Microcontroller Impedance Analyzer Using Square Wave Stimuli
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Solution Overview
Problem
Conventional microcontroller-based impedance analyzers require costly circuitry for digital frequency synthesis and high-resolution DACs to measure impedance at high precision and fine resolution, limiting their application due to the complexity and cost of the necessary circuitry.
Innovation Solution
The proposed solution utilizes general-purpose input/output functions of a microcontroller to generate a square wave stimulus and employs a clock circuitry to set both the stimulus and sampling frequencies, allowing for impedance measurement at high frequencies with reduced complexity and cost by using simple frequency divider functions and an anti-aliasing filter to minimize harmonic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microcontroller-based impedance analyzers use digital frequency synthesis and high-resolution DACs to measure impedance at high precision, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the complex digital frequency synthesis and high-resolution DAC functions from the microcontroller system, replacing them with a simpler square wave stimulus generator. This removes the need for costly digital frequency synthesis circuitry while maintaining measurement capability through alternative means (direct measurement of square wave response).
Solution Approach 2:
The patent replaces expensive, complex circuitry with simpler, cheaper components. The square wave stimulus approach uses basic digital output capabilities already present in most microcontrollers, eliminating the need for high-resolution DACs and complex frequency synthesis hardware, thereby reducing overall system cost and complexity.
2Measurement precision
If conventional impedance analyzers use sinusoidal stimulus with digital frequency synthesis, then measurement accuracy is maintained, but hardware cost increases
Solution Approach 1:
The patent changes the stimulus waveform parameter from sinusoidal to square wave. This parameter change allows the use of simpler digital output circuits while maintaining measurement accuracy through appropriate signal processing of the square wave response, thereby reducing manufacturing costs.
Solution Approach 2:
The patent substitutes complex electronic frequency synthesis mechanisms with a simpler digital switching approach. Instead of using DACs and analog filter networks to generate sinusoidal waves, the system uses direct digital square wave generation followed by digital signal processing, replacing complex analog/mixed-signal circuitry with simpler digital logic.
3Device complexity
If square wave stimulus is used to reduce hardware complexity, then device complexity is reduced, but harmonic interference increases
Solution Approach 1:
The patent converts the harmful harmonic content of the square wave stimulus into a beneficial feature by using it as a basis for frequency sweep measurements. The harmonics provide inherent frequency components that can be utilized to measure impedance across multiple frequencies simultaneously, turning a potential disadvantage into a measurement advantage.
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between the square wave stimulus and the impedance calculation. This intermediary layer filters and processes the response signal to extract accurate impedance information while rejecting harmonic interference, allowing the use of simple square wave generation without sacrificing measurement accuracy.
Data Source
AI summary
A microcontroller-based system for measuring the impedance of a device under test (DUT) (35) responsive to a square wave stimulus. A clock generator circuit (26) in the microcontroller (20) generates a clock signal at a base clock frequency. A first timer (25) divides down the base clock frequency by a first frequency divisor integer to set the stimulus frequency of a square wave generated by a general purpose input/output (GPIO) function (24), and a second timer (28) divides down the base clock frequency by a second frequency divisor integer to set the sampling frequency of an analog-to-digital converter (ADC) (30). A discrete Fourier transform executed by a processor (22) is used to determine the impedance of the DUT at the stimulus frequency. The first and second integers are selected so that aliased harmonics fall in different DFT bins from the fundamental tone.