Electronic Filter Cutoff Estimation Using Two Calibration Frequencies
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Solution Overview
Problem
Existing methods for estimating the cut-off frequencies of electronic filters in wireless RF transceivers, such as those used in Bluetooth Low Energy devices, face challenges due to process and temperature variations, requiring additional hardware and being either inaccurate or time-consuming, especially in battery-powered devices.
Innovation Solution
A method involving the generation of modulated signals by a local oscillator to estimate the cut-off frequency of electronic filters using two distinct calibration frequencies, eliminating the need for a replica filter and reducing measurement time, while allowing for internal signal generation and minimal extra components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a replica filter is used to estimate the cut-off frequency, then the cut-off frequency can be estimated, but additional hardware is required which increases IC/PCB area and power consumption
Solution Approach 1:
The patent uses a digital copy of the filter transfer function implemented in software rather than a physical replica filter. The processor executes instructions that mathematically model the filter's frequency response, eliminating the need for duplicate hardware components while maintaining estimation accuracy.
Solution Approach 2:
The patent replaces the mechanical/physical replica filter system with a computational/software-based system. Instead of using physical RC time constant measurement hardware, the solution uses digital signal processing and mathematical calculations to estimate the cut-off frequency, thereby reducing hardware complexity.
2Device complexity
If a frequency sweep is applied to measure the cut-off frequency directly, then no additional hardware is required, but the measurement process becomes very slow
Solution Approach 1:
The patent performs preliminary characterization of the filter's transfer function during manufacturing or initial setup, storing the nominal transfer function in memory. This pre-computed information is then used during operation to quickly estimate cut-off frequency without requiring time-consuming real-time frequency sweeps, thus reducing measurement time while maintaining accuracy.
Solution Approach 2:
The patent changes the approach from measuring across a full frequency range to evaluating the transfer function at specific critical parameters (such as the cut-off frequency point). By focusing measurements or calculations on key parameters rather than sweeping through all frequencies, the estimation process becomes much faster while still providing accurate results.
3Measurement precision
If process and temperature variations are compensated through calibration, then cut-off frequency accuracy is improved, but additional calibration hardware and time are required
Solution Approach 1:
The patent implements self-calibration capabilities where the transceiver uses its own internal resources (processor, existing signal generation capabilities, and stored nominal transfer function) to perform cut-off frequency estimation and compensation. No external calibration equipment or additional dedicated calibration hardware is required, as the system calibrates itself using available internal components.
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 approach provides accurate and efficient estimation of cut-off frequencies with reduced hardware requirements and power consumption, enabling smaller transceiver size and lower production costs, while allowing for in-field calibration without external input.
Implementation Method 1
generating a first and a second modulated synthesised signal by modulating a signal output by a local oscillator with respective first and second modulations
Implementation Method 2
mixing a radio-frequency continuous-wave signal with the first modulated synthesised signal in order to generate a first signal at a first frequency
Implementation Method 3
electronic filters, e.g. anti-aliasing filters, in a receive chain thereof in order to aid successful reception of signals by filtering out spurious high and/or low-frequency components
Data Source
AI summary
The cut-off frequency of an electronic filter having a nominal transfer function and a nominal cut-off frequency is estimated by: applying a first signal at a first frequency to an input of the filter while sampling an output of the filter in order to obtain a first magnitude measurement, the first frequency being less than the nominal cut-off frequency; applying a second signal at a second frequency to the input of the filter while sampling the output of the filter in order to obtain a second magnitude measurement, the second frequency being greater than the nominal cut-off frequency; and estimating the cut-off frequency of the filter based on the nominal transfer function, the first magnitude measurement, and the second magnitude measurement.