Passive matrix addressing

Passive matrix addressing is an addressing scheme used in early LCDs. 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 V_sel potential is applied, and all other rows are unselected with a V_unsel potential. The video signal or column potential is then applied with a potential for each m columns individually. An on-switched (lit) pixel corresponds to a V_on, an off-switched (unlit) corresponds to a V_off potential.^[1]

The potential across pixel at selected row i and column j is

${\displaystyle V_{ij}=V_{\mathit {sel}}-V_{\mathit {on|off}}}$

and

${\displaystyle V_{ij}=V_{\mathit {unsel}}-V_{\mathit {on|off}}}$

for the unselected rows.^[2]

This scheme has been expanded to define the limits of this type of addressing typical LCDs.^[3][4]

Passive matrix addressed displays, such as ferroelectric liquid crystal displays, 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.