Switched Capacitor Circuit for Humidity Sensing
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Solution Overview
Problem
Existing humidity detecting devices face challenges in accurately measuring humidity due to issues with parasitic capacitance, leakage currents, and power consumption, particularly in the design of capacitance-type humidity sensors that rely on moisture-sensitive films.
Innovation Solution
The proposed solution involves a humidity detecting device with a configuration that includes a sensor chip and an ASIC chip, utilizing a moisture-sensitive film between electrodes, where a drive signal is alternately inverted between two periods to convert charge into voltage, and a difference processing unit to cancel out leakage currents and reduce parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a charge amplifier is used to convert charge into voltage, then the humidity measurement function is achieved, but parasitic capacitance and leakage currents reduce measurement precision
Solution Approach 1:
The patent applies periodic action by using alternating drive signals to periodically switch between sampling the sensor capacitor and reference capacitor. This periodic switching allows the system to measure both capacitors under identical conditions and subtract their values, canceling out parasitic capacitance and leakage current effects that are common to both measurements.
Solution Approach 2:
The patent changes the drive signal parameter from DC to alternating signals with different phases. By applying alternating drive signals to the sensor and reference capacitors and measuring the difference in their charge-to-voltage conversion outputs, the system eliminates the impact of parasitic capacitance and leakage currents on measurement precision.
2Reliability
If capacitance-type humidity sensors with moisture-sensitive films are used, then humidity detection capability is provided, but power consumption increases
Solution Approach 1:
The patent reduces power consumption by using periodic measurement cycles instead of continuous measurement. The alternating drive signals are applied only during specific time periods to charge and measure the capacitors, rather than maintaining continuous drive signals, thereby reducing overall power consumption while maintaining reliable humidity detection capability.
3Measurement precision
If sensor unit and reference unit are arranged together on substrate, then measurement function is achieved, but device complexity increases
Solution Approach 1:
The patent merges the sensor unit and reference unit onto a single substrate, integrating both capacitance measurement functions into one device. This combining approach enables differential measurement to cancel parasitic effects while maintaining a compact, unified device structure rather than requiring separate devices.
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 configuration enhances the accuracy and efficiency of humidity measurement by minimizing the impact of parasitic capacitance and leakage currents, while reducing power consumption, leading to improved reliability and precision in humidity detection.
Implementation Method 1
a moisture sensitive film is used as a dielectric substance, the moisture sensitive film being formed of a high polymer material of which a permittivity changes according to an amount of absorbed water
Implementation Method 2
a high polymer material of which a permittivity changes according to an amount of absorbed water
Implementation Method 3
a charge amplifier... configured to convert an electric charge carried from the sensor unit into a voltage
Implementation Method 4
a drive circuit that drives the sensor unit in accordance with an alternating current (AC) drive signal as a square wave
Data Source
AI summary
A switched capacitor circuit includes a first charge-to-voltage converter including a first capacitor to operate in a first period to convert a first charge into a first output voltage. The switched capacitor circuit includes a second charge-to-voltage converter including a second capacitor to operate in a second period to convert a second charge into a second output voltage, the second period being different from the first period. The switched capacitor circuit includes a shield interconnect disposed between the first capacitor and the second capacitor, the shield interconnect having a constant potential.