Bolometer Measurement Circuit with Integrator Feedback
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Solution Overview
Problem
Measurement circuits for resistive sensors, such as bolometers in infrared imagers, face challenges with sensitivity to temperature variations and precision, leading to potential saturation and technological dispersion between pixels, which affects the accuracy of infrared radiation measurement.
Innovation Solution
The proposed solution involves an alternately increasing and decreasing output signal from the integrator, using a comparator for analog-digital conversion, and a digital-analog converter that adjusts the basing current based on a second reference current, allowing for precise measurement without the need for high-precision analog-digital conversion and reducing the risk of saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-gain integrator is used to increase measurement sensitivity, then measurement precision is improved, but the circuit becomes sensitive to basing accuracy errors and risks saturation
Solution Approach 1:
The patent implements a feedback mechanism where the integrator output is fed back through a digital-to-analog converter to adjust the basing current. The system continuously monitors the integrator output and dynamically adjusts the reference current to maintain the output within the linear range, preventing saturation while preserving high gain for sensitive measurements.
Solution Approach 2:
The measurement circuit performs self-calibration by using its own output to automatically adjust its reference current. The system serves itself by detecting when the integrator output approaches saturation limits and autonomously correcting the basing current to maintain optimal operating conditions without external intervention.
2Measurement precision
If high-precision analog-to-digital conversion is implemented to improve measurement accuracy, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent replaces static high-precision ADC requirements with dynamic adjustment of the reference current. By making the basing current variable and adaptive, the system achieves high measurement accuracy through temporal dynamics rather than spatial precision, allowing the use of simpler, lower-resolution converters.
Solution Approach 2:
The system changes the operating parameters dynamically by adjusting the reference current magnitude based on the measured signal level. This parameter adaptation allows the same hardware to achieve different effective resolutions, replacing the need for fixed high-precision conversion with flexible low-precision conversion combined with parameter modulation.
3Measurement precision
If separate reference bolometers are assigned to each measurement circuit to improve measurement precision, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent makes a single reference bolometer serve multiple measurement circuits simultaneously by dynamically allocating its reference current to different channels. The shared reference element performs the compensation function for multiple bolometers through time-multiplexed or dynamically adjusted current distribution, eliminating the need for dedicated reference elements per channel.
Solution Approach 2:
The system merges multiple reference functions into a single reference bolometer by combining the reference currents algebraically. Instead of having separate reference elements for each measurement channel, the patent combines their functions into one shared element that provides reference current to multiple channels through current summing and dynamic allocation.
4Measurement precision
If temperature control elements are added to compensate for temperature variations, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent replaces mechanical/thermal temperature control systems with an electrical compensation approach. Instead of physically controlling the temperature of the reference bolometer through thermal management hardware, the system uses electrical current adjustment to achieve the same compensation effect, substituting a complex thermal control system with a simpler electrical regulation system.
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 enhances measurement precision, reduces the risk of saturation, and allows for shared reference bolometers, improving the robustness of the measurement circuit while minimizing the need for temperature regulation and reducing power consumption.
Implementation Method 1
A bolometer is a resistive element whose value varies with temperature. In a thermal imager, the respective resistances of different bolometers vary with an infrared flux from the scene being viewed.
Implementation Method 2
The resistance of the bolometer varies according to the heating, and therefore the infrared radiation received
Implementation Method 3
The resistance of the bolometer varies according to the heating
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a measurement circuit for a resistive sensor (2), comprising: an integrator (5) of information representative of the difference between a current (Ibol) passing through the sensor and a first reference current (Id); and a circuit (22, 24) for making the output of the integrator depend on a reference level (Vref5).