CurtPalme.com Home Theater Forum

panzeroceania · Joined: 23 Sep 2011 Posts: 24 Location: Salem, Oregon

so far I understand that vertical refresh is how many times the display can draw a full screen in a second (correct me if I am wrong) so 60Hz vertical refresh, means the screen is refreshed 60 times in 1 second.

horizontal refresh, as I understand it, is your vertical resolution multiplied by your vertical refresh rate, so 640x480 at 60Hz would have a horizontal refresh of 480 x 60Hz = 28800Hz, or 28.8KHz, now of course this isn't exactly correct, as I understand it, there is some overhead, although I'm not sure how to calculate that.

My real question though, is what is CRT signal bandwidth, I've seen this referenced in MHz in instruction manuals. For example, the Sony G90 CRT projector has a textbook maximum vertical refresh of 150Hz, a textbook maximum horizontal refresh of 150KhHz, and a textbook max of 135MHz.

135MHz, that's a big number! so how does that relate to the horizontal refresh, vertical refresh, and resolution?

how does pixel clock relate to all of this?

and how does a CRT display know which aspect ratio to present an image in, or how many pixels horizontally an image should be?

any insight would be great!

hansilili · Joined: 09 Mar 2007 Posts: 302 Location: Köln, Germany

Hi,

this has been covered before, search for "bandwidth resolution frequency". Anyway

add horizontal and vertical porches to your screen resolution: Front-Porche (HFP/VFP), Sync-Width (HSW/VSW), Backporches (HBP/VBP), visible resolution (HRes/VRes).

Dot-Clock or Pixel-Clock o fthe signal is:
max resolution x (Framerate = FR)

(HFP+HSW+HBP+HRes) x (VFP+VSW+VBP+VRes) x FR

Pixel-Clock not the highes frequency of the usable signal, you need 2 pixels for a complete sine wave in perfect digital reolution So the viedo bandwidth is half the pixel clock. In analog systems you have more components limiting the bandwidth, eg cables, circuits.

This is about what you need:

redfox001 · Joined: 16 Mar 2009 Posts: 2257 Location: The Netherlands

Yes and to get 82 MHz flat video bandwidth you need like 5 times that bandwidth at -3db so 400 MHz and much more is better because the frequency response gets flatter.

Hulio · Joined: 15 Apr 2006 Posts: 494 Location: Belgium

To rule out some confusions about the relationship between frequency, resolution and pixelclock, here a doc. from the clever guys at Barco regarding this matter.
Maybe a sticky worth, Kal should decide...

CIR Engineering · Posted: Wed Jan 28, 2015 11:25 pm Post subject:

CIR Engineering · Posted: Wed Jan 28, 2015 11:36 pm Post subject:

redfox001 · Joined: 16 Mar 2009 Posts: 2257 Location: The Netherlands

This is also a good source to understand Bandwidth requirements versus Video resolution
http://www.maximintegrated.com/en/app-notes/index.mvp/id/750

The last post was about circuit bandwidth and slew rate requirements.

'Circuit-Bandwidth and Slew-Rate Requirements
The circuits that process video signals need to have more bandwidth than the actual bandwidth of the processed signal to minimize the degradation of the signal and the resulting loss in picture quality. The amount the circuit bandwidth needs to exceed the highest frequency in the signal is a function of the quality desired. To calculate this, we assume a single-pole response and use the following equation:
H(f)(dB) = 20log(1/(1+(BWS/BW-3dB)²).5)
Rearranging and solving for the -0.1dB and the -0.5dB attenuation points, we get the following:

BW-3dB min = BWS (-0.1db) × 6.55 EQ 3

BW-3dB-min = BWS(-0.5db) × 2.86 EQ 4
Where:
BW-3dB = the minimum -3db bandwidth required for the circuit'

So the conclusion is that you have two quality standards. The requirement to be only 0.1db down at the highest video frequency requires 6.55 times the minimum bandwidth. If it is allowed to be 0.5db down than only 2.86 times the minimum bandwidth is required. Another 1.5 times is added to allow for differences in components.

For UXGA (1600x1200) it means 701 MHz is required for -0.1db quality where 71.4 MHz is the minimum with -3db at the highest video frequency. That is almost 10 times. Shocked

See the article for the numbers.

stridsvognen · Guest

CIR Engineering · Posted: Fri Jan 30, 2015 2:01 am Post subject:

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

That was Chris Stevens baby. 22 pounds of Wet tantalums everywhere.

He told me about it too. Said it was so liquid an image it felt like it flow off the screen.

It originally was paired with the HD SDI AJA input card and a Tarannex Video Processor.

http://www.xymox1.com/Resume/Press/TPV104/tpv_jan_04_golden_eye.htm

And of the Reference imaging as well.

http://www.xymox1.com/Resume/Press/SGHTReview.pdf

Athanasios

stridsvognen · Guest