Capacitive Touchscreen Charge Acquisition Circuit for IC Area Reduction
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Solution Overview
Problem
Current capacitive sensing technologies in touchscreens require large feedback capacitors and active current division circuits, which increase area requirements and reduce operational stability, especially in large touchscreen systems.
Innovation Solution
A capacitive touchscreen system with a charge acquisition circuit comprising a bank of capacitors arranged in parallel, connected to both drive and sense electrodes, allowing for the transfer of input signals representing mutual and stray capacitances, and a charge integrator circuit, which reduces the need for large feedback capacitors and active current division circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional charge integrator readout circuits with increased feedback capacitor values are used to handle increased dynamic range of charge signals, then the dynamic range capability is improved, but the integrated circuit area increases significantly
Solution Approach 1:
The patent segments the charge signal handling into two distinct stages: a charge acquisition stage that captures the full dynamic range signal from multiple driven electrodes, and a charge integration stage that processes the signal in controlled increments. This segmentation allows the feedback capacitor to remain small while still handling large dynamic range signals through the two-stage approach.
Solution Approach 2:
The charge acquisition circuit performs preliminary charge capture and storage before the integration stage processes the signal. By pre-capturing the charge on acquisition capacitors in parallel, the system prepares the signal for integration without requiring the feedback capacitor to immediately handle the full dynamic range, thus reducing the required feedback capacitor size.
2Area of stationary object
If active current division circuits are used to reduce feedback capacitor size, then the feedback capacitor area is reduced, but operational and temperature stability decreases
Solution Approach 1:
The patent replaces active current division circuits (which use amplifiers and resistors) with a passive charge acquisition circuit using capacitors and switches. This substitution eliminates the use of operationally and temperature-sensitive components (amplifiers and resistors) while maintaining the ability to reduce feedback capacitor size, thus improving stability.
Solution Approach 2:
The patent changes the operational parameters by using a two-stage charge transfer process instead of continuous current division. The charge acquisition stage captures signals at one voltage level, then transfers the charge to the integration stage, allowing the feedback capacitor to operate at lower effective values while maintaining accuracy through the controlled charge transfer process.
3Object-affected harmful factors
If multiple drive electrodes are driven simultaneously to increase touch signal noise immunity, then noise immunity is improved, but the dynamic range of charge signals increases requiring larger feedback capacitors
Solution Approach 1:
The patent segments the charge handling into acquisition and integration stages, allowing multiple drive electrodes to be driven simultaneously for improved noise immunity while the segmented architecture prevents the need for proportionally larger feedback capacitors.
Solution Approach 2:
The charge acquisition circuit acts as an intermediary between the drive electrodes and the charge integrator. It captures the combined charge signals from multiple driven electrodes and transfers them in a controlled manner to the integration stage, mediating the dynamic range issue and allowing the feedback capacitor to remain small.
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 solution reduces power consumption, increases operational stability, and minimizes integrated circuit area while maintaining high accuracy for multi-touch measurements, eliminating the need for large feedback capacitors and active current division circuits.
Implementation Method 1
a charge acquisition circuit comprising a plurality of capacitors arranged in parallel respecting one another, first input switches and second output switches corresponding to each of the capacitors in the charge acquisition circuit
Data Source
AI summary
Disclosed herein are various embodiments of a capacitive touchscreen system which includes switchable charge acquisition circuits and corresponding charge integrator circuits for sensing mutual capacitances associated with a touchscreen. Various embodiments of the switchable charge acquisition circuits and corresponding charge integrator circuits provide lower power consumption, increased operational stability, substantially reduced integrated circuit area, and increased temperature stability.