[moved] Continuous vs Dicrete vs Digital vs Analog signals and systems

Hello there,

My question is just a basic clarification. Are the following definitions correct?

1. Continuous Time Signals: signals that are in a continuum i.e. they are continuous in time.
2. Discrete Time Signals: signals that are defined ONLY at specific instances in time i.e. for discrete time values only.
3. Analog Signals: continuous signals whose amplitude is also continuous are called analog signals.
4. Digital Signals: discrete-time signals with discrete amplitude are called digital signals.

Also, in 3. for analog signals, is it necessary to have the amplitude to be continuous too?

Thanks

Re: Continuous vs Dicrete vs Digital vs Analog signals and systems

I think it is the way you see the things as when you say a signal is contentious in time it means it is defined at each and every time sample so how it can be then discrete in amplitude as no transition in amplitude can take place in zero time or may be I am missing some very basic point?
As it is always the time scale which defines if a signal is contentious or discrete but in the end it depends on your need and how you are seeing the things.
Why you are confused in these definitions?

Re: Continuous vs Dicrete vs Digital vs Analog signals and systems

Thanks for your reply nomigoraya! I am not confused in the definitions. I just read two to three long pages from a book about these signals. So I wanted to make sure what I deduced from the book is correct or not! Are they right?!

Thanks much

Re: Continuous vs Dicrete vs Digital vs Analog signals and systems

So it means now I am confused can you explain me a bit what could be a signal which is continuous in time and discrete in amplitude?
As I see the things in this way that there is a signal which is continuous on both axis means on time and amplitude scale and when you need to discretize it you sample it and when you sample you discretize both time and amplitude axis as you pick a time instance and then pick amplitude corresponding to that time.
So I can not at least understand a real signal which is discrete in time but continuous in amplitude so for me continuous and analog are one and same as the discrete and digital.
For sure would love to know if my understanding is not complete

Your understanding is correct.

In some literature case #2 is sometimes described as sampled signals.
Much like sampled capacitor filters or bucket-brigade analog delays.

schmitt trigger said:

Your understanding is correct.

In some literature case #2 is sometimes described as sampled signals.
Much like sampled capacitor filters or bucket-brigade analog delays.

Click to expand...

Well it would be real help for me if you can explain what is the type of signal discrete in time (sampled in time) and even then has continuous amplitude I am sure I am missing some very basic point but I think this is the concept of this forum to get some explanation about the issues

Unfortunately I am on a business trip and is difficult to provide a lengthy reply from my phone.

But please google sampled capacitor filters or go to Texas Instruments website

https://www.ti.com/lit/an/snoa572c/snoa572c.pdf

dzafar said:

4. Digital Signals: discrete-time signals with discrete amplitude are called digital signals.

Click to expand...

That is wrong. Digital signals are discontinous signals with jump discontinuity but NOT discrete.

CataM said:

That is wrong. Digital signals are discontinous signals with jump discontinuity but NOT discrete.

Click to expand...

Can you do me a favor and define all four types as I am getting really confused as I am really confused about a signal discrete in time but continuous in amplitude.
I can understand that you can have continuous time scale but can have discrete levels of amplitude and then a signal with discrete time scale and discrete amplitude but not able to visualize the signal is discrete in time scale but have continuous amplitude

The definitions of 1 to 3 are correct. Only the 4th is wrong as already said in post #8.

Definition: A discrete-time signal is mathematically represented by a sequence of values e.g. {x[k]} where "k" goes from -infinity to + infinity



The discrete signal is written like this: {x[k]}={0,0,0,...,1,1,1,1,1,0,0,0,0....}

The digital signal is written like this: f(x)=0 when -infinity<x<alpha and x>whatever, and 1 when alpha<x<whatever

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The key point to understand the difference between discrete-time signal and digital or whatever is the following:

"k" can only be an integer value (negative as well) i.e. in maths the integer values are in the Z set.

For example, if someone asks you for the sequence value of x[3.5312] it does not exist whereas if someone asks you for the value at f(3.5312) of a digital signal it could be e.g. high or low but it does exist.


A sequence can not be mathematically defined for non integer values of its independant variable "k".