Sensor Side Charge Cancellation for Capacitive Shadowing
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Solution Overview
Problem
Capacitive sensor devices face the issue of shadowing effects due to input objects with large RC time constants, leading to incorrect reporting of input objects or their size and position, as the increased capacitance causes measurements to reflect changes at other positions, mistaken for additional input objects.
Innovation Solution
The solution involves injecting a compensating charge onto the receiver electrode at a non-overlapping time, reducing the net charge subject to the RC time product, thereby minimizing or eliminating shadowing effects by canceling a portion of the charge on the receiver electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensor devices use standard measurement methods, then the device structure remains simple, but shadowing effects occur due to large RC time constants causing incorrect reporting of input objects
Solution Approach 1:
The system performs preliminary charge injection onto the receiver electrode before the actual measurement phase. This preliminary action compensates for the RC time constant effects in advance, allowing the subsequent measurement to accurately reflect only the input object's capacitive influence without shadowing effects from residual charges.
Solution Approach 2:
The measurement process is divided into periodic phases: a charge injection phase followed by a measurement phase. By periodically alternating between injecting compensating charge and performing measurements, the system eliminates shadowing effects while maintaining simple hardware architecture.
2Productivity
If charge is injected onto the receiver electrode during the same time period as measurement, then the process is efficient, but the injected charge interferes with the measurement signal
Solution Approach 1:
The time period is segmented into distinct phases: a charge injection time period and a measurement time period. By separating these functions temporally, the system prevents interference between the injected charge and the measurement signal, ensuring accurate detection while maintaining operational efficiency.
Solution Approach 2:
The system applies preliminary anti-action by injecting compensating charge in advance during a dedicated injection phase before the measurement phase begins. This timing arrangement ensures the compensating charge is in place to counteract RC effects without interfering with the subsequent measurement of the input object's signal.
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 reduces the effects of the RC time constant, resulting in more accurate detection of input objects without false reporting, enhancing the precision of positional information determination in capacitive sensor devices.
Implementation Method 1
capacitive sensor device determines the presence, location and/or motion of one or more input objects
Implementation Method 2
receive a resulting signal with the at least one receiver electrode during a third time period. The resulting signal includes effects corresponding to the injected charge and the transmitter signal
Data Source
AI summary
An input device includes a receiver electrode, a transmitter electrode and a processing system coupled to the receiver electrode and transmitter electrode. The processing system is configured to transmit a transmitter signal with the transmitter electrode during a first time period, inject a charge onto the receiver electrode during a second time period, and receive a resulting signal from the receiver electrode during a third time period. The resulting signal includes effects corresponding to the injected charge. The second time period and the third time period are non-overlapping.