Multi-Sensor Impedance Circuit With Switch Isolation
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Solution Overview
Problem
In impedance measuring semiconductor circuits, sensors are affected by currents applied to other sensors, leading to measurement errors due to indirect and direct influences, as well as noise interference, resulting in inaccurate impedance measurements.
Innovation Solution
The implementation of an impedance measuring semiconductor circuit with analog switches in a negative feedback loop, including a first and second output-side switch and input-side switch, which isolate sensors during measurement, allowing for accurate impedance determination by decoupling sensors and reducing the influence of on-resistances and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensors are coupled to a measuring object and currents are measured by switching of analog switches, then measurement capability is improved, but sensors affect each other causing measurement errors
Solution Approach 1:
The patent divides the measurement circuit into separate measurement periods for each sensor. The analog switches are configured to connect only one sensor to the operational amplifier at a time, segmenting the measurement process temporally. This prevents direct current interference between sensors while maintaining the ability to measure multiple sensors sequentially.
Solution Approach 2:
The patent applies preliminary action by pre-charging or pre-discharging the operational amplifier's input capacitance during switching transitions. Before connecting a new sensor, the circuit performs preparatory switching operations to eliminate residual charges that could cause measurement errors, ensuring clean measurement conditions are established in advance.
2Adaptability or versatility
If analog switches are used to switch between sensors, then multi-sensor measurement capability is improved, but on-resistance and noise affect measurement accuracy
Solution Approach 1:
The patent introduces an intermediary capacitor connected to the operational amplifier's input terminal. This capacitor acts as a mediator that isolates the high-impedance sensor from the switching network's resistance and noise. By charging/discharging this intermediary capacitor during switching, the circuit transfers charge without allowing direct current paths through the analog switch resistances, thereby maintaining measurement accuracy while enabling multi-sensor capability.
3Productivity
If sensors are measured simultaneously, then measurement efficiency is improved, but cross-talk between sensors causes errors
Solution Approach 1:
The patent implements periodic action by rapidly alternating between sensors in a time-division multiplexing scheme. Each sensor is connected to the operational amplifier for a brief periodic interval, and the measurement is completed within this short window. The switching frequency is high enough that the sensors appear to be measured simultaneously for practical purposes, yet the sequential connection prevents cross-talk, maintaining both efficiency and accuracy.
Data Source
AI summary
A provided impedance measuring semiconductor circuit can suppress the influence of sensors on the measurements of other sensors in the measurements of the sensors. According to an embodiment, an impedance measuring semiconductor circuit includes a first resistance element, an operational amplifier having a positive input terminal and an output terminal, the positive input terminal receiving a predetermined set voltage, the output terminal being coupled to one end of the first resistance element, a first output-side switch that electrically couples or decouples a first sensor and the other end of the first resistance element, a second output-side switch that electrically couples or decouples a second sensor and the other end of the first resistance element, a first input-side switch that electrically couples or decouples the first sensor and a negative input terminal, and a second input-side switch that electrically couples or decouples the second sensor and the negative input terminal.