What should be the minimum Oscilloscope characteristics for DVB-ASI examination? - Page 1
Forum section: electronics / beginners

author: swartkatt
author_rank: Contributor
timestamp: February 27, 2015, 08:52:55 pm
content: Dear Dave aficionado'sI have a very few understanding of electronics and about oscilloscopes. I am an Arduino person and i start to play with electronics not a long time ago. The best way to learn something is to start with a hard project to achieve - is my way to learn things. I want to analyse and i want to process DVB-ASI streams. There has a good opportunity came up in my region to buy an Oscilloscope with a reasonable price.Therefore i do not have enough time to dig around and make a research for an answer of my own question. Key Features of the oscilloscope which i would like to buy is listed below. My question is if i can examine a full DVB-ASI stream with this oscilloscope? If it is not capable; what should be the minimum Oscilloscope characteristics for DVB-ASI examination?"DVB-ASI is carried at a 270 Mbps line rate. The 270 Mbps bit-rate on the link is derived from a 27 MHz byte clock multiplied by 10 bits. The carrier frequency of a DVB/ASI signal is 270 MHz. The maximum effective bit rate is 214 Mbit/s."I just can not make a calculation and a meaningful conclusion from the information above - what kind of an equipment is sufficient to visualize this stream. How much bandwidth do i need, which sampling rate is enough, how much sampling memory is sufficient etc.I just presume that 500MHz bandwidth should be the minimum bandwidth because of the 270 MHz carrier frequency, and presume that 1GS/s Sample Rate should be enough because of the 214 Mbit/s payload and i do not have any ideas how much do "Recording Length of 50,000 points memory" play a role in my scenario?All of my assumptions might be incorrect because i am a beginner and i need guidance!Key Features of the oscilloscope which i would like to buy is listed below.TEKTRONIX TDS 540A 500MHz Digital OscilloscopeKey Features:----------------------------------500 MHz Bandwidth1 GS/s Sample Rate4 Input ChannelsRecord Length to 50,000 points8-Bit Vertical ResolutionThanks for your time!And Dave you are one of that Mega's who can change the world

author: tautech
author_rank: Super Contributor
timestamp: February 27, 2015, 09:06:27 pm
content: Welcome to the forum.I would imagine the Tek would do it, but what could be more important for accurate waveform resolution is the probing solution employed.DUT loading will not be insignificant with passive probes.

author: swartkatt
author_rank: Contributor
timestamp: February 27, 2015, 09:12:10 pm
content: Thank's for your time answering my question tautechWhich kind of a probe i should consider to buy to achieve this kind of a measurement?Will Tektronix P6202A FET Active High Impedance probe sufficient for the job?

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2015, 09:22:11 pm
content: Here's a question for you to consider and reach your own conclusions...There are different classes of test equipment, e.g. oscilloscopes, logic analysers, spectrum analysers, TDRs etc etc. Each is good at observing (and faultfinding) different classes behavious and fault.If you can assess what classes of faults (or behaviours) are going to be important to you, then you can determine what class of test equipment to buy.Example, from wired LANs. There can be "signal integrity" faults due to, for example, incorrect impedances/terminations. There can be low-level protocol faults, e.g. missing/duplicate tokens, or two devices with the same address, IP fragmentation. There can be high-level protocol faults, e.g. dropped TCP connections, excessive latency. Only the first of those would benefit from an oscilloscope; it would be difficult for a scope to find a fault at the other levels.To bring it back to your question. If you are interested in signal integrity of an DVB-ASI link then get a scope. But once you have ensured there is good signal integrity you will be debugging at "higher" levels - at which point some other equipment would be better.One technique is to assume that you alreafy have an ideal piece of equipment (e.g. oscilloscope). Then think through what you could and could not find with that equipment.

author: swartkatt
author_rank: Contributor
timestamp: February 27, 2015, 09:54:20 pm
content: Thank you for all the information tggzzzI am aware of Logic Analysers would be a better choice for this kind of a project but what i am not aware of is if it can be possible to achieve all the DVB-ASI process with a Logic Analyser under 500$? If it is possible can you give me a name of a Logic analyser solution which can handle a full DVB-ASI stream capture? The reason i am looking for an oscilloscope is if it is possible to analyse the same 214 Mbit/s stream with an oscilloscope i'd rather buy an oscilloscope than to buy a logic analyser. I think oscilloscope is a must on the bench of any electronic enthusiast.Thanks

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2015, 11:09:51 pm
content: Quote from: swartkatt on February 27, 2015, 09:54:20 pmI am not familiar with DVB-ASI, but a quick google indicates it is usually used to carry compressed audio and video data streams. If so, you need to determine whether you want to look at the audio/video, or the mpeg framing structure (or similar), or individual protocol/data data bits, or individual encoded bits on the wire. There may well be other control/negotiation protocols involved; I have no idea.A standard logic analyser would enable you to see the bits. A logic analyser with specific protocol analysis would enable you to see the frame structure. If you want to look at the video or audio then you need audio/video equipment, maybe an ear and an eye! An oscilloscope would enable you to see the voltage levels and may or may not be able to decode bits: it depends on the wire protocol and the scope's capabilities.I cannot point to any specific equipment; I will leave that to people that know what DVB-ASI involves.

author: tautech
author_rank: Super Contributor
timestamp: February 27, 2015, 11:24:48 pm
content: Quote from: swartkatt on February 27, 2015, 09:12:10 pmAn active probe was my thought, however liketggzzzI have no experience with DVB-ASI.There will be members that have, be patient others will chime in.

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2015, 11:35:06 pm
content: Quote from: tautech on February 27, 2015, 11:24:48 pmAnd if you can't afford an active probe, a low impedance Z0 probe might be sufficient (but not for differential signals).See many other threads and websites for probe information, but info I've found valuable is athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/particularly the "Formal" section.

author: swartkatt
author_rank: Contributor
timestamp: February 28, 2015, 12:02:18 am
content: Thanks again for the replays tggzzz and tautechAs in the picture i attached:I want to see this "MPEG sync byte" , "MPEG transport byte(s)", "K28,5 characters", 3 transport packet periods etc. in a real world system.I have a very long road to solve the underlying math of all this frequencies and the bits stuff in this project. What i am looking for is a good starting point with a capable equipment which will help me to see the visual representation of the technology. I do not want to play or save any of the mpeg-ts streams. I just want to see all the bits on a monitor of an equipment in a real world system.I just can not figure out what kind of an equipment will be sufficient to see this technology visually, depending on the below characteristics of DVB-ASI."DVB-ASI is carried at a 270 Mbps line rate. The 270 Mbps bit-rate on the link is derived from a 27 MHz byte clock multiplied by 10 bits. The carrier frequency of a DVB/ASI signal is 270 MHz. The maximum effective bit rate is 214 Mbit/s."I just can not make a calculation and a meaningful conclusion from the information above - what kind of an equipment is sufficient to visualize this stream.If "TEKTRONIX TDS 540A 500MHz Digital Oscilloscope" is sufficient i will buy it, if not which equipment can help me to visualize this stream?Thank you all for your answers again.

author: swartkatt
author_rank: Contributor
timestamp: February 28, 2015, 12:09:38 am
content: Thank you tggzzzWhile i was writing my last post, you sent me a post . Sorry for the inconviniece that i did not see your post until i submited mine.Anyways, thanks all for your support!

author: tggzzz
author_rank: Super Contributor
timestamp: February 28, 2015, 12:27:16 am
content: Quote from: swartkatt on February 28, 2015, 12:09:38 amA standard problem ?It looks like you are encountering a steep learning curve with many levels of abstraction to understand. Welcome to the real world! Been there,many times.Personally I doubt that having physical equipment will greatly aid understanding; at best it might confirm that you understand. I have always found that understanding comes from reading good explanations.

author: swartkatt
author_rank: Contributor
timestamp: February 28, 2015, 12:36:40 am
content: I agree with you that understanding comes from reading good explanations and it is also true that i want to have the physical equipment to confirm that i understand

author: sca
author_rank: Regular Contributor
timestamp: February 28, 2015, 01:09:56 am
content: It's a different protocol, and a different starting point, but nonetheless Mike (electricstuff)'s vids on hacking a MIPI display might give some pointers on analysing, understanding and recreating a relatively complex, up-to-date differential signal.sca

author: SL4P
author_rank: Super Contributor
timestamp: February 28, 2015, 05:46:19 am
content: Quote from: swartkatt on February 27, 2015, 08:52:55 pmThe bitrate isalways~270Mbps, but thePAYLOADis ~214Mbps + fillers.So you still want to see the whole 270 and more for edges etc.Leave trigger and headroom for jitter and other measurements as well, which severely affect the recovery of data at that speed.I see a few pieces of 2nd hand TEK test gear for SDI in various auctions, but remember this is SD... for HD, you want 1.5Gbps or higher - and ASI only comes into play as a transmission mediumaftercompression of the HD-SDI signal.Also keep in mind that early SDI signal paths won't carry ASI reliably - to do with inverted (ASI) data not being handled by earlier chipsets.

author: swartkatt
author_rank: Contributor
timestamp: February 28, 2015, 07:23:07 pm
content: Thank you SL4P and sca!

author: Neganur
author_rank: Unknown
timestamp: March 01, 2015, 01:16:36 am
content: if your bitrate is 270 Mbps and you sample at 500 MHz then your pulse width measurements will be with 2 ns resolution which is not enough to see anything meaningful.On top of that, if you want to conduct any jitter and rise time measurements I'd look for a 1 GHz scope with 2.5-5 GSa/s

author: SL4P
author_rank: Super Contributor
timestamp: March 01, 2015, 01:29:52 am
content: Sadly - these are examples why digital video test gear is not selling for small bucks.http://sg.tek.com/application/hd-sdi-videohttp://sg.tek.com/baseband-video-test-solutions

author: swartkatt
author_rank: Contributor
timestamp: March 01, 2015, 06:34:35 am
content: Thanks for the information Neganur and SL4PAn ASI signal is not like an uncompressed SD-SDI (270 Mbit/s) or HD-SDI (1.485 Gbit/s). It can carry one or multiple SD, HD or audio programs that are already compressed. An ASI signal can be at varying transmission speeds and is completely dependent on the user's engineering requirements. Generally, the ASI signal is the final product of video compression, either MPEG2 or MPEG4, ready for transmission to a transmitter or microwave system or other device. As this information provide i presume that i do not need to think much about uncompressed SD-SDI (270 Mbit/s) or HD-SDI (1.485 Gbit/s) resolutions.

author: SL4P
author_rank: Super Contributor
timestamp: March 01, 2015, 07:06:19 am
content: Correct, but keep in mind that even though SD-SDI and ASI paths are both spec'd for ~270Mbps - they are not identical as noted above. And of course... HD, where uncompressed streams ain't going nowhere!Of course completely separate to this discussion is the payload structure in the transport layer, and what broadcasters are doing to our 'once pristine' video program streams!Example: 1.5Gbps HD, is often distributed to viewers as 4-8Mbps after compression and statmuxing. 220Mbps SD programs are often packed down intto 1-3Mbps... both of which are completely unrealistic if you still want to call them 'quality' delivery methods! HD - minimum 15Mbps, SD 3-4Mbps - and that's being generous!Just to bring some reality back in -realHD origination is often pumpedliveback to base at 15Mbps or thereabouts - as a viable archive format, and transcoded down for distribution at 4-8Mbps depending on the content. Highlights etc are extracted frfom that high quaity source, and the only time you'll seeuncompressed HD is in production environments where storage capacity is not a problem, and the quality imperative as needed for post-production down to master, archive or distribution format.Broadcasters often utilise 15Mbps bandwidth for a full suite of channels 1xHD, 2xSD, some extra audio and EPG, subtitles etc... with aggressive compression and muxing - they'll squeeze a third SD 'shopping channel' in there. Also equates to easy partitioning of satellite and terrestrial 'bearers' often 32 or 45Mbps per route. (Newer bearer technology notwithstanding).Choice of optimised codecs does have benefits for specific types of content, but you have to trade-off between spatial and temporal compression... a piece of string is only 'so long' !

author: swartkatt
author_rank: Contributor
timestamp: March 01, 2015, 11:38:37 pm
content: You can reach the rest of the post at the test gear section from the link "https://www.eevblog.com/forum/testgear/what-should-be-the-minimum-oscilloscope-characteristics-for-dvb-asi-ex-43839/15/"

author: Scrts
author_rank: Frequent Contributor
timestamp: March 02, 2015, 09:34:23 am
content: I've been working in DVB field a couple of years and especially with DVB-ASI and also SDI. There's nothing to see in DVB-ASI serial stream with the scope. You may want to check the eye pattern, but you need way much better scope for that. This is basically not usable at all. If you want to check the stream, buy a proper analyzer. I think Tek have something designed for that. I've never had issues with DVB-ASI line itself as I've only used FPGA LVDS plus a buffer.The reason I am saying that you won't be able to see what's in the serial stream is because it's 8b/10b encoded. For in-depth stream analysis you can use analyzer from DecTek, which helped me most of the times.

author: swartkatt
author_rank: Contributor
timestamp: March 02, 2015, 12:52:30 pm
content: Thank you very much for the information ScrtsMay i ask you some questions on the FPGA part of the project?What kind of an FPGA you use? Part of my research i found that Altera Cyclone III series Fpgs are enough for the job.Another question i want to ask, if is it possible to use an FPGA as an equalizer deserialiser and 8b/10b decoder by itself or an external Equalizer,Serializer/Deserializer IC on the line is a necessity to use?By a proper analyzer did you mean a Logic Analyzer?DecTek products start from € 800 and for me it is such a money i would rather like to spent it for a bench equipment for my electronics hobbyThanks again!

author: Scrts
author_rank: Frequent Contributor
timestamp: March 23, 2015, 04:44:49 pm
content: Quote from: swartkatt on March 02, 2015, 12:52:30 pmAltera Cyclone II, Cyclone III and Cyclone V with their IP cores available in Megastore.Quote from: swartkatt on March 02, 2015, 12:52:30 pmThe FPGAs I've mentioned above can easily work as deserializers. The main issue is to constrain the input logic properly, but this is defined in the user manual. You'll be running two sampling clocks of 337.5MHz with 0 and 90deg phase, which will also have two additional generated inverted clocks (so 180deg and 270deg), so effectively there's 4x oversampling logic there. You need to put oversampling logic at certain places in the FPGA, close to the IO input registers. This is, again, described in the user manual. Otherwise, you won't be able to get reliable input if the FPGA will be relatively full and you'll have multiple ASI inputs and outputs. The tricky part there's also that the input is set as false path, because it's oversampled, so the timing analyzer won't show you the problem there.I've made 2xASI input to Gbit Ethernet UDP/RTP streamer (around 400Mbps max), Ethernet (7x channels) to ASI (1 channel can be selected only), have experience in designing ASI multiplexer (7x inputs, 2x outputs), modulators, etc.Quote from: swartkatt on March 02, 2015, 12:52:30 pmAll those analyzers will cost a lot. DVB is not for hobby uses. How you'll get ASI source? I expect it to be from the professional device like pro-grade SAT receiver.Bottom line:the DVB-ASI is almost dead, if not completely. Everything moves to IP and cloud based television. Maybe you want to put your effort on that? UDP/RTP based IP encapsulation is extremely easy for transmission, however it's not straightforward for reception as you'll have to recover clock from PCR.