Triangular wave on ring oscilator - Page 1
Forum section: electronics / beginners

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 10:58:43 am
content: I recently got my first analog oscilloscope, so to start checking its integrity i built a ring oscillator, to my surprise the output from 2 of the 3 Schmitt trigger inverters are , instead of square waves , triangular, i am using only capacitors so might it be that the trigger output is getting loaded?but i am using the same capacitors so i dont know why i would have 1 of the triggers giving a propper square waveany ideas ?

author: Lee Leduc
author_rank: Regular Contributor
timestamp: May 29, 2018, 01:16:23 pm
content: Please post a schematic. People can't help without seeing your circuit.Thanks

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 01:32:20 pm
content: on each of the outputs there is a capacitor to slow the process down

author: Brumby
author_rank: Unknown
timestamp: May 29, 2018, 01:38:23 pm
content: How do you think the capacitors slow the process down?Just look at one point and think about the voltage across one of the capacitors....

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 02:00:12 pm
content: well the output circuitry of each inverter will have to charge up the capacitor before it triggers the next inverter input into going low... i guess, also without them the circuit is not precisely stable, it just outputs a bunch of noise or something too high freq for my oscilloscope

author: Brumby
author_rank: Unknown
timestamp: May 29, 2018, 02:06:23 pm
content: You should show the actual schematic of the circuit you have wired up - not a generic image with additional wording. A photo of the circuit would also do. Playing 20 questions gets very old very quick - and still may not provide the information needed.Offering answers without knowingpreciselywhat you have wired up can cause a LOT of confusion.

author: Wimberleytech
author_rank: Super Contributor
timestamp: May 29, 2018, 02:14:02 pm
content: - check your connections- check the capacitor values...all the same?- add two more stages (5 stage ring oscillator) and see if you get similar results.What part are you using? Should not matter but I am curious.What is the supply voltage?Is the supply voltage coming from a battery or a bench supply?Is this assembled on a protoboard or soldered?Are you using a 10x probe on your oscilloscope?What is the oscilloscope you are using?Take a picture of the waveform you see and post it.These questions may not all be critical, but the first step in getting help is to tell us EVERYTHING!!

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 02:53:49 pm
content: ook lets start, the oscilloscope is a promax od-416, i am using a 10x probe(oscilloscope does not have compensation for that but i can live with it) , the part number is cd40106BE, supply voltage is 12v from a linear regulator powered by a switching one.all the caps are 22nf. oscilloscope set 1uS and 2v per division (having on account the 10x)images here:https://imgur.com/a/wEfyz6C

author: Benta
author_rank: Super Contributor
timestamp: May 29, 2018, 02:59:13 pm
content: Of course they are triangular. You have a current source (the 40106 outputs hitting their current limit) charging 22 nF. What else would they be?

author: Lee Leduc
author_rank: Regular Contributor
timestamp: May 29, 2018, 03:03:32 pm
content: Here's an Appliation note using inverters in oscillator circuits.https://www.fairchildsemi.com/application-notes/AN/AN-118.pdf

author: Wimberleytech
author_rank: Super Contributor
timestamp: May 29, 2018, 03:19:45 pm
content: Quote from: Belrmar on May 29, 2018, 02:53:49 pmGreat!Your triangle waveform ramp rate is 6 volts per microsecond (deltaV/deltaT = 6e6)I = C x deltaV/deltaTI = 22e-9 x 6e6 = 132 mA The 40106 cannot deliver that much current.Therefore, I think your capacitor is not 22nF.Please show us a picture of the capacitor markings (all three side by side).Why are traces different??? Assuming the caps are all the same, consider this possibility. If you removed the caps from a tape carrier (often they come this way), I have found that there is glue reside on the terminals. This residue can insulate the wire and thus not make a connection. Make sure the terminals of the caps are clean and making good contact.

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 03:29:39 pm
content: Quote from: Wimberleytech on May 29, 2018, 03:19:45 pmagreed i made a bit of a fool of myself, the markings where 221 not 223, i should use my glasses more often

author: Wimberleytech
author_rank: Super Contributor
timestamp: May 29, 2018, 03:34:52 pm
content: Quote from: Belrmar on May 29, 2018, 03:29:39 pmAhaaa!! No problem. I wear 3x readers and sometimes even that is not enough!!Still does not answer why one of the outputs is a square wave.

author: Belrmar
author_rank: Regular Contributor
timestamp: May 29, 2018, 03:52:42 pm
content: Just used another of the ic's form my batch and this one is giving me 3 square waves.... i am a bit confused, might be some esd dmg that led to a damaged output stage? a bad puppy on the batch... no idea tbh

author: Brumby
author_rank: Unknown
timestamp: May 30, 2018, 01:44:47 am
content: With 3 caps on 3 stages, I would expect 3 triangular waveforms. 3 square waves doesn't make sense. I would be really checking the contacts of those caps.Is it still running at the same (or similar) frequency with 3 square waves?