Generic fast comparators - Page 1
Forum section: electronics / beginners

author: Buriedcode
author_rank: Super Contributor
timestamp: October 09, 2020, 10:26:48 pm
content: I posted this in the beginners section, as its a fairly vague question.For random home projects and general tinkering I know of, and have plenty, of generic parts, discretes, opamps, logic, micros etc.. but aside from the old LM393 I don't have any comparators.Recently I've been toying with making my own inductor/transformer (ferrite) tester, which is more for a DIY project than actual serious measurements, and everything I've come up with calls for a fairly fast comparator to square up waves for period measurement. I'm talking 1MHz switching max, perhaps with pulse widths down to 100ns, preferably down to 3.3V, but 5V min would be fine.Are there any go-to, or common high speed comparators? The selection on Farnell/RS is pretty big, and I could just order a bunch based on specs and price, but I was also curious if anyone had specific parts they regularly use?

author: fourfathom
author_rank: Super Contributor
timestamp: October 10, 2020, 12:03:56 am
content: I don't know if these are common or generic, but for a Time Interval Counter I am making, inputs up to a couple hundred MHz, I used the TLV3501 comparator from Texas Instruments. The TLV3502 is a dual comparator. These are available in a couple of different surface-mount packages, have a 2.7V - 5.5V supply range, and draw about 3.2 mA. They seem OK to me.

author: pwlps
author_rank: Frequent Contributor
timestamp: October 10, 2020, 12:15:39 am
content: I don't know what you mean by generic but for fast switching at 1-2 MHz I was recently using the LT1394 from Analog Devices. Single 5V or +/-5V, 7ns.Edit:AD has a nice page with all their fast comparators, including prices:https://www.analog.com/en/products/analog-functions/comparators/high-speed-comparators-lessthan-100ns-propagation-delay.htmlI'm not advertising for AD, it was just faster than navigating through RS/Farnel selection menus.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 10, 2020, 12:30:43 am
content: You're right, generic probably isn't the right word (as it implies things like LM358 or very old designs made by many manufactures), I guess the closest would be "common" or something to have a few of in stock to fill the gap/need. Obviously the more specific the need, the more specific the part, but for reasonably quick prototypes, its nice to have some parts to get something working.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 10, 2020, 01:28:52 am
content: The only other generic, plain vanilla, ubiquitous, low cost and as old as the the Roman Colosseum, is the LM311.It is a single comparator, but it has additional features.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 10, 2020, 08:23:22 am
content: IME, the best way to find "generic" components is to sort by lowest price and highest availability at a few different distributors. You can then add your constraints because very seldom you just want the "most generic" part withoutanyspecific requirements.This way, you avoid the social bias and find parts that areactuallypopular in the industry. Some can be quite modern; instead, by asking around, you'll get suggestions mostly regarding parts from the 1980's or even 1970's.Bonus points: look if a very similar part is available in the same package and same pinout from a different manufacturer; possibly under a different part number and slightly different specifications.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 10, 2020, 08:53:21 pm
content: Quote from: fourfathom on October 10, 2020, 12:03:56 amThanks for this, ordered a bunch. The dual version has a nice pinout for prototyping and its ideal for low voltage systems.Although the specs of their analogue parts tend to be nothing special, had look at microchips offerings. The MCP6562 is pretty low power, very cheap, but not quite fast enough for some projects, but certainly a half decent speed upgrade (60ns) from the 393 in 5V systems.For higher voltage systems (12 - 15V) it looks like the fastest "reasonably" priced option is the old LM319 (80ns, approaching 100ns for lower overdrive). And Farnell has the KA319D going for £0.07... Worth at least adding to the next order.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 10, 2020, 09:58:25 pm
content: I use MCP6562 on a regular basis: reasonably cheap, 5V max, low power, faster than 393. Also has a SPICE model,anda corrected 3f5-compatible model here:https://www.seventransistorlabs.com/Modeling/SPICE/MCP6561.cktThere's not much reason for higher voltage circuits these days, I don't mind making controls (on the rare occasion I need a discrete controller) at 3.3 or 5V supplies. It's just gain or level shifting to get to any physical interface (e.g. 12V gate drivers, +/-15V analog I/O, etc.).Any faster than that and you're into the <= 7ns families (not really anything inbetween, for some reason). I don't think there's anything really "generic" here, just shop around and find what works. (I haven't shopped this for a while, I don't have any suggestions offhand.)Also if you need a lot of speed at low cost, consider ECL, LVDS or other differential receivers -- they aren't specified as comparators, primarily because the offset voltage could be anything (often, up to 100mV). Typical parts may perform well enough for your application; if you can incorporate self calibration, all the better. Remember to check for wide CM input range: some receivers are hardly differential at all, they have so little range! (Particularly a problem with integrated receivers, in high speed ADCs, some FPGAs, etc. Read the datasheet carefully!)Tim

author: tggzzz
author_rank: Super Contributor
timestamp: October 10, 2020, 10:24:57 pm
content: Quote from: Buriedcode on October 09, 2020, 10:26:48 pmOnce you are asking questions like that, you would benfitfro The Art of Electronics. In this case see tables 12.1 and 12.2.If nothing else, it clarifies the parameters that can be considered.

author: David Hess
author_rank: Super Contributor
timestamp: October 11, 2020, 10:47:15 pm
content: The LM311 is the common comparator faster than the LM393/LM339.My choice for a part faster than the LM311 would be the 10 nanosecond LT1016 or LT1116 (PNP input single supply), because they are stable in their linear range making them a little more forgiving.Another type of part to consider, especially if you want a bunch of fast comparators in a single package, are differential line receivers.