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Bruce Trump

It’s a holiday week, Thanksgiving in USA—a good excuse for a break from techie topics. And it’s a chance to call your attention to some changes to our blogs. The title of this week’s blog is a common expression in my lexicon but these changes are good. I just thought I could get you to read if I sounded a bit grumpy.  :)

Perhaps most important is the new “subscribe” link on the right. This allows you to subscribe to email notification to The Signal or other TI blogs. There’s also a new button to email the author. I had already been providing an email at the bottom, but now there’s a link in a consistent location for all our blogs. It opens a web form in your browser so you may prefer my email link below. We’ve also made it more obvious how to leave a comment for all to see. You need to register as an E2E community member to comment (a good reason to join us), but this was not so clear in the previous page layout.

The new page layout allows more flexibility and I’m assured that there are more cool things to come—“widgets.” So watch for new, helpful thingies over on the right. I may call your attention to them later.

Another useful addition is my own.  I’ve made a table of contents page for The Signal. Many blogs tend to be “newsy” with content that eventually becomes dated. The Signal deals mostly with timeless technical issues. You may be interested in a topic that was covered six months ago but The Signal’s home page with its reverse-chronological listing gets pretty deep in multiple pages. The listings on this new page are grouped by topic on a single page—much easier to find something of interest. Check it out to find a useful topic you missed. I’ll include this link at the bottom of this and future blogs.

And what about the new graphic!?   (Thanks for the design, Pattie.)

Here’s the old one, below. I liked it, too, but I’m wondering why nobody gave me grief for the reversed “+” and “-“ on the op amp. Did you not notice or were you just too polite to comment?

I discovered this error very early but chose not to correct it, awaiting someone’s comment. To my surprise, nobody did. My colleague, John, was the only one, chiding me in a private email. I had my excuse ready—it’s actually a valid circuit. So, friends, here’s a question… what is it? As usual… please no TI peeps allowed.

I’m very thankful for many things, including your readership. Happy Thanksgiving!

Bruce       email:  thesignal@list.ti.com (Email for direct communications. Comments for all, below.)

     Table of Contents for all The Signal blogs.

Anonymous

  • Ken and Jens-Michael are correct--it's a Schmitt trigger. Or, if you prefer, a comparator with hysteresis. The name "Schmitt Trigger" seems more frequently used in digital circles while "comparator with hysteresis" appears to be more common among the analog crowd. Either way, it's a circuit with positive feedback creating a snap-action response. It's a possible future topic.

  • Indeed it seems to be a Schmitt trigger - but an inverting one.

    With the shown sine input signal, I'd say it is an inverting sine-to-rectangle converter. :)

    Unfortunately, It won't work reliably on unipolar supply.

    If you replace the GND in the feedback by an adjustable voltage and feed it with a fixed sine (or triangle) frequency, you'll have a PWM generator with variable DC. In this case, even an unipolar supply could be used.

  • It can be a Schmitt trigger. Although, I believe, if you actually walk through the ideal transfer function of an opamp, it is the same for when positive and negative feedback is used. Of course in practice, we know negative and positive feedback circuits behave differently. ;)