PIR Sensor Readout Circuit With Dynamic Impedance Switching
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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 inefficient signal measurement due to self-charging, which complicates the design of measurement circuits and requires wide dynamic range and high impedance, making it challenging to implement effective and efficient measurement systems.
Innovation Solution
A high-impedance measuring circuit with a ΔΣ-converter and discharging circuit is developed, 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 and non-measurement phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the measurement circuit uses high input resistance to match the PIR detector's high internal resistance, then measurement precision is improved, but the circuit becomes overdriven due to accumulated charges
Solution Approach 1:
The patent applies dynamic impedance switching by using a switchable discharge path that alternates between high-impedance measurement mode and low-impedance discharge mode. The measurement circuit dynamically adjusts its input resistance based on operational phase, allowing high resistance during measurement for precision while enabling low resistance during discharge to prevent overdriving, thus resolving the contradiction between measurement accuracy and circuit stability
Solution Approach 2:
The patent implements periodic discharge cycles where the measurement circuit alternates between measurement phases and discharge phases. During measurement, the high input resistance maintains signal accuracy; during discharge phases, the circuit periodically lowers resistance to release accumulated charges. This periodic switching prevents permanent overdriving while maintaining measurement precision during active measurement windows
2Measurement precision
If the measurement circuit uses wide dynamic range to accommodate PIR detector output, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent uses partial action by implementing discrete impedance levels rather than continuous wide dynamic range. The discharge circuit provides targeted charge release at specific impedance levels, avoiding the need for continuously variable high-precision components that would consume more power. This partial approach achieves sufficient measurement accuracy without the power penalty of full wide dynamic range implementation
Solution Approach 2:
The patent changes the input resistance parameter dynamically between two distinct states: high resistance during measurement and low resistance during discharge. This binary parameter switching avoids the power consumption associated with maintaining wide dynamic range capabilities continuously, while still achieving the necessary measurement precision during active measurement phases through controlled parameter transitions
3Reliability
If discharge resistance is lowered to prevent overdriven conditions, then reliability is improved, but measurement precision deteriorates due to signal attenuation
Solution Approach 1:
The patent applies dynamic resistance switching where the discharge resistance is temporarily lowered only during discharge phases to prevent overdriving, then restored to high resistance during measurement phases to maintain signal precision. This temporal separation of resistance values allows the circuit to achieve both reliability during discharge and measurement precision during measurement without permanent compromise of either parameter
Solution Approach 2:
The patent implements periodic switching between high-resistance measurement mode and low-resistance discharge mode. During brief discharge intervals, low resistance prevents charge accumulation and overdriving; during extended measurement intervals, high resistance maintains signal fidelity. This periodic alternation ensures that signal attenuation during discharge does not permanently degrade measurement precision, as measurements occur during high-resistance phases
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 effectively prevents overdriven conditions, lowers power consumption, and enhances the accuracy of signal measurement by efficiently managing impedance and current distribution, thereby improving the reliability and efficiency of passive infrared radiation detection systems.
Implementation Method 1
passive infrared detectors (PIR) face issues with operating point drift and high internal resistance
Implementation Method 2
various known methods are used in the measurement of infrared radiation
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 integrating 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 integrator. A value of a current divider control signal driving the current divider control input depends at least indirectly from the digital integrator.