Imaging Signal Comparator Layout for Parasitic Capacitance Errors
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Solution Overview
Problem
Existing signal processing devices for image sensors face challenges in reducing circuit area and cost while maintaining accurate analog-to-digital (A/D) conversion, particularly due to parasitic capacitance issues that lead to errors in correlated double sampling results.
Innovation Solution
A signal processing device with a comparison unit, selection unit, and switching unit that maintains a consistent signal level across multiple comparison processes, using a signal line with parasitic capacitance between the input terminal and the floating node, to reduce coupling voltage fluctuations and errors without increasing circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If circuit miniaturization is performed to reduce size and power consumption, then device size and power consumption are reduced, but parasitic capacitance increases causing coupling errors in A/D conversion
Solution Approach 1:
The signal line in the selection unit is configured to transmit signals at the same potential level throughout multiple comparison processes. This equipotential configuration ensures that the parasitic capacitance between the signal line and the floating node does not cause voltage fluctuations or coupling errors, thereby maintaining A/D conversion accuracy despite circuit miniaturization
Solution Approach 2:
The invention changes the signal level parameter in the selection unit's signal line to maintain consistency across different comparison processes. By keeping the signal at the same level (e.g., always at reference potential), the parasitic capacitance effect is neutralized, preventing coupling errors while allowing compact circuit design
2Measurement precision
If shield wiring or increased wiring distance is used to reduce parasitic capacitance effects, then A/D conversion accuracy is improved, but circuit area increases and cost increases
Solution Approach 1:
Instead of physically separating wirings or adding shields, the invention changes the electrical parameter (signal level) in the selection unit's signal line to match the floating node's potential. This parameter adjustment eliminates the voltage difference that would otherwise cause coupling through parasitic capacitance, achieving accurate A/D conversion without increasing circuit area
3Area of moving object
If control circuit is placed near pixel array for miniaturization, then circuit area is reduced, but parasitic capacitance between control wiring and comparison input terminal increases causing coupling errors
Solution Approach 1:
The signal line connecting the selection unit (control circuit) to the comparison unit is maintained at the same potential level as the floating node throughout the comparison processes. This equipotential arrangement ensures that even though the control circuit is placed near the pixel array for miniaturization, the parasitic capacitance does not cause coupling errors that would affect correlated double sampling accuracy
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 approach enables accurate A/D conversion with reduced development and manufacturing costs by minimizing circuit area and power consumption, while maintaining high-speed processing and gradation enhancement.
Implementation Method 1
the selection unit includes a signal line in which a parasitic capacitance is caused between the signal line and the floating node as the input terminal of the comparison unit
Data Source
AI summary
A signal processing device includes a comparison unit to compare a signal level of an analog signal with a signal level of a reference signal; a selection unit configured to select the reference signal to be supplied to the comparison unit; and a switching unit capable of switching a signal line connected to an input terminal of the comparison unit such that a signal line via which the selected reference signal is transmitted is connected to the input terminal of the comparison unit, wherein the comparison unit includes a floating node as the input terminal, the selection unit includes a signal line in which a parasitic capacitance is caused between the signal line and the floating node as the input terminal of the comparison unit, and the signal line of the selection unit is configured to transmit an identical level of signal in multiple comparison processes of the comparison unit.