Ultrasonic Receiving Circuit Synchronous Rectifier Detection
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Solution Overview
Problem
Existing ultrasonic occupancy and vacancy sensors face challenges in distinguishing small-magnitude Doppler-shifted ultrasonic waves from non-Doppler-shifted waves, limiting their ability to detect occupancy or vacancy conditions effectively, particularly due to sensitivity to thresholds and limitations in signal-to-interference ratio (SIR) and ADC quantization noise.
Innovation Solution
An ultrasonic receiving circuit comprising an ultrasonic receiving element, an amplifier circuit, a synchronous rectifier, and a filter, which generates a filtered signal indicating occupancy by exceeding a threshold magnitude, allowing for improved detection of small-magnitude ultrasonic waves with a synchronous rectifier that works across a wider range of signal-to-interference ratios, including those as low as −80 dB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard ultrasonic receiving circuits with fixed threshold comparators are used, then the circuit operation is simple, but the detection precision deteriorates for small-magnitude Doppler-shifted signals with SIR less than -40 dB
Solution Approach 1:
The patent changes the operating parameters of the receiving circuit by implementing variable gain amplification stages and adjustable threshold levels. The first amplifier circuit provides initial amplification with a first gain, and a second amplifier circuit provides additional amplification with a second gain that can be adjusted based on signal strength. This allows the circuit to adapt to very weak Doppler-shifted signals while maintaining simple overall architecture.
Solution Approach 2:
The patent introduces dynamic threshold adjustment mechanisms where the threshold level is not fixed but can change based on the received signal characteristics. The control circuit dynamically adjusts the threshold comparison level to optimize detection of small-magnitude signals while preventing false detections from noise, enabling precise detection across varying signal conditions without complex circuitry.
2Measurement precision
If ADC quantization is used for signal processing, then digital processing is achieved, but quantization noise limits the detection of small-magnitude ultrasonic waves
Solution Approach 1:
The patent applies preliminary amplification to the ultrasonic signal before it undergoes ADC quantization. By amplifying the weak Doppler-shifted signal in the analog domain using the first and second amplifier circuits, the signal magnitude is increased to a level where subsequent digital processing does not introduce significant quantization noise relative to the signal strength, thereby improving detection accuracy.
Solution Approach 2:
The patent introduces an intermediate analog amplification stage between the ultrasonic receiving element and the ADC converter. This intermediary amplifier circuit acts as a mediator that boosts the weak ultrasonic signal to an appropriate level for digital conversion, reducing the impact of quantization noise while maintaining signal integrity throughout the processing chain.
3Reliability
If fixed threshold comparators are used, then the circuit is simple to implement, but the signal-to-interference ratio performance deteriorates for SIR less than -40 dB
Solution Approach 1:
The patent implements dynamic threshold adjustment where the comparator threshold is not fixed but adapts based on the amplified signal characteristics. The control circuit monitors the received signal strength and dynamically adjusts the threshold level to maintain optimal detection performance across varying SIR conditions, including very low SIR scenarios below -40 dB, thereby improving occupancy detection reliability.
Solution Approach 2:
The patent changes the operational parameters of the comparison stage by introducing variable threshold levels and adjustable gain settings. The amplifier circuits provide variable gain control, and the comparator uses adjustable thresholds, allowing the system to optimize its detection parameters for different signal conditions and maintain high reliability even with simple overall circuit architecture.
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 enables effective detection of occupancy or vacancy conditions with improved sensitivity and accuracy, overcoming the limitations of prior art by using a synchronous rectifier that can handle very small input signals and reduce noise, enhancing the signal-to-interference ratio and enabling reliable operation across a broader range of signal conditions.
Implementation Method 1
an ultrasonic receiving element for generating an ultrasonic input signal
Implementation Method 2
a synchronous rectifier for rectifying the input signal to generate a rectified signal
Implementation Method 3
a filter for filtering the rectified signal to generate a filtered signal
Data Source
AI summary
An ultrasonic occupancy sensor for detecting presence or absence of an occupant in a space includes an ultrasonic receiving circuit having a synchronous rectifier that allows the circuit to detect small-magnitude ultrasonic waves having a Doppler shift. The sensor comprises an ultrasonic transmitter for transmitting ultrasonic waves at an ultrasonic operating frequency, and a controller that drives the transmitting circuit with complementary drive signals to control the ultrasonic operating frequency. The synchronous rectifier receives the drive signals from the controller and rectifies an amplified input signal to generate a rectified signal, which is filtered by a filter to generate a filtered signal. The controller receives the filtered signal and determines that the space is occupied if the magnitude of the filtered signal exceeds a threshold. The ultrasonic occupancy sensor may also include a low phase-noise oscillator circuit coupled to the controller for setting an internal operating frequency of the controller.