Frequency domain (Basic question)

This is a very basic question but I'm confused about the way we represent a signal in frequency domain.

Let's say I have a cosine signal in time domain : v(t)=5cos(2*pi*1000*t)

In frequency domain, why do we get a graph like this?

**broken link removed**

I know that our signal has amplitude of 5 at 1k Hz, but representing our circuit that way, we don't know anything as the frequency change.

why don't we represent it like we do in time domain?

ex. v(t) : as t change we know the amplitude on y-axis
V(f) : as f change we know the amplitude on y-axis

Like this

**broken link removed**

I'm very confused because when we do a "Bodeplot" we draw the second graph(as f change we see how a circuit behave) it is also in frequency domain.

What really is a frequency domain????

Thank you so much!

Think about an impulse that occurs only on t = 1s. When you plot this in time domain, you only get a single line over the t = 1s mark. You wouldn't extend this signal since it is confined to t = 1s.

Similarly for a signal that has only a singular frequency, you do not expand it in the frequency domain. It appears as a single line over the frequency it has.

If a signal is made up of different harmonics, then there are different amplitudes for different frequencies; the amplitudes indicate which frequencies are more dominating ones in the signal.

But the last graph you drew simply implies that the signal is composed of an infinite number of frequencies, all of which have an amplitude of 5. It doesn't represent the cosine function at all.

The Frequency domain denotes the time domain only...
The frequency domain just means that every 1ms the 5V amplitude will occur.
That in time domain is same. isn't it!!
So, it is just frequency representation of the time domain signal.

What is voltage domain of a signal.. I know a signal has time and frequency domain but what is voltage domain and how is it different from time and frequency domain and also why do we need to represent a signal in time and frequency domain? In VCO based ADC is it described that the input voltage signal is converted to time domain to obtain timing information.. why do we need to convert voltage to time domain.. I wont the voltage(sin wave) itself have timing information... what is the difference??? could anyone please show me the images of the signal in all the 3 domains?

Pavithra18 said:

What is voltage domain of a signal.. I know a signal has time and frequency domain but what is voltage domain and how is it different from time and frequency domain and also why do we need to represent a signal in time and frequency domain? In VCO based ADC is it described that the input voltage signal is converted to time domain to obtain timing information.. why do we need to convert voltage to time domain.. I wont the voltage(sin wave) itself have timing information... what is the difference??? could anyone please show me the images of the signal in all the 3 domains?

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Please don't hijack someone else's thread. All posts in this thread should be related to answering the OP's question. Start your own thread if you have a question.

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spark360z said:

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I'm very confused because when we do a "Bodeplot" we draw the second graph(as f change we see how a circuit behave) it is also in frequency domain.

What really is a frequency domain????

Click to expand...

In the Frequency Domain time is not a factor. Only the amplitude of the various frequencies of a signal are plotted. If there is only one frequency, then the plot is a vertical line centered at that frequency. In a Bode Plot the voltage is plotted at different frequencies so that makes a horizontal line of amplitude (and usually also phase) versus frequency.

In the Time Domain you plot the amplitude of the signal versus time, with the amplitude consisting of all the signal frequencies summed together at any point in time, such as you see using an Oscilloscope. To get the Frequency Domain you would use a Spectrum Analyzer which separates the signal into its individual frequency components.