Capacitive Sensing Circuit Phase Control for Multi-Touch Noise Reduction
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Solution Overview
Problem
Existing capacitive sensing circuits for multi-touch panels face challenges in enhancing touch sensitivity due to low frequency noise components, which are difficult to remove effectively.
Innovation Solution
A capacitive sensing circuit design that includes a transmitting circuit, a receiving circuit with a charge integrating circuit based on a current mirror, and a control signal generator to detect capacitance changes using different phase modes, allowing for the determination of touch events by subtracting or averaging capacitance values, thereby improving touch sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional filters are used to remove noise components, then high frequency noise can be removed easily, but low frequency noise components remain difficult to remove
Solution Approach 1:
The sensing period is divided into multiple sub-periods (first through fourth sub-periods) with different phase combinations. By segmenting the measurement process into discrete phases and analyzing capacitance changes in each phase separately, the system can distinguish touch signals from low frequency noise through comparative analysis of phase-specific capacitance variations.
Solution Approach 2:
The system employs periodic phase switching of the driving signals applied to transmitter and receiver electrodes. By periodically changing the phase relationships between driving signals across multiple sub-periods and comparing the resulting capacitance measurements, the system creates a periodic measurement pattern that helps identify and eliminate low frequency noise components while preserving touch signal integrity.
2Measurement precision
If the charge integrating circuit operates in a single phase mode, then the circuit structure is simple, but the touch sensing sensitivity is reduced due to low frequency noise
Solution Approach 1:
The charge integrating circuit dynamically switches between multiple phase modes (first phase mode with opposite phase relationship, second phase mode with same phase relationship) during different sub-periods. This dynamic phase switching allows the system to collect capacitance data under varying phase conditions, enabling noise rejection through comparative analysis while maintaining a relatively simple circuit structure that can adapt its operating state.
Solution Approach 2:
The system changes the phase relationship parameter between driving signals applied to transmitter and receiver electrodes. By varying this phase parameter across different sub-periods (opposite phase in first phase mode, same phase in second phase mode), the system creates different measurement conditions that help distinguish touch signals from low frequency noise, thereby improving sensitivity without requiring complex hardware modifications.
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 effectively increases touch sensing sensitivity by accurately detecting touch positions and reducing the impact of low frequency noise components, enhancing the overall performance of multi-touch panels.
Implementation Method 1
The transmitting circuit part is connected to a transmitting line of the multi-touch panel to supply a transmitting signal of a rectangular wave to the transmitting line
Implementation Method 2
detect a difference of a capacitance generated between the transmitting line and the receiving line
Implementation Method 3
The receiving circuit part includes a charge integrating circuit based on a current mirror integrating each charge in correspondence with a rising period and a falling period of the transmitting signal
Implementation Method 4
The control signal generator outputs a first integral control signal and a second integral control signal that are mutually opposite to each other. The control signal generator outputs the first integral control signal having an opposite phase to the transmitting signal and the second integral control signal having the same phase as the transmitting signal
Implementation Method 5
The touch determining part determines whether or not a touch is generated based on a capacitance value detected in accordance with the first phase mode and a capacitance value detected in accordance with the second phase mode
Data Source
AI summary
A capacitive sensing circuit for a multi-touch panel includes a transmitting circuit configured to supply a transmitting signal to a transmitting line; and a receiving circuit part configured to detect a difference of a capacitance between the transmitting line and a receiving line. A control signal generator in the capacitive sensing circuit is configured to output first and second integral control signals respectively having an opposite phase to and the same phase as the transmitting signal in a first phase mode, and to output the first and second integral control signals respectively having the same phase as and an opposite phase to the transmitting signal in a second phase mode. The first and second integral control signals are mutually opposite to each other. A touch determining part is configured to determine whether a touch is generated based on capacitance values detected in the first and second phase modes.