# signal waveform

Discussion in 'General Electronics Chat' started by @hacker, Nov 30, 2014.

1. ### @hacker Thread Starter New Member

Nov 30, 2014
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While reading circuits i developed this doubt that why always the(input/output) signal wave forms are shown as in the form of pulse,triangular,sinewave but never in the form of a straight line (like DC current).Why so??

2. ### crutschow Expert

Mar 14, 2008
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It's not "always" but most circuits are designed for AC since we are usually interested in processing signal information and, by definition, to carry information the signal must be AC.
But there are some circuits, like DC coupled op amp circuits, that will respond to a DC signal level. An example use of such circuits would be in a DC power supply.

3. ### @hacker Thread Starter New Member

Nov 30, 2014
10
0
Okay Crutschow,but on searching about this on web i found that mostly analog signals are represented in this type.So I want to ask u whether this has any relation with this above question?

4. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Many people would not regard a straight line as a 'wave form' ........ at least, not an interesting one .

5. ### crutschow Expert

Mar 14, 2008
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I though that was answered in my post. Most analog signals are varying since most signals of interest vary.

6. ### studiot AAC Fanatic!

Nov 9, 2007
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Can you think of (or have you come across) a circuit for which the input is a straight line?

BTW I presume by a straight line you mean a constant, as opposed to a mathematical straight line, which is called a ramp function in electronics.
Ramp functions are used in various circuits.

The only type of constant function inputs I can think of would be resistive heating as in a torch circuit.
The input to the bulb would (should) be a constant voltage / current.

At AC the mains supply at the wall provides an example of a constant input, but it is so simple we don't normally bother to show it.

Last edited: Nov 30, 2014
7. ### Alec_t AAC Fanatic!

Sep 17, 2013
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If you were plotting the response of a comparator circuit having a constant reference input and a varying input you might well plot the reference input as a straight line which the varying input plot crosses.

8. ### MrChips Moderator

Oct 2, 2009
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There is a misconception as to what constitutes a valid signal. Sometimes students examine a signal on an oscilloscope and then claim "there is nothing there".

Nothing is still something. Nothing is information. A constant logic zero has as much information as a constant logic one.

A voltage signal is a time series. It is a recording of voltages over time. If each and every recording is the same voltage this will be observed on an oscilloscope as a horizontal straight line. This is still valid and useful information, but as a previous poster said, not very interesting.

Last edited: Nov 30, 2014
9. ### studiot AAC Fanatic!

Nov 9, 2007
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Unless it's the inhibit signal to Dr Stangelove's bomb.

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