CurtPalme.com Home Theater Forum

[1031]

Guys. I dont have ready solution for you to tell what is best way to bypass that sd5401.
Nashou that bandwith thing on that chip dependts surrounding components-> output impedance of driverstage before it, sd5401 input capacitanse and "on resistance" of switch itself and capacitance of output. Those parameters combine circuit that is similar to r-c filter. Rc-filter pass low frequencies and cuts high frequencies. But i think bigger problem with that sd5401 chip is crosstalk between different signals. One solution could be that signal that goes to pins 11&14 are routed throught single swicht ( small fet) i remember that sony uses that kind of fet, i must look closer what was that fet and is that any better than sd5401.

[1031]

Ok it was 2sk160-k5. Somethig like that might work, i´m not sure but we must look closer...

[Nashou66]

I was looking at these. the first one is fast 4ns but only 200mhz, the second one is 450mhz but only 12 ns typical

http://focus.ti.com/lit/ds/symlink/ts5a3167.pdf

http://focus.ti.com/lit/ds/symlink/ts5a4596.pdf

here is another possibility not sure how to make it work though.

http://focus.ti.com/lit/ds/symlink/ts3v340.pdf

I will look for more, Jarmo I couldnt find that part you mentiond.

EDIT

ok this is the chip then, it is actually basicly one section of the SD5401 same company.
Still no bandwith specs though.

http://www.ortodoxism.ro/datasheets/linearsystems/SD211.pdf

Athanasios

[1031]

http://www.google.fi/search?hl=fi&q=High+speed+n-channel+dmos+switch&btnG=Google-haku&meta=

Yes that 2sk160 seems wery rare..or least Google didnt know it

[Nashou66]

http://www.ortodoxism.ro/datasheets/linearsystems/SD211.pdf

This seems to be one section of the SD5401 so we eliminate cross talk using it, but still no bandwidth specs.

Looks like the SD213DE (can type) or the SST213(surface mount) would be the best choice. At least we can eliminate the -107db of crosstalk in the SD5401 chip. do you think we should also bypass the DC restore section pins 8 and 10? There might be some cross talk getting into the dc restore signal on its way back to the input op amp, or would this just be overkill?





Athanasios

[9kids]

Something like this might work

http://www.pericom.com/pdf/applications/AB009.pdf
http://www.pericom.com/pdf/datasheets/PI5V330S.pdf

[Nashou66]

With the first one we would need to feed it both video signals , internal and external signal and have it be able to:
1) switch on internal video and external video switched on to overlay the internal video
2) switch on external video and switch off internal video for normal viewing
3) switch off external video and switch on internal for internal video patterns only.

trying to figure out what signals to send as the trigers for each situation seems complicated to me.

And i have looked over the schematics and read the service manual and I can not find any chip that does the overlay of video. The SD5401 does not do that as far as i can tell, there are four seperat outputs one for each channel , no combining of signals is done in that chip. It looks fron the schematics that internal and external video is just sent simultaniously from this point on this section of the schematics labled red , to the AD834 on another page of the schematics where from there it goes to the rgb ouput op amp. I think Contrast is addded inside the AD834 but dont quote me on this. Two signals are then sent to CLC449 op am to the inverting and non inverting pins then from there to the rca jacks.


I think just seperating one section of the SD5401 with the SD213 is the simplist way to eliminate crosstalk which seems to be the only weak link with that original chip. it does state it is a high frequency chip so i think the bandwidth is not an issue since i dont even think MP bypasses that chip on his mods. And they do 1080p easily.

Athanasios[/img]

[9kids]

[Nashou66]

I was just thinking this and was going to add to my post! I was going to say " I just realized that the SD5401 has really fast switching so it might be switching very fast between internal and external thus showing the menu on the screen" But I didnt understand the part you explained about knowing where in the video field to turn on and off, this is done by the CLM right? It sends pulses telling the ex-video to turn off and at that same precise moment tells the internal side of the switch to turn on. Thanks for also clarifying this for me, now I understand,and also why the relay wont work unless it is split and when we want to see the menu we switch to the way the projector works now, and if we want to watch video only we could bypass the sd5401.But that seems lik to much work. So looks like the SD213 or SST213 is our best choice to eliminate the cross talk .I also talked to a tech today from Linear and he told me that noise is negligable on the chip but he is not sure of the bandwidth but is sure it is more than enough for high resolutions.

Thanks 9Kids...whats your name anyhow if you dont mind me asking.

Athansios

[Nashou66]

Well I went ahead and requested some free samples of both the SD213 and the SST213. its basicly a single version of the SD5401 But we loose the crosstalk between the internal switches I am just wondering if we should also remove the clamp section from the SD5401 and use another SD213 for that?

Athanasios

[9kids]

[Nashou66]

John you explained it like a great professor i once had in college. Once i get the chips in i'll give it a shot ,one on the video path and then i'll also try one on the clamp path that goes to the dc restore. Not sure if the cross talk is that bad an issue but id be neet to see if something like this works, then maybe we can find some other chip where we know the specs are correct...but then again most specs are not really made with the conditions of real world use.

Athanasios