Capacitive Pen Detection Under Low Ground Mass Conditions
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Solution Overview
Problem
Capacitive pen detection fails in low ground mass conditions due to the user's palm and pen receiving the same signal, resulting in zero signal difference and failure to transmit capacitive pen signals, which leads to undetected inputs.
Innovation Solution
The input device employs sensor circuitry to determine when it is in a low ground mass state and drives specific groups of sensor electrodes with inverted or non-inverted signals and static DC voltage to maximize signal differences, enabling quicker detection of capacitive pens under these conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the proximity sensor device transmits uplink signals using conventional capacitive sensing, then the device can detect input objects normally, but the detection fails when the user's palm and capacitive pen tip receive the same signal, resulting in zero signal difference
Solution Approach 1:
The sensor array is divided into multiple independently controllable regions or groups of sensor electrodes. By segmenting the sensing area, the system can apply different drive signals to different segments, allowing the capacitive pen to receive an uplink signal while the palm receives a different signal, thus avoiding signal cancellation and enabling reliable detection even when both are present.
2Measurement precision
If the capacitive pen uses the pen body as reference to detect uplink signals, then the pen can detect signals normally, but the detection circuit cannot distinguish the pen signal from the palm signal when both receive the same uplink signal
Solution Approach 1:
Different regions of the sensor array are assigned different drive signal characteristics (e.g., different phases, amplitudes, or signal patterns). This local differentiation allows the capacitive pen, which contacts a specific region, to receive a unique uplink signal that can be distinguished from the palm signal by the detection circuit, thereby maintaining measurement precision and preventing information loss.
3Adaptability or versatility
If the proximity sensor device uses conventional uniform drive signals for all sensor electrodes, then the device structure remains simple, but the system cannot distinguish between palm and pen inputs when both are present in the sensing region
Solution Approach 1:
The drive signals for different sensor electrode regions are made dynamic and adjustable rather than static and uniform. The system can adaptively modify the drive signal characteristics based on detected input conditions, enabling the device to distinguish between palm and pen inputs while maintaining manageable complexity through controlled adaptability.
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 latency in detecting capacitive pens by maximizing signal differences, allowing for accurate detection even when the user's palm reaches the sensor surface before or simultaneously with the pen, improving input recognition.
Implementation Method 1
The capacitive pen transmits the capacitive pen signals responsive to the capacitive pen detecting an uplink signal from the proximity sensor device. The proximity sensor device transmits the uplink signal that a sensor in the tip of a capacitive pen detects.
Implementation Method 2
The detection circuit in the capacitive pen uses the body of the capacitive pen as a reference. Namely, the detection circuit detects the uplink signal based on the difference between signals from the capacitive pen tip and the capacitive pen body.
Implementation Method 3
when a proximity sensor device transmits the uplink signal and the user's palm is in the sensing region, both the palm of a user's hand and the capacitive pen tip receive the same signal. As a result, the user's palm couples the same uplink signal to the capacitive pen body
Data Source
AI summary
A processing system configured to detect an input object proximate the processing system. The processing system includes sensor circuitry configured to make a determination, when the processing system is in a low ground mass (LGM) state, that a large object is proximate to sensor electrodes of the processing system. The sensor circuitry is further configured, in response to a determination that a large object is proximate the sensor electrodes while the processing system is in the LGM state, to drive a first group of sensor electrodes with one of an inverted signal or a non-inverted signal and drive a second group of sensor electrodes with a static DC voltage.