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MCC141537

LCD Segment / Common Driver with Controller

Motorola => Freescale 

LCD Drive Voltage Generator

This module generates the LCD voltages needed for display output.

This section should take a single supply input and generate necessary

bias voltage.

It consists of :

1. Voltage Doubler and Voltage Tripler

To generate the Vcc voltage. Doubler is used for LCD panel which

needs lower driving voltage for less power consumption. Tripler is

used for LCD panel which needs higher driving voltage.

2. Voltage Regulator

Feedback gain control for initial LCD display voltage. One can also

use it as an external contrast control.

3. Voltage Divider

Divide the LCD display voltage (VLL2-VLL6) from the regulator out-

put. This is a low power consumption circuit which consumes very

little ILCD current compare with traditional resistor ladder method.

4. Self adjust temperature compensation circuitry

Provide 4 different compensation grade selections to satisfy the

various liquid crystal temperature grades. This temperature coeffi-

cients can be selected by software control.

5. Contrast Control Block

Software control of 16 voltage levels of LCD display voltage.

All blocks can be individually turned off if external voltage generator

is provided.

16 Bit Latch / 120 Bit Latch

A 136 bit long register which carries the display signal information.

First 16 bits are Common driving signals and other 120 bits are Seg-

ment driving signals. Data will be input to the Level Shifter for bumping

up to the required level.

Level Selector

Level selector is a control of the display synchronization. Display volt-

age can be separated into two sets and used with different cycle. Syn-

chronization is important since it selects the required LCD voltage level

to the HV Buffer Cell for output signal voltage pump.

HV Buffer Cell (Level Shifter)

HV buffer cell works as a level shifter which translates the low voltage

output signal to the required driving voltage. The output is shifted out

with a internal FRM clock which comes from the Display Timing Gener-

ator. The voltage levels are determined by the level selector which is

synchronized with the internal M signal.

LCD Panel Driving Waveform

This is an example of how the Common and Segment drivers may

be connected to a LCD panel. The waveform shown in figure 7a, 7b and

7c illustrates the desired multiplex scheme.

Com0

Com1

Com2

Com3

Com4

Com5

Com6

Com7

Figure 7a. LCD Display Waveform

MC141537

3-110

MOTOROLA

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