FMCW Distance Measurement with Oversampled Digital Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional FMCW radar-based fill-level measurement devices face high implementation costs and reduced accuracy due to the need for complex, high-order analog filters that are sensitive to component tolerances and temperature variations.
Innovation Solution
An FMCW radar-based distance measuring device that incorporates digital filtering and oversampling, reducing the complexity of analog components by using first-order filters and 12-bit converters, and employing digital high-pass and low-pass filters to maintain accuracy and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-order analog filters are used to achieve sufficient filter sharpness, then filtering performance is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent replaces complex analog filtering (mechanical/electrical system with multiple components) with digital filtering implemented in software. The analog-to-digital converter digitizes the signal, and subsequent digital signal processing performs the filtering function that would otherwise require high-order analog filters with numerous capacitors and inductors. This substitution dramatically reduces component count and device complexity while maintaining or improving filtering performance.
Solution Approach 2:
The patent changes the operating parameters of the analog-to-digital converter, specifically using oversampling with a sampling rate at least four times the frequency of the evaluation signal. This parameter change enables the use of simpler analog filters (first-order or second-order) before digitization, because the oversampled digital signal can be effectively filtered using digital processing techniques that are less sensitive to analog filter imperfections.
2Measurement precision
If high-order analog filters are used to achieve sufficient filter sharpness, then filtering performance is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive high-order analog filters (requiring precision capacitors and inductors) with digital filtering algorithms running on a microcontroller or processor. Digital filters can be implemented in software without additional hardware components, significantly reducing bill of materials costs. The analog-to-digital converter and simple first-order or second-order analog filters before conversion are much cheaper than the high-order analog filters they replace.
Solution Approach 2:
The patent uses inexpensive first-order or second-order analog filters followed by digital processing instead of expensive high-order analog filters. The simple analog filters have fewer precision components and are cheaper to manufacture, while the filtering functionality is completed by software-based digital filters that have negligible marginal cost.
3Measurement precision
If high-order analog filters are used to achieve sufficient filter sharpness, then filtering performance is improved, but temperature stability and robustness deteriorate
Solution Approach 1:
The patent replaces temperature-sensitive high-order analog filters with digital filters implemented in software. Digital filters are not affected by temperature variations, component tolerances, or aging effects that plague analog filters. The filtering algorithm remains stable and precise across the full operating temperature range, eliminating the robustness problems inherent in complex analog filter designs.
Solution Approach 2:
The patent changes the filtering approach from analog to digital domain, where filter characteristics are defined by software parameters rather than physical component values. This parameter change makes the filter immune to temperature-induced drift and component tolerance variations, significantly improving reliability and stability.
4Device complexity
If oversampling is used with simple analog filters, then device complexity is reduced, but signal-to-noise ratio may deteriorate
Solution Approach 1:
The patent uses digital filtering to restore and improve the signal-to-noise ratio after oversampling. The digital filter can selectively pass the evaluation signal frequency while rejecting noise components, achieving better signal-to-noise ratio than the simple analog filters alone. This digital post-processing compensates for any noise introduced by the simplified analog filtering and oversampling approach.
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
Reduces costs and complexity while maintaining high accuracy and reducing temperature dependence, with improved signal-to-noise ratio and sensitivity through digital filtering and oversampling.
Implementation Method 1
a signal-generating unit, which is designed to generate a radio-frequency electrical signal according to the FMCW principle, and to generate an evaluation signal by mixing the radio-frequency signal with a received signal
Implementation Method 2
generate an evaluation signal by mixing the radio-frequency signal with a received signal
Implementation Method 3
an antenna arrangement, by means of which the radio-frequency signal can be emitted as a radar signal in the direction of the object and can be received as a corresponding received signal after reflection on the object
Implementation Method 4
received as a corresponding received signal after reflection on the object
Implementation Method 5
a first analog signal-processing unit for processing the evaluation signal, having, each arranged in series, a first analog high-pass filter, a first amplifier, and a first analog low-pass filter
Implementation Method 6
a first analog/digital converter, which is designed to digitize the evaluation signal, processed by the analog signal-processing unit, by means of oversampling
Implementation Method 7
a first digital low-pass filter for filtering the evaluation signal, optionally a first decimator for decimation of the digitized evaluation signal, a first digital high-pass filter for filtering the optionally decimated evaluation signal
Implementation Method 8
a computing unit which is designed to determine the distance on the basis of the digitally filtered evaluation signal, especially by means of a Fourier transform
Data Source
AI summary
An FMCW-radar based distance measuring device is characterized in that, in addition to analogue high-pass and low-pass filtering, the evaluation signal typical for FMCW additionally undergoes subsequent digital filtering. In this case, the analogue/digital conversion takes place by oversampling. As a result, according to the invention, all those frequencies in the evaluation signal that are above or below the frequency corresponding to the distance of the object are effectively suppressed. At the same time, the analogue filters can be constructed with a very low level of complexity. The space requirement and the costs of the analogue components is reduced thereby. In addition, the dependence on temperature of the distance measuring device is reduced thereby. The potentially high distance resolution is also maintained.