PIR Sensor Charge Discharge Control for Stable Dynamic Range
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Passive infrared detectors (PIR) face challenges with self-charging issues that shift the operating point and require high internal resistance in evaluation circuits, leading to overdriving and limited dynamic range, which complicates signal evaluation and power consumption.
Innovation Solution
A device with a discharge network connected to the PIR detector and an analog-to-digital converter, utilizing leakage resistors and switched capacitor circuits to manage charge discharge, and a current divider with a resistor chain for digital control of current feedback, allowing for high-resistance measurement without overloading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high internal resistance is used in the evaluation circuit to handle the PIR detector's low current, then the current measurement capability is improved, but the circuit cannot discharge accumulated charges leading to overdriving and limited dynamic range
Solution Approach 1:
The patent applies the dynamics principle by making the discharge resistance variable rather than fixed. The discharge resistance is adjusted dynamically based on the operating conditions: it is increased when the PIR detector generates large charges (to prevent overdriving) and decreased when charges need to be discharged (to maintain dynamic range). This dynamic adjustment resolves the contradiction between maintaining high input resistance for accurate current measurement and providing charge discharge capability for extended dynamic range.
2Reliability
If leakage resistors are used to discharge the PIR detector connections, then charge discharge is achieved, but the signal and detector noise are continuously attenuated
Solution Approach 1:
The patent implements dynamic control of the discharge resistance to eliminate continuous signal attenuation. The discharge path is activated only when needed (when charge accumulation threatens to overdrive the circuit), and the resistance value is adjusted based on the detector's charge state. This selective, dynamic discharge mechanism maintains high signal fidelity while providing necessary charge management, resolving the contradiction between reliability and measurement precision.
3Measurement precision
If the PIR detector operates with self-charging, then the operating point shifts, but using a high-resistance evaluation circuit prevents charge discharge causing overdriving
Solution Approach 1:
The patent employs feedback control to monitor the charge state of the PIR detector and adjust the discharge resistance accordingly. The evaluation circuit continuously assesses the detector's operating conditions and dynamically modifies the discharge path resistance to maintain the operating point within the optimal range. This feedback mechanism prevents both operating point drift and overdriving, resolving the contradiction between measurement precision and adaptability.
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 solution enables efficient suppression of quantization errors, maintains a stable operating point, and minimizes power consumption while providing a large dynamic range for PIR signal evaluation.
Implementation Method 1
passive infrared detectors (PIR detectors)... measuring infrared radiation... the current source I PIR supplies a current I PIR depending on the change in irradiation and thus the temperature
Implementation Method 2
discharge network R G... leakage resistors... The resistance value of these leakage resistors should be greater than 1 MOhm, preferably greater than 10 MOhm, preferably greater than 100 MOhm, and preferably greater than 1 GOhm
Implementation Method 3
switched capacitor circuits to manage charge discharge
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a device for operating a passive infrared detector (PIR). The passive infrared detector (PIR) is discharged by means of a discharging network (RG) during charging and preferably not during the measurement. The discharging network (RG) and the infrared detector (PIR) are connected to an analog-to-digital converter (ADC), which converts the signal of the infrared detector into a digital signal on the output bus T at least at times. The output (T) of the analog-to-digital converter (ADC) is connected to a subsequent digital filter (DF). The bus bandwidth of the output (Out) of the digital filter (DF) is typically greater than the bus bandwidth of the output (T) of the analog-to-digital converter (ADC).