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THE MOD
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Wed Jan 11, 2017 3:40 pm    Post subject: Reply with quote


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I’ve made the coarse schematic diagram of the VNB-DB AD834 concept for the curious eyes.
The basic structure is a simple combination of the XG-VNB and the VNB-DB design, except for the box signed as tricky part, well that is the tricky part…
In normal operation (ie. video is projected from the input) Q4 and Q5’s base terminals are tied together to +5V through R51, so they operate in a so called common base configuration, this is 1:1 how the original 03P VIM also works, the OSD signal can’t make through the output because it is detached by U7 switch, even if there is some crosstalk that causes a so called common mode noise which is further rejected by the output opamp. On the other hand If the OSD input is selected the AD834 gets muted, then Q4 and Q5 common base connection is splitted up and U7 switches U9-A output to Q4’s base, in the meantime the voltage there is also lowered to +2.5V so we don’t run out of dynamic range. U9-A is a non inverting summing amplifier which basically shifts the OSD input signal to +2.5V. Now if there is nothing on the OSD input both Q4 and Q5 base sees the same voltage, the circuit is in balance (= zero output). If there is some voltage on the OSD terminal that imbalances Q4 and basically drives the output opamp so the OSD can be seen...



VNB_DB_concept.pdf
 Description:
VNB-DB AD834 concept

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 Filename:  VNB_DB_concept.pdf
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Wed Jan 11, 2017 10:03 pm    Post subject: Reply with quote

I have the investor for this project, so it will most likely come alive. Thumbs Up
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
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The MOD: VNB-DB
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mp20748



Joined: 12 Sep 2006
Posts: 5358
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Thu Jan 12, 2017 1:15 am    Post subject: Reply with quote

gjaky wrote:
I’ve made the coarse schematic diagram of the VNB-DB AD834 concept for the curious eyes.
The basic structure is a simple combination of the XG-VNB and the VNB-DB design, except for the box signed as tricky part, well that is the tricky part…
In normal operation (ie. video is projected from the input) Q4 and Q5’s base terminals are tied together to +5V through R51, so they operate in a so called common base configuration, this is 1:1 how the original 03P VIM also works, the OSD signal can’t make through the output because it is detached by U7 switch, even if there is some crosstalk that causes a so called common mode noise which is further rejected by the output opamp. On the other hand If the OSD input is selected the AD834 gets muted, then Q4 and Q5 common base connection is splitted up and U7 switches U9-A output to Q4’s base, in the meantime the voltage there is also lowered to +2.5V so we don’t run out of dynamic range. U9-A is a non inverting summing amplifier which basically shifts the OSD input signal to +2.5V. Now if there is nothing on the OSD input both Q4 and Q5 base sees the same voltage, the circuit is in balance (= zero output). If there is some voltage on the OSD terminal that imbalances Q4 and basically drives the output opamp so the OSD can be seen...


Great job here..Thumbs Up

Amazing work done to multitask the various components for seamless video output.
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Thu Jan 12, 2017 7:02 am    Post subject: Reply with quote

mp20748 wrote:

Great job here..Thumbs Up

Amazing work done to multitask the various components for seamless video output.


I think I just say thanks! Smile

Anyway, I felt that the above mentioned design is a bit overengineered, sometimes you have to do the wrong thing to find the right one, so later the day I found out there is a much simplier solution to add the +Z input, namely: leave the common base stage untouched, R46 resistor on the above posted diagram is a 301R resistor tied to ground, now if that resistor is tied to the OSD output instead of ground there we have the +Z input, it is that simple...

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
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mp20748



Joined: 12 Sep 2006
Posts: 5358
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Thu Jan 12, 2017 9:50 am    Post subject: Reply with quote

Your design concept looks more like what I've seen on the Sony Beta decks of past, and what you'll see on a IC block diagrams. Complex for sure, but makes sense. I'm confused on the two inputs (X/Y) for U5 and where the "gamma" input (R62) goes.

It's also genius how you're getting the OSD/Test in the chain at Q4 and not create a bandwidth issue, and at the same time disrupt (break into) both Q4 and Q5 and not affect their finicky operation, mainly because during source video the base of both are not a part of the critical bandwidth path (C29 and R51). You sneak the OSD/TestP into that very sensitive network and do so without compromising the high bandwidth video. Or that's how it appears from my perspective.


Yes, great job at using low bandwidth switches to control high bandwidth signals, and do so with no bandwidth compromise.

Great work on using the matrix of the AD834 input for both Source and Gamma, because putting anything on the "feedback/ground" connection of an op-amp is not good for high bandwidth op-amps.


Also good that you kept both R32 and R50 at that value, because the AD834 would definitely need to be decoupled from the other stages. And you have to make sure a regulator is supplying the +9 supply



Edit: I read your last post, and I agree and was thinking very similar to put OSD/Testp somewhere else, on or after U6. And an even better idea to have not put it on the feedback/ground lead of U6


.
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Thu Jan 12, 2017 11:15 am    Post subject: Reply with quote

The gamma is what gave me the most headache so far. As I saw from calibration curves is that the blue drops the high end with linear drive. So I aimed adding more gain dynamically based on the input signal. The first version was a simple comparator so under the threshold leve the gain was A over the threshold the gain was B, but as turned out this is not really what was needed, the second trial was to linearize the comparator so it would give a proportional output to the input signal (the higher the input the more it „push”), this was far better but then it turned out that at high frequencies like 1080P 72Hz the comparator introduce quite some lag in the signal, so the input signal was at it s peak with a single pixel, but the gamma generator output was lagged by several nanoseconds, so it was actually modulated the gain in the wrong way, with slower signals it tracked fine. There were other problems though. The correction waveform and the contrast singnal was summed at an emitter folower’s base, being that way the summing was carired out by changing the ratio of the resistors on the base, this was double bad on one hand the resistance needed to be as low as possible, but still needed to be around 1k from the corrector circuit, the other bad was the gamma rate was seriously interacted with the actual contrast setting. You set the gamma rate and your contrast went away as well and vice versa.

To overcome these problems active summation was made thereafter, knowing the input of the multiplier is X=(X1-X2). Unfortunately the contrast and the gamma signal have to be added not subtracted. Fortunately the multiplier knows elementary math well: Gamma-(-Contrast)=Gamma+Contrast. Obviously I chosed to invert the contrast signal which is a quasi DC signal anyway, rather than the precious gamma signal. With the newest solution the gamma curve is derived by a simple voltage divider from the input signal (no lag), since the impedace was kept at quite low level we don’t have to care about frequency response either (I tested a 200 Ohm SMD trimmer before that did not affect the bandwidth at any setting in an 50 Ohm terminated system even without added peaking) and here the resistance even smaller by an order. This way gamma and contrast signals are not interacting.

After all it turned out this gamma concept is essentially the same as what was made in the Barco 909 -which I did not understand for a long time how/why is it working… It is a popular trick to disable the gamma on those barco boards but there the input derived signal was switched by conventional multiplexers, with only 4 fixed settings and even the resistance wasn’t kept at a very low levels so they had to peak those dividers, also in the barco the gamma is made in a separate AD835, that made a difference in signal chain integrity between green and the other colours as well. I admit this later gamma solution is not tested in reality yet, but the new PCBs are already under manufacturing, and I expect to have them in two weeks or so. Worst case the gamma feature can be disabled, not many projectors have usable gamma feature if any at all…

Here is the simplified version of the AD834+Z circuit, it is by far more simple than the previous idea, although here the switch is involved into the signal path to some extent as R7 and R8 should be kept in balance at any circumstances.



AD834+Z_simple.JPG
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 Viewed:  9241 Time(s)

AD834+Z_simple.JPG



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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mp20748



Joined: 12 Sep 2006
Posts: 5358
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Thu Jan 12, 2017 12:53 pm    Post subject: Reply with quote

gjaky wrote:
After all it turned out this gamma concept is essentially the same as what was made in the Barco 909 -which I did not understand for a long time how/why is it working… It is a popular trick to disable the gamma on those barco boards but there the input derived signal was switched by conventional multiplexers, with only 4 fixed settings and even the resistance wasn’t kept at a very low levels so they had to peak those dividers


It was a good idea to do it that way, and I'm with you in that I never could figure out how it worked either. Limited with only four settings, but the bigger problem was here as you also indicated:

Quote:
also in the barco the gamma is made in a separate AD835, that made a difference in signal chain integrity between green and the other colours as well


On your design you seem to have gotten around this and when I was modifying that same board I removed those gamma stages.

And with your design not having or adding another circuit in the chain, it's a win all the way around. Especially knowing how difficult it is to keep 1920X1080P intact and as true to the source as possible.


Quote:
I admit this later gamma solution is not tested in reality yet, but the new PCBs are already under manufacturing, and I expect to have them in two weeks or so. Worst case the gamma feature can be disabled, not many projectors have usable gamma feature if any at all…


Hey, that's what its all about, and why it takes so long to get these stages right. Turning theory into reality is the challenge. And so far, you're on a roll. I remember well, the many PCB designs I got in the mail and at the end of the day, I was back designing another.


Quote:
Here is the simplified version of the AD834+Z circuit, it is by far more simple than the previous idea, although here the switch is involved into the signal path to some extent as R7 and R8 should be kept in balance at any circumstances.


Yes.
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Wed Jan 18, 2017 6:05 pm    Post subject: Reply with quote

So the postman came...


VNB_DB_new.jpg
 Description:
Blank VNB-DB Boards
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VNB_DB_new.jpg



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB


Last edited by gjaky on Fri Jul 06, 2018 7:11 pm; edited 2 times in total
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 25418
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Wed Jan 18, 2017 6:44 pm    Post subject: Reply with quote

gjaky wrote:
So the postman came...



Did he ring twice? Laughing

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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Wed Jan 18, 2017 7:09 pm    Post subject: Reply with quote

AnalogRocks wrote:

Did he ring twice? Laughing


I don't know, my wife took over the package... Very Happy

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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Curt Palme
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PostLink    Posted: Wed Jan 18, 2017 7:16 pm    Post subject: Reply with quote

Awesome work!
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Fri Jan 20, 2017 4:11 pm    Post subject: Reply with quote

I put together the AD834 circuit like above (AD834+Z_simple.JPG) on a blank XG-VNB PCB, it seems the simple idea works quite well, the switch does not seem to interfere with the input signal.
We measured the bandwidth of the circuit at work on a 9GHz Vector Network Analyzer as well. The circuit was tuned relatively convervatively for bandwidth, it uses 2SA1765 PNP transistors and CLC449 opamp. the output shown below was recorded at 2V amplitude. As can be seen, it remains within 1dB up until 250MHz, then falls a bit, but leaves the -3dB point finally slightly over 500MHz...



834_-3dB.png
 Description:
AD834 VNB-DB concept with simple +Z solution.
 Filesize:  12.56 KB
 Viewed:  9032 Time(s)

834_-3dB.png



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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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thewolfman



Joined: 28 Mar 2011
Posts: 1304
Location: Sweden


PostLink    Posted: Fri Jan 20, 2017 10:24 pm    Post subject: Reply with quote

I'm not technicality good at all but wonder how your got AD834 into the mix without a vim 03 at all.. you don't need a vim at all?

You and MP should work together and find a solution to what the next step should be.
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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Fri Jan 20, 2017 11:02 pm    Post subject: Reply with quote

thewolfman wrote:
I'm not technicality good at all but wonder how your got AD834 into the mix without a vim 03 at all.. you don't need a vim at all?

You and MP should work together and find a solution to what the next step should be.


the new 03P VIM uses DIP-8 (through hole) AD834s, my design uses SOIC-8 AD834 (SMD), so actually having a new 03p VIM help little in constructing a daughterboard. Otherwise, both the AD835 and AD834 are readily available from electronic parts suppliers, like DigiKey, Farnell etc. They are not cheap though: an AD834 is 35 USD/piece.
This is why the price of the AD834 mod would be higher...
-I sell the VNB-DB (AD835) for 300USD including every needed modifications and extra cables to the VIM, LVPS, and HDM, but for that cost the customer must supply the 02p VIM to modify, if the customer wants he can send the VNB as well and I perform some simple modifications for those as well for no extra charge.
-There is a budgetary option for hard core tinkerers. For 50 USD the customer can get a set of blank PCBs (1 for the VIM, 3 for the VNBs), the needed cables and connector, a part list, and instructions how to perform the modifications. The customer sources all parts for himself.
-The AD834 version, let's call it as ULTIMATE VNB-DB. So, if that indeed works out then that would cost 500USD, with the same conditions as above, with the addition that the ULTIMATE VNB-DB could offer the benefit to jump through the preamp IC on the VNB, so for that the VNBs are also needed to be sent in for modifications. I plan this to be a special small product run with only 3 sets available (+ I keep one for myself, and 1 is reserved to the original funder of the project) with gold plated PCB, premium MCX video connectors etc.

MP and I walk on different ways, and that's how it should be IMO.

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
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gjaky



Joined: 05 Jun 2010
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PostLink    Posted: Tue Jan 31, 2017 8:50 pm    Post subject: Reply with quote

I decided to post some information on stock VIM boards I have here.
The goal here is to demonstrate their bandwidth that actually reach the VNB.
About the measurement rig: The source is my trusty old Asus GeForce 6600GT videocard in an appropriate computer, The card was set to output 1080P 72Hz, the test signal is a multiburst signal with 4, 3, 2, 1 on:off pixel sequence on gray background.
First the output of the videocard was measured after 3m of conventional d-sub to RGBHV cable, fisrst I tested how this signal looks on my oscilloscope:


You can see some roll off towards the right side of the scope screen, ideally all "box" should be equal in amplitude. Nevertheless the roll of as calculated is about -0.3dB between 1:1 and 4:4 pixel pattern, this implies the imperfections of the DAC output of the videocard, my oscilloscope's finite bandwidth and the cable's attenuation, it is what it is.

This signal was then fed to a bone stock 02p VIM from 1998, the contrast was set to maximum (but I did not care to max out the drive under white balance settings). The output of the signal was observed on oscilloscope with using the original ~60cm mini RCA cable (which is a Belden RG-179 coax on my machine) as interconnect, so this is the actual signal that would normally reach the VNB in stock conditions:


Here as you can see the output at 1:1 is rolls off quite much, down to about the half of the amplitude than the other boxes, this corresponds closely to -6dB roll off, this of course includes the imperfection of the input signal too. There is some peaking at 2:2 (not seen at input!) as it has higher amplitude than the 4 and 3 pixel wide sequences. But generally the uniformity of the boxes are similar to the input signal.

Just for fun I tested an old (1994) M9000 03p VIM that uses AD834 analog multipliers and HFA1100 opamps.



Here the bandwidth is not better not even by a tiny bit. What it is worth noting that there are bands inside the "boxes" those were not seen at the input, those mean reflexions/disturbances in the output signal generated by the VIM itself, I checked the signals in more detail and the pulses have a really ugly shape, this board produces very high distortion!

Tomorrow I want to perform this same test on my VNB-DB board's output.

Stay tuned! Wink



OLD_VIM_03p.jpg
 Description:
M9000 03p (AD834) VIM Video out
 Filesize:  135.08 KB
 Viewed:  4157 Time(s)

OLD_VIM_03p.jpg



VIM_02p.jpg
 Description:
VIM 02p video out
 Filesize:  141 KB
 Viewed:  4157 Time(s)

VIM_02p.jpg



GF6600GT_1080P-72Hz_out_at_cable_end.jpg
 Description:
GeForce 6600GT VGA output signal on oscilloscope. The reference signal.
 Filesize:  175.49 KB
 Viewed:  4157 Time(s)

GF6600GT_1080P-72Hz_out_at_cable_end.jpg



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB


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Curt Palme
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PostLink    Posted: Tue Jan 31, 2017 11:36 pm    Post subject: Reply with quote

Excellent work! Now I'm excited to see scope waveforms! Well done! Very Happy
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ronaldus



Joined: 25 Dec 2010
Posts: 173
Location: france


PostLink    Posted: Wed Feb 01, 2017 7:38 am    Post subject: Reply with quote

Hi Gabor,

This is how we can compare different systems!

Would you mind sharing this test pattern with me?

I'll do then the same with my system to see how it looks.

regards,

Ron.
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barclay66



Joined: 27 Jun 2011
Posts: 1250
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TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Wed Feb 01, 2017 8:26 am    Post subject: Reply with quote

Hi,

This should be the corresponding file...

Regards,
barclay66



Multiburst.png
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Multiburst.png


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gjaky



Joined: 05 Jun 2010
Posts: 2626
Location: Budapest, Hungary


PostLink    Posted: Wed Feb 01, 2017 4:50 pm    Post subject: Reply with quote

So I finished the first VNB-DB on the newest PCB.
The first good news is that the gamma correction is now working as it was intended -without affecting the bandwidth.

But lets look at the bandwidth of the VNB-DB as it was promised.

The settings are the same as yesterday (1080P 72Hz), here also there is obviously some roll off, but after doing the math this gives -1dB roll off only (of which -0.3dB is directly can be addressed to the input signal). I want to note here that the rule of thumb definition for the decibel scale is that 1dB difference is the smallest change in the signal what an observer can detect.



VNB-DB_out.jpg
 Description:
Output of the VNB-DB (AD835)
 Filesize:  145.62 KB
 Viewed:  4156 Time(s)

VNB-DB_out.jpg



_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB


Last edited by gjaky on Fri Jul 06, 2018 7:09 pm; edited 2 times in total
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mp20748



Joined: 12 Sep 2006
Posts: 5358
Location: Maryland

TV/Projector: 9500LC Ultra / Super 02 and 03 VIM


PostLink    Posted: Wed Feb 01, 2017 5:02 pm    Post subject: Reply with quote

That's not roll-off, that's normal when using a Multiburst pattern @ 1080P.


When doing multiburst at that bandwidth, its best to go dual probe/display (before/after). Showing them both at the same time one above the other.
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