Time Domain Analysis vs Frequency Domain Analysis: A Guide and Comparison

January 21, 2020 Cadence PCB Solutions

Digital wave across a dark background

 

The word analysis garners both provocations of thought and represents the epitome of illumination in terms of understanding. In essence, it is the process by which we discover or obtain a greater understanding of a person, place, or thing. Moreover, it is our analysis skills that usually keeps us safe, provided we actually use it. I recall an incident where my best friend from high school failed to do his proper analysis despite seeing all of the warning signs. Exhibit  A, large dog bowl, half-full. Exhibit B, large sign, “Beware of dog.” Finally, exhibit C, front yard completely fenced.

However, despite my warnings and the multitude of highly visible warning signs, he decides to open the gate and attempt to make his quota (a fundraiser for uniforms). As I witnessed this disaster waiting to happen safely perched on my 21-speed road bike, it happened. It was like a scene from Cujo, except it seemed to be in slow motion like the Matrix. Needless to say, he was not the “One.”

I begin pedaling for dear life while I hear a few screams behind me followed by some intense growling from a Doberman. Luckily, no one was hurt, unless you count my stomach ache from all of the laughter. However, failure to use analysis tools in electronics is almost always detrimental. Take, for example, time domain analysis and frequency domain analysis; these are two such tools that can provide invaluable signal insight if properly used.

What is Time Domain Analysis?

A time domain analysis is an analysis of physical signals, mathematical functions, or time series of economic or environmental data, in reference to time. Also, in the time domain, the signal or function's value is understood for all real numbers at various separate instances in the case of discrete-time or the case of continuous-time. Furthermore, an oscilloscope is a tool commonly used to see real-world signals in the time domain.

Moreover, a time-domain graph can show how a signal changes with time, whereas a frequency-domain graph will show how much of the signal lies within each given frequency band over a range of frequencies.

In general, when an analysis uses a unit of time, such as seconds or one of its multiples (minutes or hours) as a unit of measurement, then it is in the time domain. However, whenever an analysis concerns the units like Hertz, then it is in the frequency domain.

How is Time Domain Analysis Different from Frequency Domain?

Frequency domain is an analysis of signals or mathematical functions, in reference to frequency, instead of time. As stated earlier, a time-domain graph displays the changes in a signal over a span of time, and frequency domain displays how much of the signal exists within a given frequency band concerning a range of frequencies. Also, a frequency-domain representation can include information on the phase shift that must be applied to each sinusoid to be able to recombine the frequency components to recover the original time signal.

Furthermore, you can convert a designated signal or function between the frequency and time domains with a pair of operators called transforms. Moreover, a perfect example of a transform is the Fourier transform. Which converts a time function into an integral of sine-waves of various frequencies or sum, each of which symbolizes a frequency component. The so-called spectrum of frequency components is the frequency-domain depiction of the signal. However, as the name implies, the inverse Fourier transform converts the frequency-domain function back to the time function.

Blue signal wavelengths on a vector background

Managing antenna signals or audio transmission will change the type of analysis used.

 

Nuances Between Frequency and Time Domain

Time domain analysis provides the transitory response of a system to be analyzed, and it permits a better understanding of the flow of both mechanical and electrical energies. In general, this includes wave propagation, the structural changes of a system, and electric potential generated by external excitations.

Whereas for the frequency domain, visualization tools such as a spectrum analyzer are commonly in use when visualizing electronic signals. Also, some specialized signal processing techniques make use of transforms, and this results in a joint time-frequency domain. Moreover, the instantaneous frequency is a critical link between the time domain and the frequency domain.

Will Time Domain Analysis or Frequency Domain Analysis be Used More Often?

Time domain analysis is particularly useful for circuit designs with antennas where a designer may encounter stray signals, reflections, or ground bounce signals. Time domain signal processing enables an engineer to separate extraneous signals in time from the desired signal, thereby identifying the contaminated signals. 

In general, using a frequency domain will simplify analysis mathematically for the system running it. Many prominent SPICE tools will primarily function through the frequency-domain for this relevance, efficiency, and accuracy for their analytical functions. 

Also, mathematical systems are an essential class of systems that have various practical applicational uses. Furthermore, for a mathematical system regulated by linear differential equations, it translates the depiction of a system from that of a time domain to a frequency domain. Thereby changing the differential equation to an algebraic equation, which is considerably less difficult to solve.

Seeing a system from the viewpoint of frequency will often provide an innate understanding of the measured quality that encompasses the behavior of the system. The scientific community now offers various terminology to describe such characteristic physical system behavior in reference to time-varying inputs. This includes terms like frequency response, bandwidth, phase shift, gain, and resonant frequencies, to name a few.

One of the most familiar and universal examples of frequency content in signals is perhaps audio signals, such as music. In this case, the frequency-domain analysis gives a better understanding than time domain analysis because music is tacitly based on the breaking down of intricate sounds into their separate component frequencies. 

Oscilloscope showing signal graph

An oscilloscope is an invaluable tool for detecting signals.

 

When considering a sinusoid as an audio signal, we must also consider the changes in air pressure on our ears as a function of time. In summary, from the theory of operation of musical instruments to the musical notation in use to record and discuss music itself requires the separation of the component frequencies to gain an understanding of the audio in question.

Time domain analysis and frequency domain analysis are invaluable analysis tools. The use of either methodology depends on your individual design needs. However, in many cases, it is the use of both analysis techniques that yields the most useful insight into your design requirement needs.

Whether your electronics require time domain or frequency domain analysis, with Cadence’s suite of design and analysis tools, you’ll be sure to be equipped. Before, during, and after analysis, though, you’ll still need a layout tool and Allegro is capable of providing strong collaborative mechanics to its layout editor. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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