Sensor Measurement Circuit Reducing Terminal Count
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Solution Overview
Problem
Existing measurement circuits for sensors, particularly in MEMS and NEMS, face challenges due to parasitic resistances and complexity, especially when using Wheatstone bridges, which require multiple terminals and complex current-to-voltage conversion, increasing cost and complexity.
Innovation Solution
A measurement circuit with a detection branch comprising two series of dipoles connected in parallel, using a bias circuit to apply a bias current and a read circuit with a voltage-controlled current source to maintain a reference potential, allowing for impedance variation determination without additional reference resistors and minimizing terminal count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Wheatstone bridge is used for sensor measurement, then measurement precision is improved, but device complexity increases due to multiple terminals and current-to-voltage conversion requirements
Solution Approach 1:
The patent extracts the measurement function from the traditional Wheatstone bridge configuration by using a single impedance element connected to a summing node. The measurement is performed by applying a test signal and measuring the resulting voltage at the summing node, eliminating the need for bridge balance and multiple reference elements. This reduces circuit complexity while maintaining measurement precision.
Solution Approach 2:
The summing node serves multiple functions: it acts as the measurement point for impedance detection, the input node for the test signal, and the reference potential point. This multi-functionality eliminates the need for separate current-to-voltage conversion circuits and reduces the number of terminals required, thereby reducing device complexity.
2Measurement precision
If four-point connection technique is used to overcome parasitic resistances, then measurement precision is improved, but quantity of substance increases due to doubled terminals
Solution Approach 1:
The patent merges the test signal application and measurement functions into a single terminal connection. The impedance element is connected between a signal node and a summing node, both of which are accessible through the same terminal. This merging eliminates the need for separate four-point connection terminals while maintaining precision by using a virtual ground reference at the summing node that is insensitive to parasitic resistances.
Solution Approach 2:
The summing node acts as an intermediary that provides a virtual ground reference potential. By maintaining this node at a stable reference potential through the operational amplifier, the circuit eliminates the impact of parasitic resistances on the measurement without requiring additional physical terminals for four-point connection.
3Ease of operation
If current source is used to bias the impedance, then ease of operation is improved, but device complexity increases due to need for current-to-voltage conversion
Solution Approach 1:
The summing node serves as both the current summing point and the voltage output point. The operational amplifier maintains this node at a virtual ground potential, directly converting the input current from the impedance element into an output voltage without requiring a separate current-to-voltage conversion stage. This multi-functionality simplifies the circuit while maintaining ease of operation.
Solution Approach 2:
The operational amplifier's virtual ground mechanism automatically performs the current-to-voltage conversion function. The amplifier adjusts its output to maintain the summing node at reference potential, thereby self-converting the input current signal into a proportional output voltage signal without requiring external conversion circuitry.
Data Source
AI summary
A measurement circuit for a sensor, the measurement circuit includes at least one detection branch including at least a first series of at least one dipole and a second series of at least one dipole, the series being connected in parallel and connected at their inputs to a common input terminal, each series of dipole being connected to a distinct output terminal, and an electronic circuit including a bias circuit configured to apply a bias current to the detection branch from the input terminal, and a read circuit configured to impose on each output terminal the same potential referred to as the “reference potential” (VREF); the electronic circuit including a determination circuit for determining variations in impedances of each series of dipole of the detection branch on the basis of the current applied to each output terminal by the read circuit so as to keep the potentials equal.