Interleaved Thermopile Design for Infrared Sensor Offset Reduction
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Solution Overview
Problem
Conventional thermopile designs suffer from temperature-dependent offsets due to substrate disturbances, which are exacerbated by non-uniform substrate resistance and parasitic capacitance mismatches, leading to inaccurate infrared radiation measurements.
Innovation Solution
The thermopile structure is enhanced by interleaving thermocouples of different materials, with each leg forming a stack, creating a common mode rejection mechanism that suppresses disturbance-induced offsets through intermaterial coupling capacitance, and differential signal processing is employed to reject common-mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermopile designs are used with standard substrate structures, then manufacturing is simpler, but temperature-dependent offsets occur due to substrate disturbances and non-uniform substrate resistance
Solution Approach 1:
The thermopile is divided into multiple groups of thermocouples (first group and second group) with alternating arrangements. Each group is electrically connected in series, creating multiple parallel paths that balance substrate resistance effects and reduce temperature-dependent offsets through differential measurement.
Solution Approach 2:
Different regions of the substrate are engineered with different properties - the first and second groups of thermocouples are positioned in specific regions with controlled substrate resistance and capacitance characteristics to create local variations that compensate for overall substrate non-uniformity.
2Manufacturing precision
If thermocouples are arranged in conventional configurations, then fabrication is easier, but parasitic capacitance mismatches cause non-uniform thermocouple responses
Solution Approach 1:
The thermocouples are arranged in an asymmetric interleaved pattern where first legs of first thermocouples are physically interleaved with first legs of second thermocouples. This asymmetric arrangement creates balanced parasitic capacitance paths that equalize the electrical environment across all thermocouples, compensating for fabrication variations.
Solution Approach 2:
The thermocouples are stacked in multiple dimensions with legs interleaved in space rather than simply arranged in a single plane. This three-dimensional interleaved structure creates multiple capacitance paths that balance parasitic effects and improve response uniformity.
3Reliability
If digital signal processing circuitry is integrated close to the sensor, then signal processing is improved, but substrate disturbance signals couple back into the sensor element causing artificial offsets
Solution Approach 1:
The interleaved thermocouple structure acts as an intermediary that balances and cancels substrate disturbance signals. The differential arrangement creates common-mode rejection, where substrate disturbances appear equally in both groups and are rejected by the differential measurement circuitry.
Solution Approach 2:
The substrate disturbance signals, which would normally cause artificial offsets, are converted into useful common-mode signals that are rejected by the differential measurement system. The interleaved structure ensures that disturbances affect both groups equally, transforming them from harmful noise into cancelable common-mode signals.
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 significantly reduces or eliminates temperature-dependent offsets, improving the accuracy and reliability of infrared radiation measurements by equalizing substrate resistances and parasitic capacitances, thereby enhancing the thermopile's sensitivity and precision.
Implementation Method 1
The thermocouples yield a voltage difference at the output terminals (separate ends) when a temperature difference exists between the cold and the hot junctions
Implementation Method 2
creating a common mode rejection mechanism that suppresses disturbance-induced offsets through intermaterial coupling capacitance
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A detector (10) for responding to infrared radiation from a target, to produce a temperature indicating output signal to measurement electronics comprises a plurality of thermocouples laid out on a substrate (13). Each thermocouple comprises a first leg of a first material and a second leg of a second material, the first material being different from the second material, the first leg and the second leg being electrically connected. The plurality of thermocouples are divided into two groups, a first group (11) comprising a plurality of first thermocouples electrically connected in series, and a second group (12) comprising a plurality of second thermocouples electrically connected in series. The first group (11) and the second group (12) of thermocouples are electrically connected in series with one another at a connection point (6). The first group (11) and the second group (12) of thermocouples are supported on a common substrate (13) in close proximity to one another and at least first legs of thermocouples of the first group (11) are physically interleaved with first legs of thermocouples of the second group (12). Complete thermocouples of the two groups (11, 12) may be interleaved with one another.