Fanout buffer for high speed differential signal, few suggestions - Page 1
Forum section: electronics / projects

author: VEGETA
author_rank: Super Contributor
timestamp: October 27, 2021, 11:04:08 pm
content: Hello,I have an IC which outputs 8-lanes (lane = diff. pair = transmission line) of VBO-HS video to an HDMI transmitter IC which converts this VBO-HS to HDMI 2.0.Depending on chosen video resolution, number of lanes are determined with 8-lanes being a maximum of 4k @ 60fps.However, I want to output an analog video of that VBO-HS source at the same time with the HDMI, I took care of everything related to it such as video DAC (ADV7343), VBO-HS to parallel converter (THCV218) and so on... all left is an IC which splits\distributes\fanouts only the first 2 lanes.maximum analog video needed is about 1080p so 2 lanes are necessary. each lane has a maximum of 4 gbps so the fanout IC should be capable of that.I already routed the 8 lanes into the HDMI transmitter using length matching and impedance matching as they required but now I need to cut 2 lanes out and put the fanout ICs in the middle, please look at attached image.My questions are:1- what lengths to choose for the 2 lanes? I mean2- how to place and route this?3- what about skew? I have no info on acceptable skew of the HDMI TX IC but I cannot have fanout ICs on all lanes.4- does internal termination resistor of fanout IC do any bad to output signals?Here are my suggested fanout ICs:PI6C5916004 -> 2 ICs per board = 200 per 100 board @ about 4$ price per IC which is about the cheapest to get. it doesn't look like to be available in all famous distros. it has 4 outputs but I only need 2. it has skew of 30ps but part-to-part skew is 200ps which is a lot.PI6C5946002 -> exactly as above but not available from distros and 3.5k minimum quantity which is impossible to me.THCV2712 -> official one from Thine (VBO-HS creator) but it is just a fanout IC, very pricey at 8$ per IC. it has 20 ps of skew which for now taken as minimum requirement.ADCLK944BCPZ-R7 -> seems good from analog devices. but part-to-part skew is 35ps.NB7L14MN1TWG -> pricey but has < 15 ps skew, and 50ps part-to-part skew.SY58013U -> very pricey but also < 15 ps skew and 100ps part-to-part skew.NOTE: I searched in Digikey assuming frequency is >= 4.5 GHZ since they don't offer GBPS.Other parts:SY58606U -> has 3 GHZ but 4.25 GBPS capability. skew is 15ps and 100ps. this is my current choice, price is about 4.5$ per unit which means 9$ per board @ 100 boards... damn it is so pricey, but looks like this is the way it is.Looking forward to your help!best regards

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 01:39:35 am
content: Hello,so far SY58606U is the fanout IC, gonna have 2 for 2 lanes.I just need your help in routing and skew stuff + any other recommendation.

author: BrianHG
author_rank: Super Contributor
timestamp: October 29, 2021, 02:15:55 am
content: Not a fanout IC, but a 4 channel differential amp & LVDS to HDMI TMDS converter IC.PTN3366 1$, 3GHz, plus a level converter for the HDMI I2C and hotplug detect.Can amplify/input 0.5v LVDS through 3.3v LVDS and output proper HDMI TMDS levels.No logic, all analog.+ Built in ESD protection. no funny traces and components between the IC and HDMI port.I think 6GHz versions now exist.

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 03:23:01 am
content: Quote from: BrianHG on October 29, 2021, 02:15:55 amI don't want this functionality but rather to duplicate the input differential signal into 2 independent outputs, one goes to HDMI TX IC and the other to the video DAC circuitry.The application does not require any level shifting, output from ASIC is VBO-HS which goes into the HDMI TX IC. The required fanout will be in the middle, taking VBO-HS from the ASIC then duplicating it.. one duplicate output goes to HDMI TX IC, and the other to analog video DAC circuitry.Do you have a suggestion here?HDMI TX IC + ESD protection all taken care of.

author: BrianHG
author_rank: Super Contributor
timestamp: October 29, 2021, 03:31:31 am
content: Do your calculation on drive, load of the 2 destinations and where and how you provide termination. You may not need any IC to keep everything in spec. You need a specialist and quality PCBs to operate here. One thing I do know is in such system, you feed the 2 destination ICs in series, not a Y split.Yes, a 1:2 amp helps give you play room or additional layout options.

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 03:44:02 am
content: Quote from: BrianHG on October 29, 2021, 03:31:31 amCan you post an example using my image above? I don't quite get what you mean.I am not familiar with Y split but I am going to need it when I do the 4 DDR3 RAM ICs. My PCB is based on Allpcb 4-layer stack with their thickness and so on, can't change that since there are many length and impedance matching based on it.I am using KiCAD and there are no calculation tools. HDMI IC should have a skew margin but the company's support still didn't respond to my question. They mentioned I might get away without switch\1:2 IC but generally recommended the 1:2 or switch IC.

author: BrianHG
author_rank: Super Contributor
timestamp: October 29, 2021, 04:08:12 pm
content: Have you considered HDMI splitters like the passive bidirectional TI HD3SS215 or active amplified Diodes Inc HD3SS215.

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 04:16:53 pm
content: Quote from: BrianHG on October 29, 2021, 04:08:12 pmthese appeared in my search but it is a switch not a duplicator or split, meaning only one output is active at a time and you get to choose which one.what I need is one input -> 2 active independent outputs.you wrote the same part number for both.

author: BrianHG
author_rank: Super Contributor
timestamp: October 29, 2021, 04:36:02 pm
content: Sorry, I meant diodes inc PI3HDX412BD.

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 04:50:19 pm
content: Quote from: BrianHG on October 29, 2021, 04:36:02 pmthis is only for HDMI 1.4 but the required data rate for me is 4 gbps, this one can only do up to 3.4 or something. I need it to be 4 gbps.you can look at my previous microchip part (and the ones posted above it), isn't it good?I tried searching for hdmi 2.0 splitter but could not find one.

author: BrianHG
author_rank: Super Contributor
timestamp: October 29, 2021, 05:33:28 pm
content: Isn't the microchip part a single channel?It will be a wiring nightmare to get right.Your spec of 4GHz is in a mid tier location where part availability goes down and price goes up.You also will need tools to verify your PCB unless you have CAD tools and manufacturer specs down to a 'T'.Too bad about the PI3HDX412BD.

author: VEGETA
author_rank: Super Contributor
timestamp: October 29, 2021, 05:50:02 pm
content: Quote from: BrianHG on October 29, 2021, 05:33:28 pmmicrochip part is single channel with the channel being a diff. pair, so it works but I need 2 of it. price-wise, getting 2 is kinda ok but I hoped for better.how to verify?should I be matching the length as usual? meaning from cap to fanout ic and then to hdmi tx should be the same as other lanes which are from cap to hdmi ic directly? I based the design on allpcb 4-layer stack but should I tell them something once I want to manufacture? I guess if i went with others I can choose custom stackI found this:DS100MB203but it is so pricey at 20$!!

author: VEGETA
author_rank: Super Contributor
timestamp: October 30, 2021, 02:13:02 am
content: TI support suggested using this part: DS64MB201, I also got cheaper ones like DS42MB200 and DS40MB200.These have propagation delay of about 200 ps max while microchip one has max 320ps, official THCV2712 mentions 150 ps typical.This way the 2 lanes will be 250ps delayed from the other 6 lanes, and since HDMI Tx IC support still didn't inform me about their propagation delay and skew margin values... I don't know what to do.MORE: I've been thinking of guessing the propagation delay margin allowed, and got this idea:maximum rate = 4 gbps -> 1/4gbps = 0.25 nS = 250 ps. effectively it won't be 4 gbps but about 3.5, so time duration will be ~0.29 ns = 290 ps. So maybe if propagation delay was <= 250ps it will be fine. is this correct understanding or just plain stupid?

author: ejeffrey
author_rank: Super Contributor
timestamp: October 30, 2021, 03:22:05 am
content: I'm not sure how that particular standard works, but other multi channel transceiver systems have relatively lax requirements on matching between lanes, usually at least several nanoseconds. Each lane goes through clock and data recovery as well as deserialization independently. Then there is some amount of buffering for realignment.150 picosecond skew between lanes would be no problem on something like pcie or a 10G network transceiver. I'd guess it is fine here too but you would have to look at the spec to be sure.

author: VEGETA
author_rank: Super Contributor
timestamp: October 30, 2021, 02:04:41 pm
content: Quote from: ejeffrey on October 30, 2021, 03:22:05 amI am not sure either since this part of the standard is not freely available.maximum effective data rate is about 3.5 gbps, so if you say 10G are ok with several nano seconds then this must be ok.

author: VEGETA
author_rank: Super Contributor
timestamp: October 31, 2021, 08:09:18 am
content: Currently I am going with this: DS64MB201 since it can do both lanes in 1 IC. still around 11$ FFS!!!So I am going like this for my digital video to analog video circuit:VBO-HS signal from ASIC -> DS64MB201 -> THCV218 (VBO-HS to parallel converter) -> ADV7343 (video DAC) -> output connector + LM1881 sync stripper.I2S audio before it goes to the HDMI TX IC -> PI6CV304WE (x3 of it to fanout I2S, one set for HDMI TX IC and the other for analog audio) -> PCM1754/PCM5100A (audio DACs).this will be around 50$ in parts which is very expensive parts to add. the product is already very expensive to make even without this... about 400$ to make (approx. calculations for 100 boards).I wonder if I can just getaway without using any fanout buffer but just take the VBO-HS from ASIC then to a via (already exist due to layout), then fork 2 forks, one for HDMI TX and one for analog video circuitry. How about this?I saw this method done for laying out DDR3 RAM 4 ICs, the address signals... which is in the support documents of the ASIC chip I am using.I've never been this much confused X_Xthe product is a 4k60 video scaler which takes all analog input video sources (CVBS, S-video, Component, RGB, VGA) and 4k60 HDMI then converts them to HDMI outputs, 2 independent outputs which are scaled (up to 4k60) or downscaled (down to 240p). this topic was about adding an analog video output besides all that. It is tailored for games, retro gamers in particular.Assuming all this was approved and got to 500$ cost, then selling it for 700$ is the least to do but 700 is very pricey and I doubt people will be that interested, even if the cheapest ever 4k60 scaler from Extron is about 1500$.what do you think?