Auto-Zeroing Sensor Readout for Parasitic Capacitance Drift
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Solution Overview
Problem
Electronic circuits implementing sensors, such as capacitive pressure sensors, face performance degradation due to time-varying parasitic capacitances caused by environmental factors like water droplets, which existing technologies have not effectively mitigated.
Innovation Solution
A sensor system comprising a sense capacitor with variable sense capacitance and a readout integrated circuit using a MASH modulator and auto-zeroing technique to generate ADC output signals, effectively mitigating the impact of time-varying parasitic capacitances by sampling and transferring charges during charging and integration phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional sensor circuits are used, then the circuit structure is simple, but the measurement precision deteriorates due to time-varying parasitic capacitances
Solution Approach 1:
The measurement process is segmented into distinct phases (sampling phase, hold phase, measurement phase) with dedicated circuit configurations for each phase. The readout circuit is divided into separate functional blocks including sampling capacitor, hold capacitor, and measurement amplifier, each optimized for its specific function to reject parasitic effects while maintaining overall system simplicity.
Solution Approach 2:
An intermediary hold capacitor is introduced between the sampling stage and the measurement stage. This hold capacitor acts as a buffer that isolates the measurement circuit from time-varying parasitic capacitances, allowing accurate measurement of the sampled voltage without direct exposure to parasitic effects during the measurement phase.
2Reliability
If environmental protection measures are added to mitigate water droplet effects, then the reliability improves, but the device complexity increases
Solution Approach 1:
The circuit converts the harmful effect of parasitic capacitances into a beneficial auto-zeroing mechanism. By intentionally sampling the parasitic capacitance effect during the sampling phase and storing it in the hold capacitor, the circuit automatically compensates for these effects during measurement, turning the harmful parasitic into a self-correcting feature without additional protection structures.
Solution Approach 2:
The circuit dynamically changes its electrical parameters (capacitance connections, voltage levels) through controlled switching between different phases. The readout circuit transitions between sampling mode and measurement mode by changing switch states and capacitor connections, allowing the same circuit to perform different functions at different times without structural modifications.
3Measurement precision
If sampling rate is increased to capture time-varying signals, then the measurement precision improves, but the use of energy increases
Solution Approach 1:
The circuit employs periodic phase switching between sampling and measurement modes at optimized frequencies. Rather than continuously operating at high sampling rates, the circuit uses periodic phase transitions to capture time-varying information during brief sampling intervals, then holds the value for measurement, reducing overall power consumption while maintaining accuracy for time-varying signals.
Solution Approach 2:
The sampling phase performs preliminary action by capturing the voltage value before parasitic effects can corrupt the measurement. By pre-sampling and holding the voltage in the hold capacitor during a controlled time window, the circuit ensures accurate capture of time-varying signals without requiring continuous high-speed sampling, thereby reducing energy consumption.
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
The solution significantly reduces the negative impact of time-varying parasitic capacitances, maintaining accurate pressure measurements by minimizing errors caused by water droplets and other low-frequency impairments, ensuring robust performance of the sensor system.
Implementation Method 1
a sensor comprising a sense capacitor with a variable sense capacitance; and a readout integrated circuit comprising an analog to digital converter (ADC)
Implementation Method 2
a variable parasitic capacitance is able to be coupled to the ADC input; and when an input pressure is sensed by the sensor, the variable sense capacitance is modulated, thereby generating one or more ADC output signals
Data Source
AI summary
Methods and devices to mitigate time varying impairments in sensors are described. The application of such methods and devices to pressure sensors facing time varying parasitic capacitances due to water droplets is detailed. Benefits of auto-zeroing technique as adopted in disclosed devices is also described.