Active analog delay line for composite video? - Page 1
Forum section: electronics / beginners

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 23, 2019, 05:54:13 am
content: Hey guys!.So I have this project that basically needs to delay composite video signal(NTSC and PAL) at least 1 scan line.Now I came across Piezo delay lines used for pal line memory.But they are not available and bit too big?.Now other solution would be a passive delay line with lumped elements but I would like to have a more compact design.Would it be possible to create a active filter with flatter group and phase delay(of about 64us I guess).My current idea is a Opamps(or cascaded) in perhaps Bessel filter?.any idea guys?.Thanks in advance!

author: vk6zgo
author_rank: Super Contributor
timestamp: August 23, 2019, 08:44:33 am
content: I think if there were easier ways, the TV receiver makers would have used them, but they opted for the piezo ones as the most compact option.You could digitise the video line, store it for 64 uSecs, read it out & convert it back to analog--- this was actually done in some broadcasting equipment.(a "line" store, as distinct from the more well known "frame store".Or maybe use something like a "bucket brigade " device.

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 23, 2019, 09:56:01 am
content: Hey thanks for the replay.The thing is I NEED to keep this in analog domain.I already looked into BBDs but those dont have enough bandwidth to handle video.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 23, 2019, 10:15:37 am
content: Can you use a TDA4660?

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 23, 2019, 10:45:03 am
content: WOaaHH! How Did I miss THAT!!...Thanks Man ! I am reading it now.

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 23, 2019, 11:09:22 am
content: That actually seems to do the trick!.But its clocked with the sand castle pulse but can it be synced with HSYNC instead it says the clock is ''line frequent'' dependent. HSYNC is pretty line frequent right??. it says it for color-difference outputs of chroma decoders but since its in the same base band as full NTSC or pal Feeding a pal or NTSC should yield the same result(64us) delayed right?

author: macboy
author_rank: Super Contributor
timestamp: August 23, 2019, 03:23:09 pm
content: This is not a problem that you need to re-engineer a solution to. All PAL TVs (and probably most PAL video equipment) contain at least one 64 us delay line, used for the two-line averaging color correction. Typically these use a Pizeoelectric or ultrasonic delay line. Seehttps://en.wikipedia.org/wiki/Delay_line_memory#Piezoelectric_delay_linesto get started.

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 24, 2019, 08:03:44 am
content: But those piezoelectric stuff is bit large so the baseband delay chip is still smaller even if it's a dip in.the question now for me is can u sync it with a hsync pulse or would it need to be phase with the line since pal alternate the phase each line.I am stuck on the sandcastle signal a sync separate r with sandcastle out is even larger so any ideas?

author: mikerj
author_rank: Super Contributor
timestamp: August 24, 2019, 11:14:28 am
content: Quote from: macboy on August 23, 2019, 03:23:09 pmThe OP is well aware of acoustic delay lines, as mentioned in his first post. He wants a smaller and more robust solution.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 24, 2019, 01:44:59 pm
content: One small problem with devices originally intended to delay colour U & V signals is that the bandwidth of these is around 1.3 MHz, compared to 5 MHz for the Composite signal.As human eyesight does not have as high a resolution for colours as it does for "Black & White" (Luma), it is possible to use a lower bandwidth signal for the colour information, simplifying the transmission system.As the devices are not specified for the wider bandwidth signal, errors may ocurr in the delay with a full composite signal

author: xtr0d3m0n
author_rank: Newbie
timestamp: August 26, 2019, 04:28:58 am
content: Ooops.....seems like I will run into bandwidth issues,But these chips or so compact especially U3665M.We can only hope that these can go a little bit over the BW specs but Those also have LPFs to filter out out of band noise so they might just filter out everything after 1.3MHz. Since these babies are cheap on aliexpress I think I will try it anyways after reading all the datasheets.Do you guys think its worth it?

author: xtr0d3m0n
author_rank: Newbie
timestamp: April 07, 2020, 03:21:17 am
content: Hi so a year later still on the search I came across the "1 H" delay line chips which seems to be using CCD and some times with cmos together on the fan process.which if I am not mistaken should do the trick.1 H stands for 1 horizontal lines right? Here some chips.https://pdf1.alldatasheet.com/datasheet-pdf/view/47154/SONY/CXL1506M.htmlhttps://html.alldatasheet.com/html-pdf/41182/SANYO/LC89962M/127/1/LC89962M.htmlCan anybody confirm this will work?