Passive matrix addressing
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Passive matrix addressing is an addressing scheme used in earlier LCD displays, and may be used in future LCD displays. This is a matrix addressing scheme meaning that only n + m control signals are required to address a n × m display. A pixel in a passive matrix must maintain its state without active driving circuitry until it can be refreshed again.
A new display technology uses a bi-stable pixel, which maintains its state indefinitely without the need for individual transistor elements at each pixel.
The signal is divided into a row or select signal and a column or video signal. The select voltage determines the row that is being addressed and all m pixels on a row are addressed simultaneously. When pixels on a row are being addressed, a Vsel potential is applied, and all other rows are unselected with a Vunsel potential. The video signal or column potential is then applied with a potential for each m columns individually. An on-lighted pixel corresponds to a Von, an off-switched corresponds to a Voff potential.
The potential across pixel at selected row i and column j is
- Vij = Vsel − Von | off
and
- Vij = Vunsel − Von | off
for the unselected rows.
Passive matrix addressed displays such as ferroelectric Liquid crystal display do not need the switch-component of an active matrix display because it has a built-in bistability. Technology for electronic papers also have a form of bistability. Displays with bistable pixel elements are addressed with passive matrix addressing scheme, where as TFT-LCD-displays are addressed using active addressing.
