ECL to TTL - Page 1
Forum section: electronics / projects

author: macona
author_rank: Regular Contributor
timestamp: September 22, 2025, 04:36:24 am
content: Does anyone know much about PECL? I am wanting to make an interface for my Zygo interferometer laser head. They have differential PECL out and I need TTL to go into the uC. I am planning on using Sam's uMD2 display hardware and softwarehttps://www.repairfaq.org/sam/uMD2/uMD2.htmThe interface uses a couple UA9637 line receivers but im not sure how well that will work with PECL Or should I just redesign and use something like a SN65ELT21DGKR which I can find stock of.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 22, 2025, 06:13:10 am
content: You can also use a fast rail to rail comparator here, compare their price with the translator part.

author: ch_scr
author_rank: Frequent Contributor
timestamp: September 22, 2025, 08:28:47 am
content: There is this example from the Motorola AN-581 for simple discrete conversion circuit.Maybe a 1:4 transformer and some passives could be used as well for a different trade-off, making full use of the differential output.There are other equivalent translator IC's from different manufacturers, e.g. MC100ELT21, SY100ELT21.There are a lot of (quite old) application notes regarding ECL that are partially applicable to PECL.Take care to not confuse PECL and LVPECL, while the swing is similar the "common mode" voltage is quite different (incompatible).

author: Benta
author_rank: Super Contributor
timestamp: September 22, 2025, 10:24:26 am
content: ON Semiconductor has a good offering:https://www.onsemi.com/products/timing-logic-memory/clock-data-distribution/translators

author: David Hess
author_rank: Super Contributor
timestamp: September 22, 2025, 04:14:39 pm
content: The UA9637 datasheet recommends a common-mode input voltage range of +/-7 volts when using a 5 volt supply, so I think it will work fine.

author: macona
author_rank: Regular Contributor
timestamp: September 22, 2025, 06:30:01 pm
content: Thanks everyone. The part I mentioned is only a couple bucks a piece so it's not a big deal. I'll try the board with the UA9637 as is and see if it works. If I dont get a signal out I'll mod in the dedicated IC.

author: David Hess
author_rank: Super Contributor
timestamp: September 22, 2025, 11:10:11 pm
content: Tektronix did several fully documented designs using TTL and PECL, but tended to use discrete level shifters. Still, there is something to learn there if you have to go with a discrete design. TTL was pretty slow back then so they did not require a lot of performance.The usual suspects who made TTL published application notes on level shifting to ECL.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: September 23, 2025, 02:50:21 am
content: Quote from: macona on September 22, 2025, 04:36:24 amThe interferometer head (and reference from the laser) output an AC signal, usually in the 1 - 2 MHz range, so speed is not an issue.The HP 10780 read heads provide a > 2.5 V swing, so I'm surprised that Zygo went with PECL.Nonetheless, differential PECL should work with the receivers on the uMD2, but you would have to provide termination resistors.