Microbolometer Readout Circuit Substrate Temperature Compensation
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Solution Overview
Problem
Conventional microbolometer readout circuits face challenges in calibrating non-uniformity caused by substrate temperature variations, leading to increased power consumption, complex calibration processes, and residual non-uniformity in infrared images, especially when the substrate temperature deviates from a fixed value.
Innovation Solution
A microbolometer readout circuit with an external control circuit that includes an extraction circuit for detecting temperature variations, an analog-to-digital converter, and an image processing circuit with gain and offset digital-to-analog converters, which calibrates substrate temperature non-uniformity by heating and cooling the substrate to determine temperature compensation values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional microbolometer readout circuits use thermal-electric coolers to maintain fixed substrate temperature, then temperature stability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the temperature compensation function from the main readout circuit by introducing a separate reference pixel circuit that is thermally coupled to the substrate. This reference circuit measures substrate temperature variations independently, allowing the main imaging pixels to focus solely on detecting infrared radiation from external scenes without being burdened by temperature stabilization requirements.
Solution Approach 2:
The patent introduces a reference pixel circuit as an intermediary element that mediates between the substrate temperature variations and the imaging pixels. This reference circuit acts as a sensor that translates temperature changes into electrical signals, which are then used to compensate for the effects of temperature variations on the imaging pixels through differential measurement.
2Manufacturing precision
If two-point calibration method is used to correct space non-uniformity, then manufacturing precision is improved, but calibration process complexity and time increase
Solution Approach 1:
The patent performs preliminary calibration actions by capturing reference images at multiple temperature points (including ambient temperature and elevated temperatures) before actual imaging operations. The system pre-calculates compensation coefficients based on these reference measurements, storing them for rapid application during imaging without requiring time-consuming real-time calibration.
Solution Approach 2:
The patent changes the calibration approach from fixed two-point calibration to multi-point calibration across different temperature conditions. By capturing reference images at various temperatures (ambient, elevated, and intermediate temperatures), the system creates a more comprehensive calibration model that adapts to temperature variations, improving image uniformity across different operating conditions.
3Measurement precision
If multiple calibration points at different temperatures are used, then measurement precision is improved, but power consumption and circuit complexity increase
Solution Approach 1:
The patent implements periodic temperature variation for calibration purposes rather than maintaining continuous temperature control. The substrate temperature is periodically elevated to capture reference images at different temperature points, then returned to normal operating temperature. This periodic approach allows multi-point calibration data collection without requiring continuous power consumption for temperature maintenance.
Solution Approach 2:
The patent enables the microbolometer array to perform its own self-calibration by utilizing its inherent response to temperature variations. The reference pixel circuit automatically measures substrate temperature effects, and the image processing circuit automatically calculates and applies compensation coefficients, eliminating the need for external calibration equipment or complex control systems.
4Reliability
If reference pixel circuits are added for substrate temperature compensation, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent maintains homogeneity in the circuit design by making the reference pixel circuits structurally identical to the imaging pixels. Both types of pixels use the same microbolometer structure and readout circuitry, differing only in their thermal coupling to the substrate. This homogeneous design simplifies manufacturing and reduces overall system complexity while ensuring consistent performance characteristics.
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 simplifies the circuit structure, reduces power consumption, and effectively compensates for substrate temperature variations, reducing residual non-uniformity in infrared images without the need for thermal-electric coolers.
Implementation Method 1
An operation principle of the microbolometer is variation of resistance, when materials of the microbolometer absorb the infrared radiation, temperature of the material goes up, which generates the variation of the resistance
Implementation Method 2
If the resistance of the material decreases with the increment of the temperature, the microbolometer is called a negative temperature coefficient microbolometer; in contrast, if the resistance of the material increases with the increment of the temperature, the microbolometer is called a positive temperature coefficient microbolometer
Implementation Method 3
The extraction circuit is configured to detect a voltage signal of a temperature variation
Implementation Method 4
an analog-to-digital converter, coupled to the extraction circuit and configured to digitalize the voltage signal of the temperature variation
Implementation Method 5
the image processing circuit is configured to process the digital data to generate corrected image data in response to the substrate non-uniformity
Data Source
AI summary
A microbolometer read-out circuit includes an extraction circuit configured to detect a voltage signal of a temperature variation; an analog-to-digital converter coupled to the extraction circuit and configured to digitalize the voltage signal of the temperature variation; an image processing circuit coupled to the analog-to-digital converter; and wherein the image processing circuit is coupled to a gain digital-to-analog converter and an offset digital-to-analog converter.