Passive-matrix:

• LCDs use a simple grid to supply the charge to a particular pixel on the display. Creating the grid is quite a process.
• It starts with two glass layers called substrates. One substrate is given columns and the other is given rows made from a transparent conductive material. This is usually indium-tin oxide.
• The rows or columns are connected to integrated circuits that control when a charge is sent down a particular column or row.
• The liquid crystal material is sandwiched between the two glass substrates, and a polarizing film is added to the outer side of each substrate.
• To turn on a pixel, the integrated circuit sends a charge down the correct column of one substrate and a ground activated on the correct row of the other.
• The row and column intersect at the designated pixel, and that delivers the voltage to untwist the liquid crystals at that pixel.
• The simplicity of the passive-matrix system is beautiful, but it has significant drawbacks, notably slow response time and imprecise voltage control.
• Response time refers to the LCD's ability to refresh the image displayed.

Active-matrix:

• LCDs depend on thin film transistors (TFT). Basically, TFTs are tiny switching transistors and capacitors. They are arranged in a matrix on a glass substrate.
• To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge.
• The capacitor is able to hold the charge until the next refresh cycle. And if we carefully control the amount of voltage supplied to a crystal, we can make it untwist only enough to allow some light through.
• By doing this in very exact, very small increments, LCDs can create a gray scale. Most displays today offer 256 levels of brightness per pixel.