Low Flux Detection Circuit with Charge Transfer Stabilization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optic detection circuits face challenges in achieving a high signal-to-noise ratio and linearity in converting light signals to electric signals, especially under low light flux conditions, due to stray photon emission and fluctuations in bias conditions, which impair the integrity and amplitude of the signal.
Innovation Solution
A detection circuit with a stray capacitor and a bias circuit that switches between reverse bias and floating states, using a transfer circuit to stabilize the integration node potential by transferring charges from the stray capacitor to an integration capacitor, maintaining the bias conditions and improving signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the photodetector is left at a floating potential during charge integration, then the circuit complexity is reduced and power consumption is lowered, but the bias conditions fluctuate which impairs signal integrity and linearity
Solution Approach 1:
The patent divides the integration capacitor into two separate capacitors: a first integration capacitor connected to the photodetector and a second integration capacitor connected to the readout circuit. This segmentation allows the photodetector to be reset to a fixed potential while maintaining charge integration, thus preserving signal integrity without requiring complex biasing circuits.
Solution Approach 2:
The patent introduces a charge transfer mechanism as an intermediary between the photodetector and the readout circuit. Charges are first accumulated on the first integration capacitor connected to the photodetector, then transferred to the second integration capacitor connected to the readout circuit. This intermediary approach allows the photodetector to be reset while preserving the accumulated charge information, maintaining signal integrity with simpler circuitry.
2Power
If the integration capacitor charges progressively during signal detection, then the signal amplitude increases, but the bias potential varies which degrades linearity and signal-to-noise ratio
Solution Approach 1:
By segmenting the integration capacitor into two separate capacitors, the patent enables the photodetector side to be reset to a fixed potential while the readout circuit side accumulates charges. This maintains a stable bias potential at the photodetector during the entire integration process, ensuring linearity and high signal-to-noise ratio while still achieving signal amplification through charge accumulation on the second capacitor.
Solution Approach 2:
The patent performs preliminary reset of the photodetector to a fixed potential before charge integration begins. This preliminary action establishes stable bias conditions that are maintained throughout the integration process, ensuring linearity is preserved while charges are accumulated on the first integration capacitor and subsequently transferred to the second capacitor for signal amplification.
3Measurement precision
If an operational amplifier is used for signal integration and biasing, then the signal-to-noise ratio improves for medium or weak signals, but the circuit size and power consumption increase
Solution Approach 1:
The patent extracts the operational amplifier from the pixel-level detection circuit and relocates it to a post-processing stage. At the pixel level, only simple charge transfer transistors and capacitors are used, minimizing circuit size. The operational amplifier is applied later to the transferred voltage signal to achieve low-noise amplification and integration, thus improving signal-to-noise ratio without increasing the area of the detection circuit.
Solution Approach 2:
The patent separates the detection function from the amplification/integration function in terms of spatial dimension. The detection circuit at the pixel level is kept minimal in size, while the amplification and integration operations are performed in a different dimension (post-processing stage) where larger circuit elements like operational amplifiers can be used without constraining the detector area.
4Stability of the object's composition
If the photodetector is reset to a fixed potential during integration, then bias stability is improved, but charge accumulation cannot be performed
Solution Approach 1:
The patent segments the integration function into two stages using two separate capacitors. The first capacitor is connected to the photodetector and allows charge accumulation while the photodetector is reset to a fixed potential. The second capacitor is connected to the readout circuit and receives the accumulated charges through a transfer mechanism. This segmentation enables both bias stability at the photodetector and charge accumulation to coexist.
Solution Approach 2:
The patent introduces a charge transfer mechanism as an intermediary that decouples the photodetector biasing from the charge accumulation process. The photodetector is reset to a fixed potential, charges accumulate on the first integration capacitor, then the intermediary transfer mechanism moves these charges to the second integration capacitor connected to the readout circuit. This allows bias stability and charge accumulation to be achieved simultaneously by separating them in time and space.
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
This configuration enhances the correlation between the optic signal and the electric signal, reducing noise and maintaining signal integrity by stabilizing the bias conditions, thus improving the signal-to-noise ratio and linearity, particularly beneficial for low flux detectors like those in the LWIR band.
Implementation Method 1
the incident radiation is converted into a quantity of electrons which is representative of the observed scene
Data Source
AI summary
The detection circuit comprises a detector connected to an integration node. A bias circuit biases the detector between a first bias state and a second floating state. The potential of the integration node is at a target value when the bias circuit biases the detector to the first state and varies when the detector is in floating state. A measurement circuit without charge losses delivers a value representative of the potential present on the integration node N. A transfer circuit of the electric charges performs transfer of the electric charges from a stray capacitor of the photodiode to an integration capacitor. An output terminal delivers a voltage representative of the potential present on the second terminal of the first capacitor.