Building a Fast Edge Square Wave Generator

RE: Building a Fast Edge Square Wave Generator

embeddedguy — Sat, 17 Apr 2021 08:27:14 GMT

Nice! So you don't need MCU for doing this.

RE: Building a Fast Edge Square Wave Generator

fmilburn — Fri, 16 Apr 2021 17:51:07 GMT

Hi Shabaz,

I really enjoyed this project and learned a lot. I am curious about what you think about adding variable output frequency to the circuit controlled by a microcontroller. Perhaps using a DDS chip like the AD9850 DDS Synthesizer to replace the oscillator. I'm not sure how to read the datasheet of the AD9850 on rise / fall time but it appears your circuit is much faster. Would something like that work?

Frank

edit: or perhaps just use the uC clock

RE: Building a Fast Edge Square Wave Generator

shabaz — Fri, 16 Apr 2021 12:28:55 GMT

Just a quick update on this project..

I wasn't expecting it, but the PCB version turned out to be faster.. or maybe it's the particular IC that I used.. this one: MC74AC02DGMC74AC02DG

Now the rise-time is 500 ps, and the fall-time is around 420 ps.

This was tested with a 5V DC supply.

[View:/resized-image/__size/620x475/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7edbcc91-1387-4d28-9bfb-5c21ca2b6f04/2451.contentimage_5F00_207643.jpg:620:475]

RE: Building a Fast Edge Square Wave Generator

three-phase — Sat, 06 Feb 2021 20:47:19 GMT

Nice project and well implemented. I went down the official route and purchased a pulse generator from Leo Bodnar when I wanted to check the performance of instruments.

Kind regards.

RE: Building a Fast Edge Square Wave Generator

DAB — Sat, 06 Feb 2021 19:22:38 GMT

Nice build.

DAB

RE: Building a Fast Edge Square Wave Generator

neilk — Sat, 06 Feb 2021 16:28:27 GMT

shabaz,

Nice little project with a great result.

Please can yo do a quick blog about the prototyping technique with adhesive copper tapr and Kapton tape??

Neil

RE: Building a Fast Edge Square Wave Generator

jc2048 — Sat, 06 Feb 2021 15:35:23 GMT

That looks like good fun. A nice project.

I, too, like the prototype method. Although I carve up pcb board, I hadn't thought of adding supply rails.

AC logic is impressive, though keep in mind can also be a bit of a liability (from an EMC point of view

because of the edge rates) if you don't actually need it.

With my scope (200MHz) I don't have the capability to look at rise times like that, but I was curious how

AC logic compares to the output drivers in a modern microcontroller, so I've done essentially the same

thing as you with a UNO.

[View:/resized-image/__size/400x300/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7edbcc91-1387-4d28-9bfb-5c21ca2b6f04/contentimage_5F00_207640.jpg:400:300]

The outputs I've chosen are all on the same port, so I can switch them all simultaneously. This is down a

1m length of 50R coax with a 'T' piece and a 50R terminator at the end [my crummy scope doesn't do 50R

inputs, worst luck].

[View:/resized-image/__size/480x234/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7edbcc91-1387-4d28-9bfb-5c21ca2b6f04/contentimage_5F00_207641.png:480:234][View:/resized-image/__size/480x234/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-7edbcc91-1387-4d28-9bfb-5c21ca2b6f04/contentimage_5F00_207642.png:480:234]

Resistors are 180R [that was based on the idea that the MOSFETs in the Atmel part are probably around the

20R area for rds(on): I'm obviously not too far out, as I'm getting the 2.5V you'd expect with a 5V supply

and series termination at the drive end of the cable].

So yours is a good ten times quicker. You win! (But then you always were going to.)

RE: Building a Fast Edge Square Wave Generator

michaelkellett — Sat, 06 Feb 2021 09:11:18 GMT

Useful tips here Shabaz - thanks.

I managed to buy an HP8082A at an auction for about £75 a couple of years ago - it can do 1ns edges (fastest it can do) but it's huge and old and won't be eay to fix if it ever goes wrong.

RE: Building a Fast Edge Square Wave Generator

14rhb — Sat, 06 Feb 2021 08:42:57 GMT

Aside from the project aim, which is very interesting as well, I particularly like your prototype method of Kapton and copper tapes.

RE: Building a Fast Edge Square Wave Generator

jw0752 — Sat, 06 Feb 2021 05:24:31 GMT

Cool project. Once I catch up a little I will have to give it a try.

John

RE: Building a Fast Edge Square Wave Generator

genebren — Sat, 06 Feb 2021 02:18:07 GMT

Nice experiment/test. I hope that this device will serve you well in your future experiments.