Samsung 900NF maximum refresh rate?

[Biggs]

If you look here, there's a guy running his 900NF @ 1600 x 1200 at 93 MHz refresh rate. Would this damage the monitor if used for extended periods of time?

Also, according to this,




There is a relatively simple way to calculate the maximum refresh rate of a monitor (simple for me, I've been doing this for 15 years). You need to know the following. The maximum horizontal scan frequency, and the resolution that you want to run. All manufacturers publish this data. The formula below will give you an approximate refresh rate, to calculate the exact refresh rate the math gets harder and you need to know more details about the monitor such as the exact horizontal and vertical blanking time.

(1 / Horiz Scan Freq) * (Number of Vertical lines + 50) = x (1 / x) = Refresh rate

So in the case of a 121Khz monitor it has a (121,000) 121Khz horizontal maximum scan rate. Lets assume that you want to run 1600 x 1200 resolution. What is the theoretical maximum refresh rate?

(1 / 121000) = .000008264 * (1200 + 50) =1250 Note: Add 50 lines to the total number of line to account for vertical blanking time.

0.000008264 * 1250 = 0..010330579

1 / 0..010330579 = 96.8Hz maximum vertical refresh rate (Convert back to time base)

As long as the horizontal and vertical refresh rates are within the range of the monitor the monitor will display an image.

All this math leads to the following.

There are classes of monitors based on the horizontal scan frequency. Typically as the HSF goes up so does the price of the monitor.

I'm amazed at how many people purchase monitors that are overkill for the resolution or application they want to run. If you need to run 1856 x 1392 or even 2048 x 1536 spend the bucks and buy a high-end monitor. If you are going to run 1280 x 1024 up to 1600 x 1200 on a 21" monitor you can save $$$ by purchasing a monitor that is optimized for those resolutions. Most games for example run at lower resolutions. There is little benefit in purchasing a monitor with higher resolution capabilities than the one you plan to use.

The horizontal scan frequency is the key specification to look at. 70 - 85Khz monitor is optimized for 1024 x 768 at 85Hz
92 - 96Khz class is optimized for 1280 x 1024 at 85Hz
107 - 110Khz monitor is optimized for 1600 x 1200 at 85Hz
115 - 117Khz Monitor is optimized for 1856 x 1392 at 85Hz
121Khz is optimized for 1900 x 1200 Cinema screen




the maximum refresh rate usable @ 1600 x 1200 would be 88Mhz. What are your thoughts?

 

[Gosharkss]

Biggs

Thanks for re-posting my formula. The math says the 900NF is a 110Khz monitor and that 88Hz at 1600 x 1200 is the maximum refresh rate. You can reduce the horizontal blanking time in order to achieve faster refresh rates. So in my formula use a smaller number than the 50 I use for blanking time.

The drawback to reducing blanking time is the deflection yoke does not have enough time to settle after drawing a horizontal line. Wrapping of the screen image around the sides may occur. Also you may see a dark bank down the left side of the monitor. Excessive yoke heating may occur and the expected life of the monitor may decrease.

In fact I'm surprised the monitor did not loose horizontal sync altogether. Usually if you run a monitor out of spec it will not recognize the signal and put itself into energy save mode.

Also there is a typo, no monitor can run 1600 x 1200 at 93Mhz, Mega-Hertz, I don't think so. They mean Hertz, not millions of Hertz.

What I have found in many talks with customers is that they really do not know what resolution they are running or how to figure it out. In the case that you post, I would bet the user was really running 1280 x 1024, just a guess but based on my years of experience this is almost always the case.

Jim

 

[Biggs]

Thanks for info. I'm just curious though, how did you come up with that formula?

 

[Gosharkss]

Biggs

If you have not already figured it out, I'm the Chief hardware engineer at Cornerstone / Monitorsdirect.com. It is my job to know these formulas in order to design and specify my monitors.

The formula is based on VESA industry standards and is similar to the one at the following site.

http://www.hut.fi/Misc/Electronics/faq/vga2rgb/calc.html

I have a detailed formula for figuring out video card timing but it is much more complicated and requires details about the monitor that most manufacturers do not publish like the pixel clock, front porch, back porch, blanking times etc.

VESA has published a formula called GTF or (Generalized Timing Format). Most video card and monitor companies use this formula to make certain the video signal from the card matches the requirements of the monitor.

I use my simple formula as a guideline to show people that monitors come in classes, like I explained in the formula that you re-posted. It is not intended to be 100% accurate but gives a general idea of the math behind the video signal interface that all video card and monitor designers need to know.

I see many people in this forum recommend monitors and other equipment without giving any details as to why they think their choice is the best. I try to take it one step further and explain the details behind my opinions.

Good luck

 

[Biggs]

Mucho thankso man, you're brilliant analysis has helped me decide which monitor to get!

 

[Gosharkss]

Glad to help out.

 

[Biggs]

One more thing Jim, I need your opinion(s) regarding using BNC cables at high resolutions. Is there really an improvement? Is the BNC cable something like a cable which has the 5 outputs on one end and a D-Sub 15 output on the other? I've heard that this type will defeat the purpose of BNC because the signal will still pass through the D-Sub 15 connection to the video card. So what are your thoughts?

 

[Gosharkss]

I think you read one of my other posts regarding BNC connectors. You can look back in the treads from a few weeks ago and find my posts.

I do not believe BNC connectors on one end of the cable helps all that much. If the cable had BNC on both ends then, I'm certain they would help, especially at higher frequencies. Some people claim they make an improvement in the video quality, really all they do is reduce the possibility of refections from that end of the cable. The cable itself 75 ohm coax is the same cable used in most 15-pin to 15-pin cables the manufacturers provide with the monitor. Some manufacturers may still use twisted pair cable, I would avoid twisted pair cable for video at all cost. Call the manufacturer and make certain they are using coax in the video cable.

This will also give you a good idea of the service you will receive from that manufacturer should you need them after the purchase.


Good Luck