Digital Driving Circuits for LCD Displays Using Pulse Density Modulation

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Solution Overview

Problem

Conventional LCD display control systems require complex and costly analog circuits to generate multiple voltage levels, which are expensive in terms of integrated circuit die area and power, and are inflexible for adding more commons or segments.

Innovation Solution

A digital signal-based system that uses pulse density modulation and inherent capacitance and resistance of the display to generate voltage levels, eliminating the need for analog circuits and allowing for scalable and efficient control of LCD segments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional analog circuits are used to generate multiple voltage levels, then the display segments can be properly driven, but the integrated circuit die area and power consumption increase significantly

Engineering Contradiction:

Improvedisplay segment driving capabilityVSAvoidintegrated circuit die area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent replaces complex analog voltage generation circuits with a digital control system. A single high bias voltage is generated using simple analog circuitry, then digitally modulated through pulse width modulation (PWM) to create multiple effective voltage levels. This substitution of digital for analog control dramatically reduces the die area required while maintaining the ability to drive multiple display segments at different brightness levels.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameter from direct analog voltage levels to digital pulse width modulation duty cycles. By varying the duty cycle of PWM signals, the effective voltage applied to display segments is controlled digitally. This parameter transformation allows a single analog voltage source to effectively generate multiple voltage levels through digital control, reducing hardware complexity and die area.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If multiple analog voltage levels are generated using resistor ladders, then the required voltage divisions are achieved, but the device complexity and manufacturing cost increase

Engineering Contradiction:

Improvevoltage level generationVSAvoidanalog circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces complex resistor ladder networks and analog voltage dividers with a digital PWM control system. Instead of using multiple precision resistors to create voltage divisions, the system uses a single high bias voltage source combined with digital pulse width modulation to achieve the same effective voltage control. This substitution eliminates the need for complex analog voltage division circuitry and reduces manufacturing complexity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates a universal control system where a single high bias voltage source and PWM controller can generate multiple effective voltage levels for different display segments. This multi-functional approach allows the same hardware to serve multiple purposes (driving multiple commons and segments with different brightness requirements) without requiring separate analog voltage generation circuits for each segment.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Illumination intensity

If the display is driven with high current, then the segment brightness is sufficient, but power consumption increases

Engineering Contradiction:

Improvesegment brightnessVSAvoidpower consumption

Core Design Contradiction:

Illumination intensityVSUse of energy by moving object

Solution Approach 1:

The patent employs pulse width modulation (PWM) to control display segment brightness. Instead of applying continuous high current, the system applies periodic pulses with varying duty cycles. The human eye perceives the average brightness of these pulsed signals, allowing high brightness perception during the active portion of the pulse while keeping the average power consumption lower. This periodic action enables brightness control without proportionally increasing continuous power consumption.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS9852702B2Digital driving circuits, methods and systems for display devices

Publication Date: 2017.12.26 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

A method may include generating display driver signals that vary between only two levels and applying the display driver signals to opposing electrodes of a display segment within a display device. An intrinsic capacitance of the display device filters the display driver signals to generate different analog signal levels at the display segment of the display device. The method varies the pulse density of the display driver signals to select or de-select the display segment based on an average voltage magnitude across the display segment over a time period. The display segment is activated when the average voltage magnitude exceeds a threshold value.