LCD Common Voltage Generator Using Tunable Constant-Resistance DAC
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Solution Overview
Problem
Existing common voltage generator circuits for liquid crystal displays are inefficient due to high die area and power consumption, and introduce offset voltages that degrade accuracy and control, making precise digitally controlled voltage generation challenging.
Innovation Solution
A digitally controlled voltage generator using a constant resistance digital-to-analog converter (DAC) with tunable bias resistors, eliminating the need for an operational amplifier and allowing compensation for parasitic resistances, is employed to generate a common voltage for LCD panels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an operational amplifier is used in the voltage generator circuit, then the circuit can provide voltage amplification and buffering, but the die area and power consumption increase significantly
Solution Approach 1:
The patent removes the operational amplifier from the voltage generator circuit, extracting the problematic component that caused high power consumption and large die area. The circuit is reconfigured to function without this active component, using only passive elements (resistors and capacitors) to achieve the voltage generation function.
Solution Approach 2:
The patent replaces the expensive and power-hungry operational amplifier with simple, low-cost passive components (resistors and capacitors). This substitution uses inexpensive elements that consume minimal power while still achieving the desired circuit functionality.
2Measurement precision
If an operational amplifier is used in the voltage generator circuit, then voltage buffering can be achieved, but offset voltages are introduced that degrade accuracy
Solution Approach 1:
The patent extracts and removes the operational amplifier that introduces offset voltages. By eliminating this active component, the source of offset voltage errors is removed, thereby improving voltage control accuracy without the harmful side effects of amplifier offset.
Solution Approach 2:
The patent creates a simplified version of the voltage buffering function using passive RC circuits that replicates the essential buffering capability without the offset voltage problems of operational amplifiers. The passive circuit copies the functional behavior while avoiding the defects.
3Measurement precision
If fixed resistor values are used in the DAC circuit, then the circuit is simple to manufacture, but parasitic resistances cause voltage inaccuracies
Solution Approach 1:
The patent introduces tunable/adjustable resistors instead of fixed resistors, making the circuit parameters dynamic rather than static. This allows the resistors to be adjusted after fabrication to compensate for parasitic effects, achieving high accuracy without requiring extremely precise initial manufacturing.
Solution Approach 2:
The patent implements a feedback mechanism where the output voltage is measured and used to adjust the resistor values to compensate for parasitic resistances. This closed-loop approach ensures that voltage inaccuracies caused by parasitic elements are corrected, maintaining high accuracy despite manufacturing variations.
Data Source
AI summary
A digitally controlled voltage generator is disclosed for use in applications requiring fine resolution voltage control, such as generating a common voltage for a liquid crystal display. A constant resistance digital to analog converter (DAC) is configured to provide appropriate voltage steps by tuning bias resistors to generate desirable reference voltages for the DAC. The bias resistors are configured to be tuned after placement and routing steps in an integrated circuit design.