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(non professional) VGA card bandwidth evaluation
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 27, 2013 3:31 pm    Post subject: (non professional) VGA card bandwidth evaluation Reply with quote


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Here we are, I started a small campaign to evluate the common VGA card's output performance, there are a lot of parameters that should be considered, but for now I focus only on the rise time measurement giving a clue about the bandwidth of the actual card, if there is interest in this thread the measured parameters could be extended later of course.

The measuring theory and method
This is not a reference level measurement, but later when the number of the measured cards are growing they could give a good basis of comparision.
The best way would be to get an oscilloscope with bandwith of at least 500MHz, but that's not a cheap toy for fun experiments. So I choose the indirect way of measurement.
I have an old HP 1720A analog oscilloscope, originally it was a military item, used by the USAF, after that it still remained in the corporate sector until I bought it from a friend who bought it at their rollout. It has an advertised bandwidth of 275Mhz, has switchable 50 Ohm input, it was held in good hands, but the last calibration date is unknown, otherwise it seems to be accurate enough for hobby purposes.
The VGA cards are connected directly to the scope's BNC input with a 3m (10 feet) long, VGA-BNC cable Fujikura brand. Though the standard VGA output would require a 75 Ohm termination I used the scope's 50 Ohm internal termination, but that does not affecting the rise time of the circuit. I did this to measure with the least intervention to the original signal and to ease the measurement.
A system's bandwith is proportional to its rise time and vice versa, the used method is based on the theory of rise time of cascaded blocks, in a perfect world this would mean if I would connect an infinitely fast rising edged signal to my oscilloscope I would measure 1,27ns rise time (=0,35/275MHz, see above the wiki link).
An other example: If I connect a (flat to) 400MHz (->tr=0,87ns) VGA card to my (ideal) scope (->tr=1,27ns) that would mean an 1,54ns overall rise time, and this is actually observable on my oscilloscope since it has a 1ns/div speed, that is further divided to 5 subdivisions.

For the further calculations I difine that my scope's rise time is 1,3ns, wether it is really or not, but until the measuring rig remain the same all myl measurements will be comparable.

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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 27, 2013 3:44 pm    Post subject: Reply with quote

Asus nVidia GeForce 7950GT 512MB (PCIe):
Measured in 800x600 with a specially breed test pattern (to ease scope triggering) otherwise this is a simple multiburst, bandwidth pattern.
There was a slight overshoot, I set the 100% level to where the signal settled,
Total measured rise time(10%-90%): slightly less than 1,6ns
solving the equation gives us: 0,93ns calculated rise time for this card which would mean a bandwidth of about 375MHz, where the advertised bandwidth is 400MHz.



GF7950.jpg
 Description:
nVidia GeForce 7950GT rise time on a HP1720A o'scope
 Filesize:  39.74 KB
 Viewed:  22932 Time(s)

GF7950.jpg



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Last edited by gjaky on Wed Dec 04, 2013 12:31 pm; edited 1 time in total
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 27, 2013 3:54 pm    Post subject: Reply with quote

integrated intel GMA950 (i945GZ on a foxconn motherboard):
Measured in 1920x1080 96Hz with the same pattern as above
Total measured rise time: 2,4ns
Calculated rise time for this VGA: 1,77ns -> ~200MHz, this is about the half of the advertised 400MHz.

That's it for now, an ATI HD3650, and other nVidia cards will follow soon.



GMA950.jpg
 Description:
intel GMA950 integrated VGA rise time on a HP1720A o'scope
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GMA950.jpg



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Last edited by gjaky on Wed Dec 04, 2013 12:31 pm; edited 1 time in total
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 26690
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Wed Nov 27, 2013 5:26 pm    Post subject: Reply with quote

I'll be interested to see the ATi 3650, I think that's what is in my HTPC
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fragzero




Joined: 30 Aug 2012
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PostLink    Posted: Wed Nov 27, 2013 5:34 pm    Post subject: Reply with quote

It might be a good idea to photograph the card, not every manufacturer uses the reference design!
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 27, 2013 5:56 pm    Post subject: Reply with quote

fragzero wrote:
It might be a good idea to photograph the card, not every manufacturer uses the reference design!

Of course that can be done, the above mentioned asus card is a reference design, asus didn't even bothered to remove the original nvidia sticker from the heatsink, they just put their sticker on it Razz
In the meantime I figured out maybe I can test a HDF1 soon too..

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winny




Joined: 09 Oct 2013
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Location: Sweden

TV/Projector: BD808s, BG1209/2


PostLink    Posted: Wed Nov 27, 2013 8:22 pm    Post subject: Re: (non professional) VGA card bandwidth evaluation Reply with quote

gjaky wrote:
The best way would be to get an oscilloscope with bandwith of at least 500MHz


I have a 500 MHz DPO4000 at work and if you send me the test pattern, I'll gladly measure whatever card I have laying around for you. Someone with a GHz scope should be better though.
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Nov 27, 2013 9:23 pm    Post subject: Re: (non professional) VGA card bandwidth evaluation Reply with quote

winny wrote:
gjaky wrote:
The best way would be to get an oscilloscope with bandwith of at least 500MHz


I have a 500 MHz DPO4000 at work and if you send me the test pattern, I'll gladly measure whatever card I have laying around for you. Someone with a GHz scope should be better though.


Sure! See the attached picture bellow, I used this at full screen in 800x600, that's about enough as we are only interested in the steepness of the rising edge.



burst2.GIF
 Description:
pattern
 Filesize:  11.59 KB
 Viewed:  22883 Time(s)

burst2.GIF



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gjaky




Joined: 05 Jun 2010
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Location: Budapest, Hungary


PostLink    Posted: Wed Dec 04, 2013 12:29 pm    Post subject: Reply with quote

Reference (Sapphire) ATI Radeon HD4650 (PCIe):
Measured at 640x480
Measured rise time: 1,8ns
Calculated rise time for VGA: 1,2ns -> ~280MHz (claimed bw: 400MHz)



ATI_HD4650.jpg
 Description:
 Filesize:  35.45 KB
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ATI_HD4650.jpg



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fragzero




Joined: 30 Aug 2012
Posts: 344



PostLink    Posted: Wed Dec 04, 2013 1:54 pm    Post subject: Reply with quote

Any chance you can test a HD6350 reference design?

Quote:
http://tiptop.lt/blog/wp-content/uploads/2010/09/amd_radeon_hd_6350.jpg


Very popular HTPC card last generation!
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Wed Dec 04, 2013 2:25 pm    Post subject: Reply with quote

fragzero wrote:
Any chance you can test a HD6350 reference design?

Quote:
http://tiptop.lt/blog/wp-content/uploads/2010/09/amd_radeon_hd_6350.jpg


Very popular HTPC card last generation!


Unfortunately, I don't have a source to borrow that card, yet.
But I have an nvidia GF6600 and GF8800 card on my list, so we'll see at least how are the generations realated to one another with the nvidia cards... Otherwise I doubt the manufacturers took much effort to make the DACs even better and better with the ongoing generations, it's like wasted wasted time for the mass market... It would be also interesting if a very recent card has any cuttings in the analog performance compared to older cards?

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gjaky




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PostLink    Posted: Fri Dec 13, 2013 10:01 pm    Post subject: Reply with quote

ASUS GeForce 8800GTS 320Mb (G80 core, PCIe):
Measured at 800x600
Measured rise time: ~1,7ns
Calculated rise time for VGA: 1,1ns -> ~320MHz (claimed bw: 400MHz) But note the output is very similar to the GF7950GT's only with less overshoot, thus the slightly worse rise time.



GF8800GTS.jpg
 Description:
 Filesize:  47.42 KB
 Viewed:  22721 Time(s)

GF8800GTS.jpg



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CasetheCorvetteman




Joined: 09 Nov 2008
Posts: 6319
Location: Australia


PostLink    Posted: Sat Dec 14, 2013 2:18 am    Post subject: Reply with quote

What do you get from a GigaByte 760 GTX OC Edition?
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gjaky




Joined: 05 Jun 2010
Posts: 2789
Location: Budapest, Hungary


PostLink    Posted: Sat Dec 14, 2013 10:00 am    Post subject: Reply with quote

CasetheCorvetteman wrote:
What do you get from a GigaByte 760 GTX OC Edition?

Nothing, yet... Razz

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CasetheCorvetteman




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PostLink    Posted: Sat Dec 14, 2013 10:56 am    Post subject: Reply with quote

Thats what i have in my main rig, 650Ti in the other.

Both allow me to select Generic CRT for 3D even over HDMI.

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gjaky




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PostLink    Posted: Sat Dec 14, 2013 12:43 pm    Post subject: Reply with quote

The "latest" nVidia card that I can borrow is a GT240, which is pretty old as well Smile
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CasetheCorvetteman




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PostLink    Posted: Sat Dec 14, 2013 2:28 pm    Post subject: Reply with quote

Yeah thats WAY down the order from what i have here...
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noos@xp37+




Joined: 17 Jun 2008
Posts: 464
Location: Berlin/Munich


PostLink    Posted: Sat Dec 14, 2013 6:01 pm    Post subject: Reply with quote

I use a 280gtx, and I have one for SLI/spare lying around here. With the next parcel to HU I will include it for you. Great work Gabor!
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CasetheCorvetteman




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PostLink    Posted: Sun Dec 15, 2013 12:01 pm    Post subject: Reply with quote

I have the HDMI output connected to the AVR for audio, the RGB to the projector, then the DVI goes to my 27" monitor.
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gjaky




Joined: 05 Jun 2010
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PostLink    Posted: Sun Feb 21, 2016 7:20 pm    Post subject: Reply with quote

A new approach, multiburst signal.
Just because I was at it...
nVidia Geforce 6600GT



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1080p 72Hz
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1080P 60Hz
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