Capacitive Discharge Circuit for Touch Screen Flicker Noise

Solution Overview

Problem

Existing methods for discharging parasitic capacitances in touch sensitive screens suffer from flicker noise due to the use of transistors that source current, which affects the accuracy of input recognition on handheld electronic devices.

Innovation Solution

A capacitive discharge circuit comprising a switched capacitor circuit, a voltage regulator circuit, and a controller that operates in multiple phases to charge and discharge capacitors, sharing charge between the line and the capacitor to effectively discharge parasitic capacitances without using transistors that source current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If transistors that source current are used to discharge parasitic capacitances, then the discharge function is achieved, but flicker noise is generated which reduces input recognition accuracy

Engineering Contradiction:

Improveinput recognition accuracyVSAvoidflicker noise

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes the harmful element (current-sourcing transistor) from the discharge circuit. Instead of using a transistor to source current for discharge, the invention uses a current-sinking transistor in conjunction with a capacitor to achieve discharge without the flicker noise generated by current-sourcing transistors, thereby eliminating the harmful factor while maintaining the discharge function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional approach by using a current-sinking transistor instead of a current-sourcing transistor. Rather than actively pushing current to discharge the parasitic capacitance, the invention creates a path that allows current to sink naturally through the capacitor and transistor combination, reversing the traditional discharge mechanism to avoid flicker noise.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If transistors that source current are used to discharge parasitic capacitances, then the discharge function is achieved, but the dynamic range and sensitivity of the touch screen are reduced

Engineering Contradiction:

Improvetouch screen sensitivityVSAvoidflicker noise

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes the harmful element (current-sourcing transistor) from the discharge circuit. Instead of using a transistor to source current for discharge, the invention uses a current-sinking transistor in conjunction with a capacitor to achieve discharge without the flicker noise generated by current-sourcing transistors, thereby eliminating the harmful factor while maintaining the discharge function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional approach by using a current-sinking transistor instead of a current-sourcing transistor. Rather than actively pushing current to discharge the parasitic capacitance, the invention creates a path that allows current to sink naturally through the capacitor and transistor combination, reversing the traditional discharge mechanism to avoid flicker noise.

Inventive Principle:

Principle #13The other way round (Inversion)

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 discharges parasitic capacitances, enhancing the accuracy of touch input recognition by minimizing flicker noise and improving the dynamic range and sensitivity of touch sensitive screens.

Implementation Method 1

a capacitor having first and second terminals... in a first phase, charge the capacitor by coupling the capacitor between a common mode node and a power supply node... in a second phase, discharge the capacitor by coupling the voltage regulator circuit in series with the capacitor between the power supply node and a ground node

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a voltage regulator circuit coupled between the switched capacitor circuit and the switched circuit... in a second phase, discharge the capacitor by coupling the voltage regulator circuit in series with the capacitor between the power supply node and a ground node

Methodology Applied

Scientific EffectVoltage regulation:

Data Source

PatentUS10534489B2Capacitive discharge circuit for touch sensitive screen

Publication Date: 2020.01.14 STMICROELECTRONICS INT NV

AI summary

A capacitive discharge circuit includes a line having a capacitance, a switched capacitor circuit including a capacitor, a switched circuit coupled to the line, and a voltage regulator coupled between the switched capacitor circuit and the switched circuit. A controller operates the switched capacitor circuit and switched circuit to in a first phase, charge the capacitor by coupling the capacitor between a common mode and a power supply, and in a second phase, discharge the capacitor by coupling the voltage regulator in series with the capacitor between the power supply node a ground. The controller is also configured to in a third phase, charge the capacitor by coupling the capacitor between the common mode and the power supply, and in a fourth phase, share charge between the line and the capacitor by coupling the voltage regulator and the capacitor in series between the line and the ground.