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Negative voltage, contrast and display

Hi all,

can someone tell me what is the technique used in the display to adjust the contrast? Normally there's a negative voltage to make that but what happens when that voltage changes? Why a negative voltage is necessary?

I want to study the display technology. Can someone tell me some tutorial or web site with a lot of informations about this subject?

Reply to
pozz
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Well, here's a couple of places that you can start at...

Ah, Schtool! After a search at

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, they leave the URL in the window, unlike google. I did a search on "cathode-ray tube" (without the quotes) and on "CRT display" (also without the quotes) and a lot of the links that showed up sound like a very good introduction to CRT principles.

The short answer is that they use a negative voltage because it's a "tube". The electrons boil off of the cathode, and are attracted to the anode(s), just like any tube, but they have focusing (focussing?) electrodes to make a beam; but generally, the control grid will be more negative than the cathode, to regulate the rate of flow of electrons. This will have a DC bias, which sets the "brightness", or "intensity" level, and a control signal (the "video") which changes the intensity very quickly as the electron beam is scanned across the screen.

The "contrast" control actually controls the gain of the video amplifier - more variations in control grid voltage give more variations in intensity of the "flying spot".

Hope This Helps! Rich

Reply to
Rich Grise

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