How does a CRT fire electrons at a screen with such accuracy?


So, I’ve been reading up on how a TV works – specifically, the older style ones. I’ve learned that they have a gun that fires electrons at the screen which ‘lights up’ the pixels because they are made of special materials. The thing that amazes me is how the electron gun can fire the electrons with such precision. The pixels are so close together. Does the gun physically move or is it done with magnets or something and if it is done with magnets how do they control the current precisely enough to fire each electron at the exact right place?

In: Technology

It does not aim the beam with such accuracy.

There are three electron beams. The beams come from different positions.
In between the beams and the display there is a mask that limits where the beams can hit.

This video demonstrates the mask with flashlights acting the part of beams: [These Are Not Pixels: Revisited]( (The mask part is at 7:10 but you can watch rest of it too)

CRT TV electron sources are stationary. The electron beam is deflected horizontally and vertically by specially-shaped electromagnet coils, controlled by a main circuit. That’s why wide CRT screens were very deep and needed a deep shelf.

The intensity of the electron beam at each part of the screen is based on the received analog picture signal. In the case of color CRT screens, there are 3 separate amplified signals, to control 3 separate electron beams, for red green and blue. These 3 color signals are generated in real-time, inside the TV’s circuitry, based on clever analog processing of the (one) incoming received signal.

The secret sauce is a precision manufactured grid screen with tiny holes. This grid sits between the electron source and the colored phosphor pixels that’re on the backside of the glass TV screen.

Given the manufactured angles and positions, each hole in the precision grid allows one of the 3 electron beams to pass to illuminate only the red phosphors, one electron beam to only illuminate the green phosphors, and one for only blue phosphors. Very accurate angles and positions of the screen, means the electron beam intensity does *not* need to change improbably fast, precisely, or be super focused. That allowed home VCRs to record TV broadcasts, albeit with fuzzier horizontal picture resolution and worse color resolution.

Still, analog data allowed quite a lot of information, so it took decades for digital computer technology to become fast enough to “catch up” to allow comparable frame rates and image resolution.