Sine to square wave with same frequency - Page 1
Forum section: electronics / projects

author: conducteur
author_rank: Regular Contributor
timestamp: November 06, 2015, 02:42:05 pm
content: I need to convert a sine wave, from a crystal oscillator (14,31818Mhz) to a square wave, with the same frequency, to drive TTL Logic (74HCT*).Tried to drive a bc547 into saturation, to get a clipped sinewave at the collector, which is connected to +5v with a pull up resistor. Doesn't work, grabbed a second one to get a darlington pair made of 2 bc547. Doesn't work either. I checked the datasheet, and according to me, it should be able to switch 100Mhz? Or am i wrong? BD 679 doesn't work either.The sine wave is between 0 and about +5v (depends on the "load")....

author: grumpydoc
author_rank: Super Contributor
timestamp: November 06, 2015, 03:15:25 pm
content: Just feed it into a 74HCT14 or any other buffer/inverter with a Schmitt trigger input.

author: ocw
author_rank: Regular Contributor
timestamp: November 06, 2015, 03:23:20 pm
content: To see a translated version of Samuel Lawrence's sine to square wave converter go to:https://translate.google.com/translate?hl=en&sl=pt&u=http://www.bloguetronica.com/2015/09/modulo-condicionador-de-sinal-sincronos.html&prev=searchIt uses a TLV3501 as a comparator. He found that his circuit worked up to 80 MHz. I've built something similar which has worked up to 20 MHz. I haven't tested my circuit above that frequency yet.

author: dom0
author_rank: Super Contributor
timestamp: November 06, 2015, 04:01:57 pm
content: (If the 0-5 V signal swing comes directly from the crystal you are probably driving too much power into it.)If you just need a clock signal for something like a microcontroller or sequential logic, just use a 74HC14/HCT.If you don't have 74'14, but 74'04, or want better characteristics use a circuit like this:http://www.taitien.com.tw/db/pictures/modules/CMS/CMS060207001/AP20100105-Utilize%20Clipped%20Sine%20Waveform%20in%20Circuit%20Design.pdf

author: conducteur
author_rank: Regular Contributor
timestamp: November 06, 2015, 04:37:20 pm
content: If you search KCO 010T 14,31818 with google, then you'll find the part that generates the sinewave that we got from school for our project.The 74HCT14 is a good idea, so we will give it a try!

author: mark03
author_rank: Frequent Contributor
timestamp: November 06, 2015, 05:51:05 pm
content: Some oscillator mfgs suggest a circuit like this:http://www.pletronics.com/ple/articles/view/401using a feedback resistor around a logic gate. Is that equivalent to a Schmitt trigger input?

author: moffy
author_rank: Super Contributor
timestamp: November 06, 2015, 10:28:31 pm
content: Quote from: mark03 on November 06, 2015, 05:51:05 pmNo it biases the logic gate into a semi linear region and it then becomes a fairly high gain amplifier. You need to watch out though as it can pull quite a bit of current at idle because both transistors in the output stage are partially on.

author: awallin
author_rank: Frequent Contributor
timestamp: November 07, 2015, 07:44:20 am
content: see also:https://www.eevblog.com/forum/projects/10mhz-ocxo-sine-to-square/

author: rs20
author_rank: Super Contributor
timestamp: November 07, 2015, 08:20:13 am
content: Quote from: mark03 on November 06, 2015, 05:51:05 pmNo, that's anegativefeedback resistor. Schmitt trigger makes use ofpositivefeedback.

author: dom0
author_rank: Super Contributor
timestamp: November 07, 2015, 10:45:06 am
content: Quote from: rs20 on November 07, 2015, 08:20:13 amIt's no feedback at all at the working frequency. The 1 M? bias the gate.

author: rs20
author_rank: Super Contributor
timestamp: November 07, 2015, 11:08:23 am
content: Quote from: dom0 on November 07, 2015, 10:45:06 am...via negative feedback at DC

author: bloguetronica
author_rank: Frequent Contributor
timestamp: June 04, 2019, 03:30:56 am
content: Quote from: ocw on November 06, 2015, 03:23:20 pmAppreciated. Thanks!Kind regards, Samuel Lourenço

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 06, 2019, 01:00:16 pm
content: Other way it can be done (I have seen this done at high frequencies) is simply have very, very fast amplifiers, and put many of them in series. As the signal get bigger and bigger you will hit the rails and approach clipping.But in this case: Schmitt trigger is probably the best approach.