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Liquid Crystal Multiplexing with Time Gap

IP.com Disclosure Number: IPCOM000079898D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Magdo, S: AUTHOR

Abstract

Liquid crystal multiplexing at high speeds of around 0.2 millisecond pulses, requires the use of voltages in the 20 to 40 volt range to energize the liquid crystals.

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Liquid Crystal Multiplexing with Time Gap

Liquid crystal multiplexing at high speeds of around 0.2 millisecond pulses, requires the use of voltages in the 20 to 40 volt range to energize the liquid crystals.

It is necessary to insure that a partial-select voltage cannot under any set of data conditions, remain across the crystal for several pulse lengths; otherwise a voltage of 6 or 7 volts applied for greater than 0.2 millisecond would be sufficient to illuminate the crystal. The present technique utilizes a time gap between each data pulse, during which both row and column voltages are 0 to eliminate the possibility.

Referring to the figure, the rows of liquid-crystal display 2 are scanned sequentially by strobe pulses having a duration delta t1 and amplitude Vs. Between the strobe pulses there is a delta t2 time gap. Data is fed to the column drivers a row at a time. Between the column pulses there is also a delta t2 time gap, so that during the time gap both the strobe and column voltages are 0.

As a result of this technique, neither the colunns nor the rows experience a pulse longer than delta t1 under worst-case conditions. Thus only a single threshold corresponding to delta t1 is applied. Without the time gap, a very long column pulse might appear under worst-case conditions, this could turn on the liquid-crystal element, if the pulse amplitude were higher than around 5 volts. This would limit the multiplexing ratio to around 1:10, whereas the present tech...