Capacitance Sensing Circuit Using Pull-Up Currents for Fast Measurement
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Solution Overview
Problem
Existing capacitance sensing circuits face challenges in accurately and efficiently measuring small capacitance changes, such as those caused by a finger touch, due to long measurement periods, noise disturbance, and high power consumption.
Innovation Solution
A capacitance sensing circuit that applies pull-up currents during specific periods to rapidly change the voltage level at a capacitive device, allowing for a shorter measurement time and enabling accurate capacitance calculation, with the option to repeat measurements for enhanced reliability and using different current paths to optimize measurement speed and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a common capacitance sensing circuit with a pull-up resistor is used, then the capacitance can be measured, but the measurement period becomes long (40 to 500 microseconds)
Solution Approach 1:
The patent applies periodic action by using a clock signal to generate multiple sampling points within a reduced measurement period. The clock signal periodically switches the capacitive device between charging and discharging states, allowing the system to capture voltage changes at multiple discrete time points. This periodic sampling approach enables accurate capacitance measurement while significantly reducing the total measurement time compared to traditional continuous measurement methods.
2Measurement precision
If a long measurement period is used to ensure accurate capacitance measurement, then measurement accuracy is maintained, but noise disturbance and instability increase
Solution Approach 1:
The patent applies the skipping principle by rushing through the measurement process in a condensed time frame. Instead of allowing the voltage to naturally charge/discharge over a long period, the system uses a clock signal to force rapid switching between states, completing the measurement cycle much faster. This approach skips through the traditional slow measurement process, thereby reducing exposure to noise and instability while maintaining measurement accuracy through multiple rapid sampling points.
3Measurement precision
If a long measurement period is used, then capacitance can be accurately measured, but power consumption increases
Solution Approach 1:
The patent applies periodic action by using a clock signal to generate multiple sampling points within a reduced measurement period. The clock signal periodically switches the capacitive device between charging and discharging states, allowing the system to capture voltage changes at multiple discrete time points. This periodic sampling approach enables accurate capacitance measurement while significantly reducing the total measurement time compared to traditional continuous measurement methods.
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 significantly reduces the overall time required for capacitance sensing, enhances accuracy, suppresses noise, and lowers power consumption, making it suitable for real-time applications and small capacitance measurements.
Implementation Method 1
Electrical capacitance or capacity is the ability of a body to hold an electrical charge. It is also a measure of the amount of electric charge stored by a capacitive device for a given electric potential.
Implementation Method 2
whenever an electric voltage exists between two separated conductors, an electric field is present between those conductors
Data Source
AI summary
A capacitance sensing circuit comprises a capacitive device having a capacitance, the device initially being at a first voltage level. The capacitance sensing circuit is capable of applying one or more pull-up currents to the device during one or more corresponding pull-up periods of time, for changing the first voltage level into one or more corresponding pull-up voltage levels; applying a measurement current to the device; and measuring a measurement period of time, during which one of the pull-up voltage levels changes into a second voltage level. A method of sensing a capacitance of a capacitive device comprises applying a first voltage to the device; applying one or more pull-up currents during corresponding pull-up times, for changing the first voltage into corresponding pull-up voltages; applying a measurement current; and measuring a time, during which one pull-up voltage changes into a second voltage.