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Developing segment LCD drive firmware

Posted: 17 Feb 2010     Print Version  Bookmark and Share

Keywords:LCD drive  drive firmware  LCD drive applications 

Segment LCD drives can be found in everything from watches, home thermostats, portable medical instruments like glucose meters and blood pressure monitors, and even in certain automobiles. To meet the needs of these applications, nearly every MCU vendor provides devices with LCD drive capabilities.

And even as a mature technology, LCD drives continue to evolve, offering developments new and innovative capabilities. With integrated bias circuitry, individual pin muxing and mapping tools, developers can simplify and accelerate the design process while reduce system component count and cost.

A traditional LCD drive needs external R or C circuits to create a bias voltage. Almost all MCUs and SoCs can drive up to four commons. This usually requires 1/3 bias and so takes approximately four pins. Developers need to connect an external resistive ladder or capacitive network to these pins to generate the LCD bias.

Attempts have been made to integrate this resistor ladder inside the drive device. However, the resistor ladder should be optimised for a given display to achieve the best power and contrast. As a consequence, an integrated ladder will provide compromised performance for a typical display and may not meet requirements for all systems.

Alternatively, new LCD drives use a high-value resistor or programmable resistor ladder to optimise power and use a dynamically controlled buffer to solve drive strength issues. This buffer is automatically turned off to save power after the pixel voltage reaches the target voltage, and then a low drive strength output retains the state.

Implemented in this way, developers still have the ability to tune bias circuitry for optimal power and contrast while conserving pins on the device and avoiding the need for as many external components.

View the PDF document for more information.

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