If the "oscillator" has only two states (which it does because it is a logic gate), and has some hysteresis (ditto) it needs 180' phase shift from input to output. Which is why we use inverters.

A single RC is all it needs, to provide ANY time delay between the output changing state and the input following it.

"Extraordinary claims require extraordinary proof." Somehow every reference on oscillation theory states the phase shift needs be a multiple of 360 degrees.

If the entire world is wrong and you are right... start by checking your work.

The problem Ernie is that you're talking about a linear oscillator and everybody else is talking about an inverting-gate relaxation oscillator. Or as you called it, a multivibrator. So most of what you've written is irrelevant. And frankly, your condescending attitude serves only to make you look like a wise guy. (Not to be confused with "wise man.")

multivibrator != oscillator

I'm sorry, but that is simply not true. A multivibrator is a type of oscillator. Look up "electronic oscillator" in Wikipedia. Not all oscillators are linear.

 

I personally would never make an oscillator out of a gate and RC network if no Schmitt trigger was present. Because without the Schmitt trigger input there is no guarantee of oscillation. The gate could simply remain stable at some quiescent point somewhere between the high and low logic levels.

Just because a data sheet calls the device a logic gate doesn't mean it will behave as one when used unconventionally.

Come to think of it, decades ago I built a circuit that incorporated the following astable multivibrator:

I had used this circuit numerous times before, but for some reason this time it refused to oscillate. Upon further thought, I realized that should both transistors become saturated at the same time, no oscillation would occur.

I haven't used the circuit since.

 

There's an increasing amount of "robust discussion" on AAC - some have noted this with concern, particularly when it gets personal.

Perhaps in deference to the [long absent] OP, this thread should be allowed to sink into the abyss.

 

A multivibrator is a type of oscillator.

I suppose then that a bistable (or monostable) multivibrator is an oscillator? News to me...

 

I suppose then that a bistable (or monostable) multivibrator is an oscillator? News to me...

Well there is lots you don't know. Why just today I searched "electronic oscillator" on Wikipedia and even I learned that there are "Oscillators designed to produce a high-power AC output from a DC supply." Who would have thought that? I wonder what phase shift they use?

Of course, the article came with the full Wikipedia seal of quality:

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.

 

A multivibrator is a type of oscillator.

I suppose then that a bistable (or monostable) multivibrator is an oscillator? News to me...

People say, "Obama is the President of the United States."

I suppose then that my neighbor Jack Obama is the POTUS? News to me...


Moral: Taking in context what people say is a great way to understand them correctly. We *were* talking specifically about an astable multivibrator (being formed from a inverter gate).

 

Taking in context what people say is a great way to understand them correctly. We *were* talking specifically about an astable multivibrator (being formed from a inverter gate).

Perhaps you should go back and re-read the very first post of this thread where the OP (who owns the thread and thus defines the context) defined the thread topic as "one inverter oscillator."

I understand the hijack attempts to obscure some incorrect information put forth. I thus correct and attempt to bump the thread back to the topic at hand.

If the OP ever returns here, of course he is free to redirect the topic.

 

Perhaps you should go back and re-read the very first post of this thread where the OP (who owns the thread and thus defines the context) defined the thread topic as "one inverter oscillator."

A "one-inverter oscillator" is an astable multivibrator. Just as a 74123 or 74221, when connected to oscillate, are astable multivibrators. Same thing with an oscillating 555. Every experienced electronics designer knows this.

Just because the OP didn't use the phrase "astable multivibrator" doesn't mean that's not what he was talking about.


BTW, I just found the following thread of designers discussing ways to build an astable multivibrator:

http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=80699

Note the one guy saying you could have six astable multivibrators with a single 74HC14 inverter chip.

 

Moral: Taking in context what people say is a great way to understand them correctly. We *were* talking specifically about an astable multivibrator (being formed from a inverter gate).

I did not take what you wrote out of context:

I'm sorry, but that is simply not true. A multivibrator is a type of oscillator.

This statement is simply backwards! It is ok to say that an oscillator can be a type of multivibrator, but it is not correct to say a multivibrator is a type of oscillator.

 

This statement is simply backwards! It is ok to say that an oscillator can be a type of multivibrator, but it is not correct to say a multivibrator is a type of oscillator.

What??? That's like it's OK to say that a beverage can be a type of beer, but it is not correct to say beer is a type of beverage.
Multivibrator is a subclass of oscillator, not the other way around.

 

The late Jim Williams seemed to have no concern with interchangeable use of either term. See in particular AN-12 from Linear Technology stable.

 

The late Jim Williams seemed to have no concern with interchangeable use of either term. See in particular AN-12 from Linear Technology stable.

An RC multivibrator is an oscillator.
A Colpitts oscillator is not a multivibrator.
A Wien bridge oscillator is not a multivibrator.
Jim Williams may have (correctly) called a multivibrator an oscillator, but I don't think he called a crystal oscillator a multivibrator.

 

No argument on that point Ron.

 

What??? That's like it's OK to say that a beverage can be a type of beer, but it is not correct to say beer is a type of beverage.
Multivibrator is a subclass of oscillator, not the other way around.

I think your beer analogy is just a bit off. A picture is worth a thousand words:

I was correct when I said "an oscillator can be a type of multivibrator." I was also correct to say "it is not correct to say a multivibrator is a type of oscillator."

But I was wrong to say "This statement is simply backwards!", since neither multivibrators and oscillators are subsets of eachother.

Likewise, Ron, it is incorrect to say that "Multivibrator is a subclass of oscillator."

 

You are right, of course. I had completely forgotten about the other types of multivibrators.

 

No problem.

Actually, does anyone really use the (archaic) word "multivibrator" any more? I think words like "one-shot", "flip-flop", and "oscillator" are far more common these days.

BTW, I just learned today from Wikipedia (it must be true!) that:

The name "multivibrator" was initially applied to the free-running oscillator version of the circuit because its output waveform was rich in harmonics.

Yes, I suppose that makes quite a bit of sense as a square wave tends to have lots of harmonics...

Edit: Oh, and by that definition, I presume you could call any free-running oscillator that has significant harmonic distortion a multivibrator

 

No problem.

Actually, does anyone really use the (archaic) word "multivibrator" any more? I think words like "one-shot", "flip-flop", and "oscillator" are far more common these days.

BTW, I just learned today from Wikipedia (it must be true!) that:



Yes, I suppose that makes quite a bit of sense as a square wave tends to have lots of harmonics...

Edit: Oh, and by that definition, I presume you could call any free-running oscillator that has significant harmonic distortion a multivibrator

Joeyd999 & Ron,

Thanks for those interesting insights. I found the Venn diagram particularly informative.

Notwithstanding the fact that the thread is well and truly hijacked, the informative aspects came to prominence when the personal jibes of some earlier posts were discarded and the the quest for a consensus became the goal.

On the matter of whether something is an oscillator or a multivibrator seems to me something that is hard to strictly define. We seem to be able to say that something is or is not an an oscillator for instance but what is it that actually makes it an oscillator an oscillator? Some aspect or aspects of its physical behaviour? Is it defined by output purity? Perhaps not. Is it defined by functionality?

There is an story from the Buddhist tradition in which a king and esteemed monk discuss the point as to what is a chariot? The king had arrived in a chariot to learn from the wisdom of the monk. In the end the king agreed with the monk there was no such thing as "a chariot".

 

It has been my experience that when a design engineer uses the term "multivibrator" without a qualifier he is invariably referring to the astable form. The Jim Williams application note is good example of this. The original statement made by Ron is another.

In the trade, a monostable multivibrator is usually called a one-shot and a bistable multivibrator is usually called a flip-flop. Maybe that's the reason people say simply "multivibrator" when referring to the oscillating one.

The inventors of the oscillating multivibrator didn't call it an "astable multivibrator"... they called it a multivibrator. And they were the ones who coined the term. The monostable and bistable forms were later derived from that original multivibrator. This may be another reason people say "multivibrator" when referring to the oscillating one.

(Source: http://mysite.du.edu/~etuttle/electron/elect36.htm )

Given that this is the popular and widely accepted usage of the term "multivibrator" (outside of academia), Ron was right in stating, "An RC multivibrator is an oscillator." (Even if he now thinks he was wrong.)

 

"As a physician, you of all people should appreciate the danger of re-opening old wounds." ~James T. Kirk

 

"As a physician, you of all people should appreciate the danger of re-opening old wounds." ~James T. Kirk

"Undoubtedly there is a perverse nature within me." ~ t_n_k