Passive matrix addressing
Passive matrix addressing is an addressing scheme used in early LCD displays. This is a matrix addressing scheme meaning that only m + n control signals are required to address an m × n display. A pixel in a passive matrix must maintain its state without active driving circuitry until it can be refreshed again.
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 n 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
and
for the unselected rows.
Passive matrix addressed displays such as Ferro Liquid Display do not need the switch component of an active matrix display because they have built-in bistability. Technology for electronic paper also has a form of bistability. Displays with bistable pixel elements are addressed with a passive matrix addressing scheme, whereas TFT LCD displays are addressed using active addressing.