Converting TTL monitor to Analog

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Thu May 10 11:29:02 2001

At 09:10 AM 5/10/01 -0600, Dick wrote:
> >
> > Color monitors have a color mask, and that color mask has a 'dot pitch'
> > which defines where you can display pixels. If you attempt to display more
> > pixels on a line than there are holes in the mask, then you will get
> > banding artifacts.
> >
>I've seen no evidence of this. If this were the case, then the fact that many
>display systems use inexpensive 1000 ppm oscillators would cause enough
>variation that it would be obvious on those monitors having this feature.
>Moreover, horizontal phase adjustment and vertical height/horizontal width
>adjustment would be impractical.

Evidence of what? The shadow mask or the interference patterns created by
displaying at something close to the dot pitch? Take a 17" monitor (13.5"
across) with a .28 dot pitch. That's about 91 dots per inch (25.4mm/inch /
0.28mm/dot) which gives a top resolution of 1228.5 dots. Now run it at 1280
x 1024, see the "moire" pattern. ? Now try it at 1600 x 1200, its even
weirder.

>Amplifier bandwidth issues are a factor in the practical use range of a given
>monitor. However, that has nothing to do with whether a monitor is analog or
>digital in nature.

All monitors are analog, they all have amplifiers to convert from the
user's video input into a voltage that can affect the brightness of the
electron beam. Now in "TTL" or "Digital" monitors there amplifiers respond
in a very non-linear way to the input. Thats the difference. Once it gets
to the actual video electronics they are darn near all the same.

Amplifier bandwidth will determine how "cleanly" the colors shift from one
to the next, colors are produced by a set of three intensities that in turn
become beam intensities, which in turn excite three phosphors to become
light intensity. There is also a frequency response component in the phosphor.

> >
> > You "can" drive monitors all over the map, eventually you will destroy them
> > if you allow the horizontal output driver to over heat. However, getting an
> > acceptable signal out of one is more constrained.
> >
>While that's true, it's hard to do.

Your correct of course, with 10 year old technology it is somewhat
difficult. With a modern video card for the PC its trivial.

--Chuck
Received on Thu May 10 2001 - 11:29:02 BST