The static driving technique is the basic driving of a LCD which has the advantage of needing fewer external support but needs lots of pins for the segments of the LCD and hence allows less dense design.
The idea
For each digit, each segment is directly connected to a pin. In order to save some pins, all the other electrodes of each segment is linked together into a common pin.
The example
Consider an LCD with two digits. It is composed of a front plane and a back plane. In the front pane, each segment of a digit is connected to a distinct pin as illustrated in Figure 1, remark the density of connections. In the back pane all the electrodes of all the digits are connected each other and finally to a common (com) pin as illustrated in Figure 2. Therefore, if we count pins, there are 8 pins per digit in the front pane, plus one pin for the back plane. Summing up with a formula, the number of pins is 8N+1, where N is the number of digits in the display.
Frame frequency and bias
LCD are AC devices and hence one must specify the AC frequency used. Frame frequency ranges between 20Hz and 200Hz. Below 20Hz, one might experience the refreshes of the LCD (recall that human eye can distinguish frames up to 18 frames/second). A frequency higher than 200Hz might cause problems with the capacitive elements of the LCD.
The bias is the number of voltage levels that are used. Indeed, in static driving only two levels are used, say V0 and V1. As an example, consider a given segment SEG. In oder to deduce the waveforms passing through the backpane COM and SEG, let us impose that VCOM - VSEG = 0 whenever SEG is unselected (see Figure 3). Since we should switch of value during the frame and there are only two possible values, then the waveform of SEG signal when SEG is selected, it is the complement of the signal unselected signal. As a consequence, when SEG is selected, the COM-SEG signal has a peak-to-peak amplitude equal to 2V1. See Figure 4.
The example
Consider an LCD with two digits. It is composed of a front plane and a back plane. In the front pane, each segment of a digit is connected to a distinct pin as illustrated in Figure 1, remark the density of connections. In the back pane all the electrodes of all the digits are connected each other and finally to a common (com) pin as illustrated in Figure 2. Therefore, if we count pins, there are 8 pins per digit in the front pane, plus one pin for the back plane. Summing up with a formula, the number of pins is 8N+1, where N is the number of digits in the display.
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| Figure 1. Front pane for two-digits LCD with static driving. |
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| Figure 2. Back pane for two-digits LCD with static driving. |
LCD are AC devices and hence one must specify the AC frequency used. Frame frequency ranges between 20Hz and 200Hz. Below 20Hz, one might experience the refreshes of the LCD (recall that human eye can distinguish frames up to 18 frames/second). A frequency higher than 200Hz might cause problems with the capacitive elements of the LCD.
The bias is the number of voltage levels that are used. Indeed, in static driving only two levels are used, say V0 and V1. As an example, consider a given segment SEG. In oder to deduce the waveforms passing through the backpane COM and SEG, let us impose that VCOM - VSEG = 0 whenever SEG is unselected (see Figure 3). Since we should switch of value during the frame and there are only two possible values, then the waveform of SEG signal when SEG is selected, it is the complement of the signal unselected signal. As a consequence, when SEG is selected, the COM-SEG signal has a peak-to-peak amplitude equal to 2V1. See Figure 4.
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| Figure 3. Waveforms when SEG is unselected. |
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| Figure 4. Waveforms when SEG is selected. |
LCD : the multiplexing technique
