Previous in Forum: Operational Technology Security Procedure   Next in Forum: EDC
Close
Close
Close
60 comments
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49

How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 8:56 AM

HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

I THINK VDC SUPPLY IS JUST FOR POWER UP THE CIRCUIT AND IT'S NOT A INPUT SIGNAL.

__________________
Success is a wall made by bricks called failures.
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30461
Good Answers: 819
#1

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:25 AM

Do turn off Caps Lock.

An oscillator is inherently unstable, which is why it oscillates. If it required an input, it wouldn't be called an oscillator.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 2)
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#4
In reply to #1

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:34 AM

that means because of that unstability it's getting the output ur saying?

__________________
Success is a wall made by bricks called failures.
Register to Reply Score 1 for Off Topic
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30461
Good Answers: 819
#10
In reply to #4

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 3:28 PM

<...ur...> does not exist in the English language.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru

Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1676
Good Answers: 122
#2

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:31 AM

Because in some oscillators the TTL (Transistor-Transistor-Logic) circuitry is designed to produce an oscillated output utilizing the VDC as the source and output.

You must examine and analyze the oscillator circuitry carefully in detail to fully understand it's operation.

Break the circuit up into sections, identify what the resultant signal will be at each section, then visualize or better yet; draw the suspected waveform beside each test point so that you can see the affect being impressed on the waveform as it progresses through the circuitry. (Suggested minimum sections are input, conditioning, and output however the conditioning section should be broken up into additional sections if you really want to understand the operation.)

If possible obtain an oscilloscope and probe each test point to evaluate whether your calculations are correct or not by comparing the measured waveform against your drawing(s).

__________________
They said; "Brain size?" I heard; "Train size?" so I said: "I'll take a small one, thank you."
Register to Reply
5
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#3

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:31 AM

First, a quick lesson in netiquet. Turn your Caps Lock off. Writing in all capital letters is considered to be SHOUTING and rude behavior.

You've asked a very astute question that is difficult to completely explain without a solid foundation in circuit theory, filter design, stability theory and the linear mathematics involved.

You are correct that the power supply is not the source of the oscillation however it is the source of the power to sustain the oscillation. What actually starts an oscillator to run is a transient signal disturbing the resonant circuit. Most often this transient comes from the noise produced by a resistor, semiconductor or external interference.

If one constructs one of the tried and true oscillator designs (Colpitts) it will just produce the desired oscillation. However, if one builds this circuit in most circuit simulators it will not oscillate. The circuit simulator works with ideal parts that have no noise components. Some simulators do a separate noise production calculation in a different mode but this mode will not induce a steady state oscillation. If one alters the circuit so that a small impulse happens in the resonant circuit after start up in a simulator, then suddenly after that impulse an oscillation will happen.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply Good Answer (Score 5)
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#5
In reply to #3

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:39 AM

Can u say in single word, is that due to "resonance" or "noise" or anything else?

__________________
Success is a wall made by bricks called failures.
Register to Reply Score 1 for Off Topic
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#6
In reply to #5

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 9:49 AM

No I cannot say this in a single word. Complicated things cannot be said in a single word. If they could then they wouldn't be complicated.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: Oct 2008
Posts: 42293
Good Answers: 1663
#7
In reply to #6

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 1:03 PM

I think you could answer in a single word.

"No".

I think out friend needs to hit the books.

vijay guntimadugu these are for you to read.

oscillator basics - Electronics Tutorials

Oscillators-Tutorials-Circuits-Types and Applications

Register to Reply
Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
Posts: 8778
Good Answers: 376
#8
In reply to #5

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 1:59 PM

How about a helpful link instead.

http://en.wikipedia.org/wiki/Electronic_oscillator

__________________
jack of all trades
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30461
Good Answers: 819
#11
In reply to #5

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 3:32 PM

It is impossible to say anything of any depth with a single word.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Oct 2008
Posts: 42293
Good Answers: 1663
#12
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 3:35 PM

Well...........................................................maybe.

Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#13
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 4:20 PM

True.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
Posts: 8778
Good Answers: 376
#14
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 4:40 PM

Three possibly. How about "amplified opamp instability". Sort of big picture helpful although also sort of four words.

__________________
jack of all trades
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#32
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/04/2015 12:16 PM

I could say things 'of great depth' about some people on CR4 using a single word.

I could, but I won't, it would be .... 'impolite.'

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply Off Topic (Score 5)
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7369
Good Answers: 427
#48
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/06/2015 12:51 PM

What about "ballocks". That can cover a great deal of depth. One of my colleagues (OK he was my boss), LtCol Millen was very fond of the term.

Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21005
Good Answers: 781
#51
In reply to #11

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/08/2015 2:14 PM

"Profundity"

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply Score 1 for Good Answer
Member

Join Date: Feb 2015
Location: Colorado, U.S.A.
Posts: 6
Good Answers: 1
#20
In reply to #5

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/03/2015 10:40 PM

Don't appear to be many old ham radio operators on here. Rickster has the best one-word answer, "feedback". Although, in some cases where high accuracy is required, a quartz crystal is used as we used to do in ham radio. The crystal is excited by an imposed voltage and oscillates at a specific frequency that is amplified by the tube or transistor in the circuit.

Register to Reply
Power-User

Join Date: Feb 2007
Posts: 276
Good Answers: 25
#21
In reply to #20

Re: HOW AN OSCILLATOR GETS OUTPUT WITHOUT GIVING INPUT SIGNAL?

03/04/2015 12:03 AM

Dit dit.

Register to Reply
Guru
Hobbies - Fishing - Old Salt Hobbies - CNC - New Member United States - US - Statue of Liberty - New Member

Join Date: Mar 2007
Location: Rosedale, Maryland USA
Posts: 5198
Good Answers: 266
#9

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 2:50 PM

Quartz Crystal

__________________
Life is not a journey to the grave with the intention of arriving in a pretty, pristine body but rather to come sliding in sideways, all used up and exclaiming, "Wow, what a ride!"
Register to Reply
Guru

Join Date: Jul 2006
Location: Silicon Valley
Posts: 5356
Good Answers: 49
#15
In reply to #9

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 7:24 PM

So if an oscillator needs an input signal, where did that signal come from, "Another oscillator?" And then where did that input signal come from? On-and-on...

Isn't this a little like if God made the Universe, who made him, etc..

__________________
"Perplexity is the beginning of dementia" - Professor Coriolus
Register to Reply
Guru
New Zealand - Member - Kiwi Popular Science - Weaponology - New Member Engineering Fields - Power Engineering - New Member Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: Auckland, New Zealand
Posts: 8778
Good Answers: 376
#16
In reply to #15

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 7:40 PM

Soooooooo, you think the universe is fundamentally made up of oscillations? I see you are in the unified wave field theory camp.

__________________
jack of all trades
Register to Reply Off Topic (Score 5)
Guru

Join Date: Oct 2008
Posts: 42293
Good Answers: 1663
#18
In reply to #15

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 8:30 PM

The egg came before the chicken.

Register to Reply
Guru

Join Date: Jul 2006
Location: Silicon Valley
Posts: 5356
Good Answers: 49
#19
In reply to #18

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 9:10 PM

This answers an age old...

Q: "If God is all powerful, can he make a rock so big that even he can't lift it?"

A: "No, but he can make a rock so big that his doctor advises him against trying to lift it."

__________________
"Perplexity is the beginning of dementia" - Professor Coriolus
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#25
In reply to #15

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 9:31 AM

"You can't fool me, it's turtles all the way down."

You want a simple oscillator, here's one:

Pick up some TTL 74LS07 chips, (Hex inverter chips, the 'hex' revers to how many inverters are on the chip, like a 'quad NAND gate' chip has four NAND gates on it). Do NOT supply power to the circuit until instructed to. Wire the chips up to the power and ground buses, then daisy-chain the inverters, output to input, until you have an odd number of inverters in a chain. Not take the last output and wire it to the input of the first inverter, connect an oscilliscope to some point in the chain (does not matter where) then supply power to the circuit.

Note the signal on the oscilliscope.

How does this work? Let's look at it through Boolean Algebra, with a simple circuit, only three inverters, labeled X, Y, and Z.

connected in a ringeach inverter's equation is as thus:

X = NOT (Y)

Y = NOT (Z)

Z = NOT (X)

Now we can do algebraic substitution:

X = NOT ( NOT (Z) ) -> X = Z

Y = NOT ( NOT (X) ) -> Y = X

Z = NOT ( NOT (Y) ) -> Z = Y

And one more time:

X = NOT (X)

Y = NOT (Y)

Z = NOT (Z)

Each inverter is supposed to be the opposite of ITSELF, which is

impossible in a static state. but it tells us what the gates are doing if we look at it dynamically.

In the real circuit, it takes time for each gate to change, and this delay adds up, causing the rapid self-flipping to stabilize into a square wave. The more inverters you have in a row, the slower the 'clock speed' of the square wave.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#27
In reply to #25

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 9:41 AM

By the way, am I the only one who looks at threads like these, then checks out the user page of the original poster to see what other questions they have asked?

What I see usually raises a lot more questions that I would prefer not to ask out loud, primarily because I don't use that sort of vocabulary in public forums.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply Off Topic (Score 5)
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#31
In reply to #25

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 12:00 PM

With slow chips like the good old reliable TTL family of gate logic this will work fine but often unpredictably about what frequency will be achieved. This approach should be frowned upon in circuit designs today. I have many times seen one of these logic oscillator loops sitting at a logic state of 1/2 instead of oscillating with the very fast gate technologies used today. This should never be attempted inside an ASIC.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#33
In reply to #31

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 12:26 PM

I never said it was a valid design for a modern circuit.

Read through my post again, look at the tone of my words.

I was describing a lab project for first-year electronics students.

This makes a simple oscillator that the student can look at and understand, and once they know this, we can move on to more sophisticated designs, possibly using piezoelectric chips as 'frequency filters' to stabilize an oscillator at a specific frequency with little variance.

It's a good circuit for people to start with when they need to learn their basic electronics theory, like building S-R flip-flops from discrete chips. You'd never use those in a commercial or industrial application like that (and if you're going to use flip-flops, you'd more likely be using edge-triggered J-K flip-flops with Preset and Clear), but one needs to learn to crawl before they can learn to walk.

Look at the OP's profile, look at the threads he has started, and you'll understand why I am using simple examples here.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#34
In reply to #33

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 12:45 PM

I agree a logic oscillator can be a good place to start but caveats should be stated because the flaws in this circuit are not obvious. I stated them.

I remember a company I worked for tested the speed of the logic gates they got by making this loop and measuring the output frequency. (I vaguely remember three NAND gates being used.) I think it was a 74FXX series that was tested this way and it produced a nice steady 2.5 VDC instead of oscillating.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#35
In reply to #34

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 2:00 PM

"I think it was a 74FXX series that was tested this way and it produced a nice steady 2.5 VDC instead of oscillating."

Ah, that's why it didn't work, 74F is Fast-Response, if I'm reading the code right, I said to use 74LS Low-Power Shotkey. Also, three gates even in LS might not be enough to provide a good propagation delay.

If memory serves, the 74LS chips are so ubiquitous because they provide a decent response while still being effectively dirt-cheap. the other chip lines are more expensive, the 54 series are 'Military Grade,' and certified for a wider temperature range, for example, and while it is possible to make 74XX chips, they would be no cheaper than 74LS chips, and the increased power consumption would be a disincentive to use them.

Also, when making actual Integrated Circuits, the NAND gate is the easiest type to manufacture, so almost everything is made from NAND gates, Inverter - Single input NAND, AND gate - NAND with a NAND-based inverter after it, OR gate - NAND gate with NAND-based inverters on all the inputs, etc.

But we're getting away from the central point, keeping things simple for the OP. Once we know that he understands 'how an oscillator gets output without giving input signal,' then we can talk about what is a good oscillator for the project he is working on.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9197
Good Answers: 1046
#17

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/03/2015 8:10 PM

In practice, it gets started when you turn it on (apply power). From that point feedback keeps it going.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Aug 2005
Location: Hemel Hempstead, UK
Posts: 5425
Good Answers: 293
#22

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 5:28 AM

There is a good article here about CMOS oscillators

http://users.ics.forth.gr/~kateveni/120/10f/extra03_osc.pdf

It's Fairchild's Application note 118.

Here is a simple oscillator and its wave forms from the note:-

__________________
We are alone in the universe, or, we are not. Either way it's incredible... Adapted from R. Buckminster Fuller/Arthur C. Clarke
Register to Reply Score 1 for Good Answer
Power-User

Join Date: Dec 2007
Posts: 177
Good Answers: 6
#23

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 8:30 AM

in simplest form, positive feedback from output to input

Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#24
In reply to #23

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 9:09 AM

Positive feedback is how a comparator creates hysteresis. Just adding positive feedback is not enough. Positive feedback is certainly a pivotal part but far from all that's needed to be known.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#26
In reply to #24

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 9:35 AM

Yes, you also need a delay, so the signal 'chases its own tail.' but the circuitry itself often supplies that.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru

Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1676
Good Answers: 122
#39
In reply to #26

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 8:37 AM

Isn't the delay provided by the capacitor charge & discharge time?

__________________
They said; "Brain size?" I heard; "Train size?" so I said: "I'll take a small one, thank you."
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#41
In reply to #39

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 9:34 AM

If you're building one with a capacitor, then the RC time constant(s) determine delay time. I was referring to my simple TTL inverter chain example, which relies only on simple logic gates.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru

Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1676
Good Answers: 122
#46
In reply to #41

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 11:59 AM

Got it. Thanks!

__________________
They said; "Brain size?" I heard; "Train size?" so I said: "I'll take a small one, thank you."
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#42
In reply to #39

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 9:45 AM

In Randall's circuit the capacitor does provide the dominant feedback delay. In the circuit adreasler described all of the delay was just transistor switching delays.

Oh and the waveforms Randall sketched will not be exactly as drawn. The input of very first inverter will have a diode to clamp negative voltages. The charge and discharge curves will not be simple exponential curves but depending on the values of R and C this deviation maybe difficult to see.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1676
Good Answers: 122
#47
In reply to #42

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 12:00 PM

Thanks!

__________________
They said; "Brain size?" I heard; "Train size?" so I said: "I'll take a small one, thank you."
Register to Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16499
Good Answers: 662
#28

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 10:53 AM

Most logic based oscillators rely on noise (thermal) to get them started the output of one gate must be high or low (due to the design) .
Which way a gate starts is pretty much down to how the circuit happens to start during power up, various delays in the circuit and noise. Once one output goes high (or low) that transition is fed back to gate inputs which will cause the output to change... this takes a finite time. The change gets fed back and becomes another change... and that's the oscillation.

To answer part of your initial question. The DC power supply comes up slowly and that gives rise to undefined logic states and instability which will start the process as one gate goes high or low as various voltage thresholds are reached.

If you want to argue the other way and say ... "what about an instantaneously applied power supply?"

I'd argue that it will produce an edge which will propagate through the circuit similarly producing a logic output of either high or low at one output, once this is generated the oscillation continues.

Of course it may not oscillate if everything happens to come up in perfect equilibrium, but that is as likely as throwing a dozen coins in the air and them all landing balanced on their edge!

Del

__________________
health warning: These posts may contain traces of nut.
Register to Reply
Guru

Join Date: Feb 2008
Location: Large hole formally occupied by furry woodland creature.
Posts: 3385
Good Answers: 97
#29
In reply to #28

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 11:03 AM

I plug in or turn on my appliances at zero crossing. You have to be real quick.

__________________
CRTL-Z
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#30
In reply to #29

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 11:50 AM

I know I should have something witty to say about that, but I'm just drawing a blank. Did someone switch my coffee for decaf again?

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Power-User

Join Date: May 2007
Location: Hurst, Texas
Posts: 178
Good Answers: 4
#36

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/04/2015 3:51 PM

Think of a see-saw: to get started (if two people are the same weight) power has to be input to start the action. One person has to push off to start the action, then when they reach the top, the other person pushes off to continue it. When they stop pushing off, the see-saw will reach equilibrium and stop moving. (Power off)

The board and the weight of the two people are analogous to resonant circuit components and if you vary the weight and/or the length of the board, the frequency of the action changes.

Oscillators depend on LEAD AND LAG introduced by the values of the components. (Which is what coils, capacitors, and resistors introduce into the circuit.

A good book is the "Amateur Radio Handbook" put out by the ARRL. Try a used book store. Any "Hams" you know may have an old copy you can talk them out of. The basic theory hasn't changed (that I know of).

._ ._.

_... .. ._.. ._..

__________________
Bill H.
Register to Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16499
Good Answers: 662
#37

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 2:45 AM

I think we are in the realms of hobbyist here.
I don't think a hobbyist is going to be designing an ASIC (slaps head with paw).

74HC series gates (CMOS) make perfectly good oscillators for hobyist use... I used one on for the speed controller on this project.

There are many good manufacturers application notes to back up this assertion.

http://cr4.globalspec.com/blogentry/6416/DIY-Electric-Golf-Trolley

Del

__________________
health warning: These posts may contain traces of nut.
Register to Reply Score 1 for Good Answer
Guru

Join Date: Jul 2006
Location: Silicon Valley
Posts: 5356
Good Answers: 49
#38
In reply to #37

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 4:42 AM

That's funny, I usually make oscillators by placing hamsters on hotplates. Little buggers have natural rhythm when it comes to jumping.

__________________
"Perplexity is the beginning of dementia" - Professor Coriolus
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#40
In reply to #38

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 9:26 AM

Oh I KNOW Hamsters have rhythm, did you see that one KIA comercial, about their at-the-time brand new plug-in electric?

Not only can they dance, but those female hamsters look pretty good, if I may be allowed to make that comment here.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply Off Topic (Score 5)
Guru

Join Date: Feb 2008
Location: Large hole formally occupied by furry woodland creature.
Posts: 3385
Good Answers: 97
#43

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 9:49 AM

For a fairly accurate oscillator:

"Both NIST-F2 and the standard it replaces, NIST-F1, are known as cesium-based atomic fountain clocks. This means they determine the length of a second by measuring a natural vibration inside a cesium atom. Within the clock, lasers push together a ball of 10 million cesium atoms and cool them to near absolute zero (which helps reduce noise). The ball is tossed up in a 3-foot chamber, passing through a microwave beam. The microwave beam kicks some of the cesium atoms up into a higher energy state, which causes them to emit light."

From Wired.com "How the U.S. Built the World's Most Ridiculously Accurate Atomic Clock".

__________________
CRTL-Z
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#44
In reply to #43

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 11:30 AM

If my memory is correct, a version of one of these clocks was operated on a standard commercial cargo plane. The gravity field of Earth produced a measurable space/time distortion difference between the airborne clock and an identical one on the ground.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: Feb 2008
Location: Large hole formally occupied by furry woodland creature.
Posts: 3385
Good Answers: 97
#45
In reply to #44

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/05/2015 11:45 AM

The disparity is understandable, considering the effort involved in counting 10 million balls.

__________________
CRTL-Z
Register to Reply
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#49

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/07/2015 10:15 PM

Can we call oscillator as dc to ac convertor since it is producing ac signal if input is considered as Vdc.

__________________
Success is a wall made by bricks called failures.
Register to Reply
Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

Join Date: May 2007
Location: Harlow England
Posts: 16499
Good Answers: 662
#50
In reply to #49

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/08/2015 3:33 AM

You can call it what you like... it won't make change it's function!

Del

__________________
health warning: These posts may contain traces of nut.
Register to Reply
Associate

Join Date: Mar 2015
Posts: 33
Good Answers: 1
#52

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 9:25 AM

Hello,

Your input is there, in circuit, and very real. Thermal noise in the resistors, coupled with positive feedback, gain and a filter function provided by the feedback resistors and capacitors finish the job.

Cold will sometimes not allow an oscillator to start. Increasing the value of the feedback resistors will often fix this. The larger the resistor, the more noise it generates.

Register to Reply
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#53
In reply to #52

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 10:49 AM

Then how that thermal noise is a periodic one which acts as input. Since noise is not a periodic in nature.

__________________
Success is a wall made by bricks called failures.
Register to Reply
Associate

Join Date: Mar 2015
Posts: 33
Good Answers: 1
#54
In reply to #53

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 11:01 AM

The noise spectral content can be considered infinite (white noise) for the purposes of these types of filters. Given that; if you provide a filter function to the input of a high-gain stage with positive feedback from its output, the gain stage will amplify the tiny filtered input noise signal and feed the amplified result back to its input again. If you could (and you can) capture this, you would see the signal build-up in amplitude, after the circuit is energized, to the desired (?) level. The output will be sensitive to loading, if you take too much energy from the output, the feedback level will drop below what is required to keep the oscillation going or even start.

Register to Reply
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#56
In reply to #54

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 12:10 PM

That means white noise is a periodic one???

__________________
Success is a wall made by bricks called failures.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#57
In reply to #56

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 12:25 PM

No, the white noise produces the tiny imbalance that the oscillator amplifies and feeds back to itself.

Think of a metronome, those little upside-down pendulum things used to teach music students how to mark time. The energy used to run them is from a clockwork mechanism in the base, but until the arm falls to one side or the other, the clockworks can't give it the 'kick' to keep it going, in other words, there is no signal to amplify until it is started. Normally the instructor starts the metronome by hand by flicking it to the side, either side, it does not matter which. That would be 'applying an external input' to start the oscillations. If the metronome is just left to sit on its own, then it will do nothing until a stray breeze, a passing truck outside, or a butterfly flapping its wings halfway across the world upset the delicate balance of the pendulum arm and send it falling to one side or another. once the arm falls the clockworks can provide the 'kick' to keep it going. This is 'internal white noise starting the system.' ow with electronics, it is much harder to design things to balance to well without outside help, every circuit ends up with a tiny bias toward one side or another, so within microseconds after getting power, an electronic oscillator will have started 'rumbling' in white noise, then amplified that signal, feeding it back on itself until it stabilizes into the oscillator's normal output. The white noise is still there, but it's being 'drowned out' by the much larger amplified signal.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15250
Good Answers: 939
#55
In reply to #53

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/11/2015 11:21 AM

You are absolutely correct that noise is not periodic. Remember what I said about the simulator needing just a little signal to start the oscillation. An oscillator needs an "in band" trigger signal somewhere to start the process to run. Once in a very, very, very rare while a real world oscillator circuit will not get a sufficient trigger energy level to start the process of oscillation. Once they do the bandwidth of the positive feedback circuitry will sustain that oscillation.

There is a whole lot of other additional circuit theory you need to know to fully understand an oscillator. Most of this theory will come from understanding how to prevent a circuit from oscillating. This will involve the mathematics of a LaPlace transform and understanding what is meant by the poles and zeros of a transform function. Here you will find the design mantra of keeping your poles in the left hand plane. Here you will learn the distance between your poles and the j omega axis will give you the stability of your circuit. Well to make an oscillator one must break this mantra. How one breaks this mantra will determine frequencies the oscillator vibrates and how much jitter, drift, temperature stability and other attributes an circuit has oscillator.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru

Join Date: Sep 2009
Posts: 1049
Good Answers: 88
#58

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/24/2015 9:16 AM

Your "representation" of an oscillator as a black box that has no input inside or that you are not giving it any input signal is NOT correct. Actually internally an oscillator does have an input and it uses it, and the fact you may have no access to that input and its functionality does not mean that it does not exist and work. For a system to oscillate indefinitely, it is ESSENTIAL that a portion of its output after some PROPER time shifting is fed back to its input, that's the idea behind instability and tendency to oscillate. It is as simple as that. No feedback (that requires the presence and use of an input), no indefinite oscillation generation. (The reverse of course does not apply). You should start by studying a bit more fundamental concepts before trying to ask questions that mix both primitive and high level concepts that you obviously don't fully understand, and then expect to understand the answers. S.M.

__________________
Life is complex. It has a real part and an imaginary part.
Register to Reply Score 1 for Good Answer
Associate

Join Date: Mar 2015
Location: INDIA
Posts: 49
#59

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/24/2015 9:53 AM

that means the initial noise is the white noise which is not periodic, but then how we are getting a periodic waveform as output?

__________________
Success is a wall made by bricks called failures.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3688
Good Answers: 89
#60
In reply to #59

Re: How an Oscillator Gets Output Without Giving Input Signal?

03/24/2015 10:23 AM

Please look back to Post #57 in this thread for the answer.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Register to Reply 60 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

adreasler (11); Bill H. (1); Brave Sir Robin (1); Dave G (1); Del the cat (3); Ed Watts (1); jack of all trades (3); jhotmer (2); Lokeshloki (6); lrsheldon (1); lyn (3); ozzb (1); PWSlack (3); Randall (1); redfred (9); Rixter (1); SHOCKHISCAN (4); SimpleMind (1); Tornado (1); Unredundant (3); vermin (3)

Previous in Forum: Operational Technology Security Procedure   Next in Forum: EDC

Advertisement