Pin-Compatible Infrared Detector with Transimpedance Amplifier
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Solution Overview
Problem
Conventional pyroelectric infrared sensors experience high electric time constants and lack thermal stability when subjected to thermal shocks or vibrations, leading to prolonged downtime and sensitivity issues, and are not pin-compatible with transimpedance amplifiers, requiring costly modifications to readout devices.
Innovation Solution
A pin-compatible infrared light detector with a transimpedance amplifier configuration, utilizing a pyroelectric sensor chip and an asymmetric operational amplifier with a voltage divider and negative feedback components, allowing direct integration with conventional voltage-mode signal processing circuits and enhancing thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a source follow circuit with high impedance resistor is used to read pyroelectric infrared sensors, then the sensor can be read and amplified, but the electric time constant becomes very large leading to long downtime during thermal shocks or vibrations
Solution Approach 1:
The patent replaces the conventional source follow circuit (which uses high impedance resistors and junction-gate field effect transistors) with a transimpedance amplifier circuit. This substitution fundamentally changes how the sensor signal is read, converting the high-impedance voltage-mode reading into a low-impedance current-mode reading, thereby reducing the electric time constant from seconds to milliseconds and eliminating the long downtime during thermal shocks or vibrations.
Solution Approach 2:
The patent changes the operating parameters of the readout circuit by introducing a transimpedance amplifier with specific resistor values (R1 and R2) that set the gain and input impedance. This parameter change transforms the electric time constant from a large value (R*Cpixel in source follow mode) to a small value determined by the amplifier's feedback resistor, thereby reducing downtime while maintaining thermal stability.
2Loss of time
If a transimpedance amplifier is used to amplify sensor charges, then the electric time constant is reduced, but the output signal becomes incompatible with downstream voltage-mode readout devices requiring costly modifications
Solution Approach 1:
The patent introduces a voltage divider circuit with resistors R3 and R4 as an intermediary between the transimpedance amplifier output and the downstream readout device. This voltage divider converts the amplifier's output signal into a compatible voltage format while maintaining the low-impedance characteristics, thereby enabling pin-compatible operation with existing voltage-mode readout devices without requiring costly modifications to the downstream circuitry.
Solution Approach 2:
The patent designs the readout circuit to be universally compatible with both transimpedance amplifier outputs and conventional voltage-mode readout devices. By incorporating the voltage divider interface, the circuit can accommodate different sensor types and readout configurations, making the system versatile and eliminating the need for costly modifications when swapping sensors or integrating with existing equipment.
3Device complexity
If conventional pyroelectric sensors are used with source follow circuits, then the circuit can be simple, but the device lacks sensitivity to thermal shocks and vibrations due to high electric time constant
Solution Approach 1:
The patent replaces the simple source follow circuit with a transimpedance amplifier-based readout circuit. Although the amplifier circuit is more complex than the simple source follow circuit, it provides significantly improved sensitivity to thermal shocks and vibrations by reducing the electric time constant. The circuit complexity is justified by the substantial improvement in measurement precision and thermal stability.
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
The solution provides high thermal stability and enables seamless integration with existing signal processing circuits without the need for readout device modifications, reducing downtime and improving sensitivity to thermal shocks and vibrations.
Implementation Method 1
the electrical signal results from a charge transfer from the one electrode layer to the other electrode layer via the pyroelectric layer
Implementation Method 2
A signal amplifier circuit is included for the purpose of reading, amplifying, processing and/or relaying an electrical signal generated by the sensor chip
Data Source
AI summary
An infrared light detector including at least one sensor chip that has a layer element that is produced from a pyroelectrically sensitive material and further has a base electrode and a head electrode, to which the layer element is connected for tapping electric signals generated in the layer element by irradiation of the at least one sensor chip with light. The detector further includes a transimpedance amplifier for amplifying the signals with an operational amplifier, which is asymmetrically operated by a supply voltage source having a positive supply voltage and to the inverting input of which the base electrode is connected. At the voltage supply source, a voltage divider connected to ground is provided with a partial node, to which a partial voltage that is smaller than the supply voltage is applied and which is electrically coupled to the non-inverting input and to the head electrode.