Saturday, 27 October 2018

How are DACs integrated in color LCD screens?


I'm having trouble imagining what actually happens inside an LCD screen.


I picture digital RGB data for each pixel getting sent to the screen through a connector. Lets say we have 24-bit color for each pixel, so 8 bits each for red, green, and blue subpixel. Inside the LCD, for each subpixel a voltage must be applied to control its intensity. This is where a DAC must come in to convert each 8 bit intensity value (digital) to a proportional voltage (analog). But, surely there is no DAC for every subpixel? My laptop screen is 1920x1080 so it has over 6 million subpixels.


So, how are these DACs integrated into the architecture of this LCD? How many DACs are in a single LCD screen?



I read that a transistor is used to select a particular liquid crystal cell and charge it/light it up, and a capacitor holds the charge briefly until the next refresh cycle. So that would eliminate the need for 6 million DACs, although it would mean you need 6 million transistors and capacitors. But I'm still wondering about these DACs - they never seem to get mentioned because people consider LCD screens "digital".




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