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ADVANCED LOW POWER TECHNIQUES FOR SiM3L1XX DEVICES

Silicon Laboratories 

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5.4. LCD

For applications that use the LCD0 module, the SiM3L1xx devices have several features that help reduce power

consumption.

5.4.1. Segment Resetting

Each segment of an LCD can be modeled as a capacitor in the order of tens of pF. A typical load current is 1 nA per

segment per pF, so a 160-segment LCD with 50 pF per segment can draw 8 µA of load current. The SiM3L1xx

devices include a segment resetting feature to reduce this load current. Figure 7 illustrates the basic architecture

model of an LCD.

Segment

SEG0 SEG1 SEG2 SEG3 SEG4 SEG5 SEG6 SEG7

COM0

COM1

COM2

COM3

Figure 7. LCD Model

LCD segments are energized (i.e., turn opaque) by ac potential waveforms between the segment and the common

signal for that segment. These waveforms transition between 0 and 3 V, for example, which results in an amplitude

of –3 to 3 V on the segment, depending on the phase of the segment and common waveforms. Figure 9 shows an

example of the common waveforms for 4-mux mode.

To turn on a segment, the controller drives the segment to 3 V or 0 V when the common is driven to 0 V or 3 V,

which leads to ±3 V on the segment. To turn a segment off, the controller drives the segment to 1 V or 2 V when the

common signal is 0 V or 3 V, which leads to ±1 V on the segment.

Most LCD controllers transition directly from the most positive amplitude (3 V) to the most negative amplitude

(–3 V), as shown in Figure 8. This behavior leads to extra charge being pulled from the battery, since the battery

must drive a 6 V transition overall.

Segment

3V

3V

3V

3V

3V

3V

+3 V

+3 V

-3 V

Figure 8. Traditional LCD Segment Transition

Rev. 0.1

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