Pyroelectric Motion Detector ADC Windowing for RF-Noise Immunity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low-cost home security motion detectors face challenges in improving performance due to cost constraints, with small desired signals being buried in noise and sensitive to RF radiation, requiring expensive active circuitry and large capacitors.
Innovation Solution
A novel microcontroller with a compact 8-bit processor, high-resolution differential input sigma-delta ADC, and programmable gain differential output amplifier, using internal reference voltages to center and size the ADC input window, eliminating the need for external capacitors and amplifiers, and providing direct connection to pyroelectric sensors for improved RF insensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC coupling with large capacitance and discrete operational amplifiers is used to block DC offset and amplify the desired signal, then the desired signal can be extracted from noise, but the cost and device complexity increase significantly
Solution Approach 1:
The patent combines the DC blocking capacitor and signal amplification functions into a single integrated operational amplifier within the microcontroller. The op-amp is configured with capacitive coupling internally, eliminating the need for external large capacitance components and discrete amplifiers, thus reducing device complexity while maintaining signal detection precision.
Solution Approach 2:
The microcontroller's integrated operational amplifier serves multiple functions: it blocks the DC offset voltage, amplifies the small desired signal, and provides impedance matching for the pyroelectric sensor. This multi-functionality reduces the number of external components needed, lowering overall system cost and complexity while maintaining measurement precision.
2Measurement precision
If discrete operational amplifiers and large capacitance components are used to process the desired signal, then noise filtering and signal amplification are achieved, but the cost of the motion detector increases
Solution Approach 1:
The patent replaces expensive discrete operational amplifiers and large capacitance components with a low-cost integrated operational amplifier built into the microcontroller. This integration dramatically reduces the bill of materials cost while maintaining the signal-to-noise ratio through the op-amp's inherent amplification and filtering capabilities.
Solution Approach 2:
The microcontroller's integrated operational amplifier automatically performs DC blocking and signal amplification without requiring external passive components. The internal capacitive coupling and amplification circuitry handle signal conditioning autonomously, eliminating the need for additional expensive external components and simplifying the manufacturing process.
3Measurement precision
If external capacitors and active circuitry are added to improve signal processing, then desired signal extraction is improved, but the device becomes more sensitive to RF radiation and other interferences
Solution Approach 1:
The patent removes external capacitors and discrete active circuitry from the signal path, keeping only the essential pyroelectric sensor and lens. By eliminating external passive components that can act as antennas or coupling elements for RF interference, the system becomes less sensitive to RF radiation while maintaining desired signal extraction through the integrated operational amplifier inside the microcontroller.
4Measurement precision
If high-resolution ADC and sophisticated signal processing are implemented, then measurement precision improves, but processing load on the microcontroller increases
Solution Approach 1:
The operational amplifier performs preliminary signal conditioning and amplification before the ADC conversion, pre-processing the signal to the optimal level. This preliminary action ensures that the ADC receives a well-conditioned signal that maximizes conversion efficiency and minimizes the computational burden on the microcontroller for subsequent processing, thus maintaining high measurement precision without excessive processing load.
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 enhances RF radiation insensitivity and maintains low-cost functionality, increasing effective ADC resolution and reducing processing load, making the motion detector suitable for cost-sensitive applications while meeting future EMC testing requirements.
Implementation Method 1
The motion detector 1 detects motion by detecting infrared radiation emitted by a person. For example, the face of a person emits a substantial amount of infrared radiation that usually can be detected at a reasonable distance under normal lighting and temperature conditions by a passive infrared (PIR) sensor 2. PIR sensor 2 is also referred to as a pyroelectric sensor.
Data Source
AI summary
A microcontroller has a compact 8-bit processor and a differential input sigma-delta ADC (SDADC). In a low-cost pyroelectric sensor motion detector application, a sensor output signal is supplied onto a second differential input of the SDADC. A first programmable internal reference voltage source supplies VREF1 via an internal signal path onto a first differential input of the SDADC. A second programmable internal reference voltage source supplies VREF2 onto a reference voltage input of the SDADC. VREF1 sets the center of the SDADC input sample window, thereby avoiding the need to provide an external AC blocking capacitor. VREF2 sets the size of the window. Proper window sizing and sample averaging and the high-resolution SDADC obviate the need for input signal amplification. Throughput requirements on the 8-bit processor are reduced by providing a hardware averager and associated DMA controller, thereby making the overall solution a low-cost, noise-insensitive, solution.