Electronic – Why multiple bias voltages are required to drive LCD

biaslcd

I have read this document:
AN658 – LCD Fundamentals and the LCD Driver Module of 8-Bit PIC® Microcontrollers

I understand that the main concern is to maintain 0 Vdc bias on every pixel when driving LCD display.

But I do not understand why there are multiple bias voltages required to drive backplanes (= common nodes).

Why are required such crazy unintuitive waveforms?
enter image description here

Why I can't use just static biasing?
For example when I want to make 1 pixel on:
1st frame would be BP0=1 (common), SEG0=0, the 2nd frame would be BP0=0 (common), SEG0=1. This would make 0 Vdc bias and the pixel would have the maximal contrast.

Best Answer

Voltage at particular segment is a difference between voltage on two electrodes, lets call them row and column. There are 4 (four!!) cases:

  • Active segment in active row: |Vactivecol - Vactiverow| = Vmax.
  • Nonactive segment in active row |Vactiverow - Vnotcol| = 1/3 Vmax.
  • Nonactive segment in nonactive row while this segment column electrode is active |Vactivecol - Vnotrov| = 1/3 Vmax.
  • Nonactive segment in nonactive row |Vnotcol - Vnotrow| = 1/3 Vmax.