CTMU Impedance Measurement Using Differential Time Comparison
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Solution Overview
Problem
Existing impedance measurement methods using Charge Time Measurement Units (CTMU) face challenges in accurately determining impedance values due to variations in measurement conditions, making it difficult to precisely measure unknown impedances.
Innovation Solution
The apparatus and method employ a sensor circuit with a first portion having an unknown impedance and a second portion with a known impedance, using control logic to determine the measurement based on the difference in time each reaches a reference voltage, applying a current source or sink to a reference capacitor, and measuring the voltage after application and removal to calculate the impedance, allowing for precise measurement of variable capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If absolute measurements are used to determine unknown impedance with CTMU, then the measurement process is simple, but the measurement precision deteriorates due to variations in measurement conditions
Solution Approach 1:
The patent introduces a reference impedance circuit as an intermediary element to mediate the measurement process. By comparing the unknown impedance against a known reference impedance under identical measurement conditions, the system eliminates the impact of condition variations. The reference circuit serves as a stable benchmark that allows accurate determination of unknown impedance through differential measurement, resolving the contradiction between operational simplicity and measurement precision.
Solution Approach 2:
The patent transforms the measurement approach by changing from absolute impedance measurement to differential measurement based on time difference. Instead of directly measuring absolute impedance values which are sensitive to condition variations, the system measures the time difference for voltage to reach a reference level, which is then used to calculate impedance. This parameter transformation makes the measurement robust against condition variations while maintaining simplicity.
2Measurement precision
If a bridge sensor circuit with comparators and timing capacitor is used, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent segments the measurement function into distinct modular components: a bridge sensor circuit with separate arms for unknown and reference impedance, comparator units for voltage level detection, and a timing capacitor for time difference measurement. Each component performs a specific function, making the complex measurement task manageable and the circuit structure organized. This segmentation allows high precision measurement while keeping the design systematic and maintainable.
3Measurement precision
If time difference measurement method is used to determine impedance, then the measurement precision improves, but the measurement time increases
Solution Approach 1:
The patent employs periodic action through the use of a timing capacitor that is repeatedly charged and discharged in each measurement cycle. The capacitor charges during the measurement phase to capture the time difference, then discharges to reset the system for the next measurement. This periodic charge-discharge cycle enables continuous high-precision measurements without accumulating errors, balancing measurement precision with efficient time utilization.
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 enables high-precision measurement of unknown impedances by accurately determining the difference in capacitances, providing a cost-effective and accurate method for measuring reactive elements in sensor circuits, such as those used in environmental sensors, with high accuracy and low power consumption.
Implementation Method 1
apply a current source or sink to a reference capacitor; based on a determination that the first input has reached the reference voltage, remove the current source or sink from the reference capacitor; and determine the measurement of the sensor circuit based upon a voltage of the reference capacitor
Data Source
AI summary
A method and apparatus for measuring an unknown impedance. The apparatus comprises a first input to receive a first signal generated by a first portion of a sensor circuit, the first portion comprising an unknown impedance and a first known resistance, the unknown impedance to vary based upon a phenomenon to be measured by the sensor circuit. The apparatus also comprises a second input to receive a second signal generated by a second portion of the sensor circuit, the second portion of the sensor circuit comprising a known impedance and a second known resistance. And the apparatus comprises control logic to, based on a difference in time at which each of the first input and the second input reach a reference voltage, determine a measurement of the sensor circuit.