loop gain in multivibrators

Thread Starter

vigi04

Joined Sep 9, 2009
12
i am not understanding the concept of loop gain in a bistable multivibrator. can anyone explain it. how do u visualize loop gain in a bistable multivibrator?:confused:
 

Wendy

Joined Mar 24, 2008
21,840
I don't think there is such a thing. By definition, it is a digital circuit, it's trigger levels are defined by the logic family used to make it.

Another name for bistable multivibrator is a set/reset flip flop.

Here are a couple of examples.

 

Thread Starter

vigi04

Joined Sep 9, 2009
12
this is based on the working of the circuit.
at some places they say tat loop gain has to be more for the working of a bistable multivibrator, at others, they say that it has to less.
which is the right sentence and why???
 

Wendy

Joined Mar 24, 2008
21,840
Show the source. Like I said, I do not believe there is such a thing as loop gain. When talking about digital circuits gain is not a factor. It is a 1, or a 0.
 

Thread Starter

vigi04

Joined Sep 9, 2009
12
i dont have the ebook, but it is mentioned in 'pulse and digital circuits' by millman and taub under the topic ' bistable multivibrators'
 

Wendy

Joined Mar 24, 2008
21,840
There are simple logics where a pure 1 and 0 can be a problem, such as diode logic. It works, but there are losses because there are no active components. With IC's this doesn't exist. The main thing for any logic family is to hit a "pure" 1 or 0 for the input, generally this does take some gain, but very little. The one thing a logic family should never do is easily operate in the linear region.

One the basic 1 or 0 requirement is met, it no longer matters, especially with bistable circuits. It sounds like you're text book is approaching it from the perspective of analog gain.

Just for laughs I typed the term loop gain in Wikipedia, here is what I got...

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

There the concept deals with the feedback loops used in amplifiers and other physical processes that use feedback loops.

I can see where such a concept might apply for a multivibrator of any sort. In the world of digital though, it is harder to apply. I'll step aside and see if anyone has better input.
 

Thread Starter

vigi04

Joined Sep 9, 2009
12
can some one please help me, i'm not able to understand this concept of loop gain in a bistable multivibrator. wen its above 1, wat happens and how?? and the same for below 1.
 

BillB3857

Joined Feb 28, 2009
2,493
Wouldn't the loop gain be a determining factor in rise/fall time of a particular device?? True, it would be internal to the device, but none the less it requires gain to perform the switching.
 
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