Impedance Sensing via Dual Digital Conversion
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Solution Overview
Problem
Conventional impedance sensing techniques are complex, expensive, and limited to capacitive sensing, failing to effectively separate resistance and capacitance contributions in serial or parallel RC circuits, and are not suitable for low-cost, low-power applications in fields like automotive, IoT, and consumer devices.
Innovation Solution
The development of low-cost impedance sensing methods using a two-frequency method or double-sampling single-frequency method, which involve ratio-metric measurements and differential modulator front-end circuits to convert impedance attributes into digital values, allowing for robust and efficient sensing of both serial and parallel RC sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional impedance sensing techniques are used, then measurement capability is provided, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex conventional impedance sensing circuits with a simplified capacitive sensing architecture that uses a single capacitor and switched capacitor network. The impedance sensing function is achieved through capacitive division and digital conversion rather than traditional analog impedance measurement circuits, significantly reducing component count and complexity while maintaining measurement capability.
Solution Approach 2:
The sensing circuit is designed to measure both serial and parallel RC sensor configurations using the same basic architecture. The circuit can sense both capacitance and resistance by adjusting the switching sequence and measurement mode, providing universal impedance sensing capability without requiring separate dedicated circuits for different sensor types.
2Measurement precision
If conventional impedance sensing techniques are used, then measurement capability is provided, but manufacturing cost increases
Solution Approach 1:
The patent uses inexpensive switched capacitor components and standard digital logic elements that can be easily integrated into ASICs or FPGA devices. The sensing circuit relies on off-the-shelf capacitors and digital converters rather than expensive specialized impedance measurement instruments, dramatically reducing per-unit manufacturing cost while maintaining adequate measurement precision for practical applications.
3Measurement precision
If conventional impedance sensing techniques are used, then capacitive sensing is provided, but ability to separate resistance and capacitance contributions is limited
Solution Approach 1:
The patent segments the impedance measurement into separate capacitive and resistive components through distinct measurement phases. The capacitive component is measured during phases when the switching network connects specific capacitors to the sensor, while the resistive component is measured during different phases using the same physical components. This temporal and functional segmentation allows independent extraction of R and C contributions from the overall impedance.
Solution Approach 2:
The sensing circuit employs periodic switching sequences that alternate between different measurement configurations. By periodically switching the capacitor network in specific patterns and sampling at different phases of the switching cycle, the circuit can distinguish between resistive and capacitive effects through their different temporal responses, enabling separate measurement of both components using the same hardware.
4Measurement precision
If conventional impedance sensing techniques are used, then sensing capability is provided, but power consumption increases
Solution Approach 1:
The patent implements periodic switching and sampling rather than continuous measurement. The capacitor network is switched and sampled at discrete intervals, allowing the system to enter low-power states between measurements. This periodic operation mode significantly reduces average power consumption compared to continuous analog impedance sensing while maintaining measurement accuracy through adequate sampling rates.
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
These methods provide reliable and efficient impedance sensing capabilities, independent of clock frequencies and supply variations, enabling accurate measurement of sensor capacitance and resistance without depending on excitation frequency, thus addressing the limitations of conventional techniques.
Implementation Method 1
Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance
Implementation Method 2
The electrical circuit converts one or more attributes, such as the measured capacitances of the capacitive sense elements or the measured resistance of the sense elements, into digital values
Data Source
AI summary
Apparatus and methods of impedance sensing are described. One method includes performing a first digital conversion of an attribute of a sensor electrode and performing a second digital conversion of the attribute of the sensor electrode. The second digital conversion differs by at least one characteristic from the first digital conversion. The method further includes calculating a resistance of the sensor electrode from a first and second digital value of the first and second digital conversions, respectively; and calculating a capacitance of the sensor electrode from the first and second digital value of the first and second digital conversions, respectively.