PIR Sensor Readout Circuit With Dynamic Discharge Control
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Solution Overview
Problem
Passive infrared detectors (PIR) face issues with operating point drift and high internal resistance, leading to overdriven conditions and inefficiencies in measurement circuits, particularly due to self-charging and low current delivery, which require wide dynamic range amplifiers and high resistance values, making signal measurement challenging and power consumption high.
Innovation Solution
A high-impedance measuring circuit with a ΔΣ-converter and discharging circuit is implemented, where the discharging resistors are adjusted based on the PIR detector's requirements, and a current divider is used in the differential amplifier to manage current distribution, allowing for efficient suppression of quantization errors and preventing overdriven conditions by dynamically switching impedance states during measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the PIR detector operates with high internal resistance to maintain wide dynamic range, then measurement precision is improved, but the circuit becomes overdriven and unstable due to charge accumulation
Solution Approach 1:
The patent applies dynamics by making the discharge resistance variable rather than fixed. The discharge resistance is dynamically adjusted based on the operating conditions of the PIR detector, allowing the circuit to maintain stability while preserving measurement precision. The control unit monitors the detector state and adjusts the discharge resistance accordingly, transforming a static circuit into a dynamic adaptive system.
Solution Approach 2:
The patent changes the parameter of discharge resistance from a fixed value to a variable parameter that can be adjusted based on operating conditions. By modifying the discharge resistance parameter dynamically, the system resolves the contradiction between maintaining high input resistance for precision and preventing charge accumulation for stability.
2Reliability
If the discharge resistance is lowered to prevent overdriven conditions, then circuit stability is improved, but measurement precision deteriorates due to signal attenuation
Solution Approach 1:
The system dynamically adjusts the discharge resistance based on real-time operating conditions. During normal measurement operations, the discharge resistance is kept high to maintain precision. When charge accumulation threatens to overdrive the circuit, the resistance is lowered to restore stability, then raised again for continued measurement.
Solution Approach 2:
The discharge resistance is periodically adjusted in response to the charging-discharging cycle of the PIR detector. The control unit monitors the detector state and periodically modifies the discharge resistance to maintain the circuit within optimal operating parameters, preventing overdriven conditions while preserving signal integrity.
3Measurement precision
If a fixed high discharge resistance is used to maintain wide dynamic range, then measurement capability is improved, but power consumption increases due to continuous charge accumulation
Solution Approach 1:
The patent changes the discharge resistance from a fixed high value to a dynamically adjustable parameter. By lowering the resistance only when necessary to discharge accumulated charge, the system maintains wide dynamic range during measurement while reducing power consumption during discharge phases, optimizing the energy-performance tradeoff.
Solution Approach 2:
The system employs periodic discharge cycles rather than continuous discharge. The discharge resistance is activated periodically to remove accumulated charge when needed, then deactivated to preserve signal integrity during measurement, thereby reducing overall power consumption while maintaining measurement capability.
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 effectively prevents overdriven conditions, lowers power consumption, and enhances the dynamic range of the measurement circuit, allowing for accurate signal evaluation and efficient operation of PIR detectors by dynamically managing impedance and current distribution.
Implementation Method 1
passive infrared detectors (PIR) face issues with operating point drift and high internal resistance
Implementation Method 2
the measurement of infrared radiation
Implementation Method 3
a discharging circuit RG is connected to the PIR detector
Data Source
AI summary
A system for measuring a sensor having two terminals includes first and second transistors with first and second control signal inputs connected to the sensor terminals. The system further includes a current divider including a reference current input, a current divider control input and first and second current outputs connected to the first and second transistors. First and second load circuits are connected to the first and second transistors at first and second differential output nodes. First and second integrator circuits are connected to the first and second differential output nodes. A comparator is driven by first and second differential output nodes. The comparator output controls a digital filter. A value of the a current divider control signal driving the current divider control input depends at least indirectly from the digital filter output.