Low Voltage LCD Driver with Level Shifter and Segmented Switching
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Solution Overview
Problem
Existing low voltage drivers for high voltage LCDs face challenges in providing sufficient RMS voltage for good contrast across temperature ranges, especially at lower supply voltages like 3.6V, which limits their performance at cold temperatures and increases costs and chip area requirements.
Innovation Solution
A low voltage driver design incorporating an input transistor switching circuit, output transistor switching circuit, level shifter, and logic circuit that selects and applies bias voltages to limit voltage across transistor junctions to prevent breakdown, enabling high voltage operation while reducing power consumption and chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a 3.6V supply voltage is used for the LCD driver, then power consumption and chip area are reduced, but the RMS voltage output is insufficient for good contrast at cold temperatures
Solution Approach 1:
The patent changes the voltage level parameter by using a voltage boosting circuit to convert the 3.6V supply voltage into higher voltage levels (5V or 10V) for LCD drive output. This allows the driver to maintain low power consumption at 3.6V while delivering sufficient RMS voltage for good contrast across the temperature range by operating the LCD at elevated voltage levels.
2Reliability
If a 5V supply voltage is used for the LCD driver, then sufficient RMS voltage is provided for good contrast across temperature ranges, but power consumption and chip area increase
Solution Approach 1:
The patent dynamically changes the output voltage parameter based on temperature conditions. The voltage boosting circuit is enabled to provide 5V or 10V output when high RMS voltage is needed for cold temperature operation, while allowing 3.6V operation when sufficient contrast is achieved, thus optimizing power consumption across different operating conditions.
3Reliability
If high voltage levels (5V or 10V) are used for LCD drive output, then sufficient RMS voltage is achieved for good contrast, but transistor breakdown occurs due to excessive voltage across junctions
Solution Approach 1:
The patent segments the voltage handling functions into distinct stages: a low-voltage logic circuit operating at 3.6V that generates control signals, and a separate voltage boosting circuit that converts this low-voltage control into high-voltage drive signals (5V or 10V) for the LCD. This segmentation allows the logic transistors to operate safely at low voltage while still achieving high voltage output for good contrast.
Solution Approach 2:
The patent introduces a voltage boosting circuit as an intermediary between the low-voltage logic circuit and the high-voltage LCD drive output. This intermediary circuit performs the voltage conversion function, isolating the sensitive logic transistors from high voltage stress while enabling sufficient RMS voltage delivery to the LCD for good contrast across temperature ranges.
Data Source
AI summary
A low voltage driver for a higher voltage LCD includes a plurality of LCD drive bias voltage input-terminals; an LCD drive voltage output terminal; an input transistor switching circuit having at least one switch for each LCD drive bias voltage for selecting one of the bias voltages; an output transistor switching circuit, responsive to the input transistor switching circuit, for applying the selected one of the bias voltages to the LCD drive voltage output terminal, the transistors of the switching circuits having a predetermined breakdown voltage; a level shifter for providing switching voltages counterpart to the plurality of bias voltages; a logic circuit for enabling the first transistor switching circuit to select a one of the bias voltages and applying a set of counterpart switching voltages to the input and output transistor switching circuits for connecting the selected one of the bias voltages to the output terminal and applying a set of switching voltages to the input and output switching circuits which limit the voltage across the transistor junctions in the switching circuit to less than the predetermined breakdown voltage.