Re: Automatic voltage scaling with op-amp?

From: Glenn Gundlach (stratus46_at_yahoo.com)
Date: 09/20/04 

Date: 19 Sep 2004 21:52:45 -0700

fozztexx@fozztexx.com (Chris Osborn) wrote in message news:<Mcl3d.22990$qO5.13386@newssvr29.news.prodigy.com>...
> I recently got a grab bag of parts from an electronics supplier. I was
> going through the chips I got and I'm wondering if any of them might
> be of any use in making a circuit that can automatically scale a 15khz
> video signal from 0V-n (never more than 3V) to the 0V-0.7V that a
> normal RGB monitor uses.
>
> I think I have a whole bunch of LM311 op-amps. I found a circuit on
> the net that shows how to use an op-amp as a peak detector. I thought
> I could use the peak detector as some sort of input for the maximum of
> the input video signal, and then somehow use 0.7 as the maximum of the
> output, and then an op-amp could scale it. Obviously I'll have to
> build 3 such circuits, one each for red, green, and blue.
>
> But... I have no idea how to do it. I can't find any schematics on the
> net which do anything similar.

I'm afraid your LM311s are not opamps but voltage comparators. You can
see the datasheet here
http://www.fairchildsemi.com/ds/LM/LM311.pdf
As for gain scaling of video, the video level is not a good way to do
it since its hard to tell what levels should be until you get a peak
white. The sync amplitude is very reliable because its always there at
300mV (OK, 286mV to be spot on). Continuously variable AGC would be a
little harder than range detecting but certainly doable. If you don't
have sync on the video, it will get more interesting. Personally, I
just fix the problem with the video since widely varying levels
implies faulty transmission lines/terminations which will muck it up
anyway. Fixing reflections from faulty cables automatically is
possible but way beyond simple opamps.
GG

Relevant Pages

  • Re: Automatic voltage scaling with op-amp?
    ... >be of any use in making a circuit that can automatically scale a 15khz ... >the net that shows how to use an op-amp as a peak detector. ...
    (sci.electronics.basics)
  • Automatic voltage scaling with op-amp?
    ... be of any use in making a circuit that can automatically scale a 15khz ... the net that shows how to use an op-amp as a peak detector. ...
    (sci.electronics.basics)
  • Re: Sony KV-20FV300
    ... and the video processing circuits. ... > In the Sony sets you are much better off with an "FV" series over the "FS" ... > Jerry G. GLG Technologies GLG ... > Velocity Modulation circuit. ...
    (sci.electronics.repair)
  • Re: black n white into white n black
    ... >inevert a white paper with black letters into a black paper with white ... >Camera circuit and modify it with a Class A amplifier i can be able to ... first you need to seperate the video syncs from the video picture ...
    (sci.electronics.design)
  • Re: FPGA NTSC signal with 2 resistors and PWM
    ... Video quality was not a requirement for this project (the ... but for color you have to add a sine and need to ... A digital video capture circuit is ... circuit I mentioned) was using Xilinx 16 bit shift register slices to ...
    (comp.arch.fpga)