent photodiodes.
2Reliability
If anti-blooming transistor is added to prevent depolarization, then blooming effect is reduced, but circuit complexity increases making industrial implementation difficult
Solution Approach 1:
The patent merges the anti-blooming function with the existing readout circuitry by integrating the anti-blooming transistor into the feedback path of the transimpedance amplifier. This consolidation allows the circuit to perform both signal amplification and blooming prevention functions simultaneously, reducing overall complexity compared to separate dedicated anti-blooming circuits.
Solution Approach 2:
The first amplifier and its associated feedback network serve multiple functions: they provide the primary transimpedance amplification function and simultaneously serve as the control mechanism for the anti-blooming transistor. This multi-functionality reduces the need for additional dedicated components, facilitating industrial implementation.
3Illumination intensity
If integration capacitor stores high current from intense light, then signal representation becomes inaccurate, but increasing capacitor size to handle higher currents increases circuit area
Solution Approach 1:
The patent employs dynamic control through the anti-blooming transistor that adjusts its conduction state based on real-time voltage conditions. This dynamic mechanism allows the integration capacitor to handle varying current levels without requiring oversizing, as the transistor actively prevents conditions that would lead to inaccurate signal representation.
Solution Approach 2:
The circuit dynamically changes the effective capacitance utilization by controlling the voltage across the integration capacitor through the anti-blooming transistor. By preventing voltage drops below the threshold, the system maintains optimal operating parameters for the capacitor, allowing accurate signal representation without requiring excessive capacitance value or physical area.
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 effectively prevents blooming by maintaining the photodiode in a reverse-biased state, ensuring accurate representation of lighting conditions and facilitating reliable industrial integration.
Implementation Method 1
a reverse biased photodiode delivers a current representative of an observed scene
Implementation Method 2
The current emitted by photodiode is integrated by integration capacitor of first integrator module
Implementation Method 3
a first transimpedance amplifier, a photodiode connected to an input of the first transimpedance amplifier
Data Source
AI summary
The detection circuit with correlated double sampling comprises two transimpedance amplifiers connected by means of a sampling capacitor. A photodiode is connected to the input of the first transimpedance amplifier. The circuit comprises an anti-blooming circuit connected between the input and output of the first transimpedance amplifier. The anti-blooming circuit comprises means for comparing the output voltage of the first transimpedance amplifier with a setpoint voltage defined by means of the output voltage of the second transimpedance amplifier. The means for comparing are connected to means for applying a feedback current to the input of the first transimpedance amplifier when the difference between the output voltage and the setpoint voltage reaches a limit value.