This is the time it takes for the signal to transition from 20% of its final value to 80% of its final value. The second definition is the 20–80 rise time. It can be read directly off the time domain plot of a waveform. This is usually the default meaning of rise time. The 10–90 rise time is how long it takes for the signal to transition from 10% of its final value to 90% of its final value.
There are two popular definitions of rise time. The rise time is related to how long it takes for the signal to transition from a low value to a high value. Equation 2-1įor example, a clock with a period of 10 nsec will have a clock frequency of 1/10 nsec = 0.1 GHz or 100 MHz. The clock frequency, F clock, or how many cycles per second the clock goes through, is the inverse of the clock period, T clock. The clock period is the time interval to repeat one clock cycle, usually measured in nanoseconds (nsec). The fall time is typically slightly shorter than the rise time and sometimes creates more noise. But what do we really mean? What is the time domain? What are the features that are special about the time domain that make it useful? These are surprisingly difficult questions to answer because they seem so obvious and we rarely think about what we really mean by the time domain.įigure 2-1 Typical clock waveform showing the clock period and the 10–90 rise time for a 1-GHz clock. However, as we will see, they are intimately related.įinally, we'll apply this concept of bandwidth to interconnects, models, and measurements. The first is a time-domain term and the second a frequency-domain term. We will apply what we learn to relate two important quantities: rise time and bandwidth.
#Bipolar square wave harmonics how to
We will find that while we may generally be more familiar with the time domain, the frequency domain can provide valuable insight to understand and master many signal-integrity effects such as impedance, lossy lines, the power-distribution network, measurements, and models.Īfter introducing the two domains, we will look at how to translate between the two for some special cases. In particular we'll use the time domain and the frequency domain. The different perspectives we will use to look at signals are called domains. The quickest path to the answer may not be the most obvious path.
We will find that there are multiple ways of looking at a signal, each providing a different perspective. Learn the sonic signature of this edgy recipe of harmonics, and you’ll learn to spot distortion when things are going wrong, and you’ll have an aural starting point for when you choose to distort on purpose.Signal and Power Integrity - Simplified, 2nd Edition This specific recipe of odd harmonics will create a square wave that is perfectly square, if you have a bandwidth that goes to, um, infinity.Īs the bandwidth narrows, as it rolls of the high frequencies, the wave becomes less square. In all cases, we carefully follow the equation above, choosing the right frequency components, each with exactly the right amplitude needed to make a square wave. Including twenty-five harmonic components, closer still. With five harmonics, a crude square wave form takes shape.Ĭrunching thirteen harmonics gets us closer. It’s not yet square, because we need more harmonics. Three harmonics – those three spikes on the frequency domain plot – add up to a bat-signal sort of wave form in the time domain. It shows the amplitude as a function of frequency. The image on the right is the all-important frequency representation of the same wave. The image on the left is a plot in the time domain – the amplitude versus time waveform you see in your digital audio workstation. Let a computer crunch the numbers and we can begin to graph the square wave. Let’s build a square wave with a fundamental frequency of 100 Hz. We’ll set the peak amplitude to 1 volt, and step through the first three harmonics by letting n = 1, 2, and then 3. Where Apeak is the peak amplitude of the square wave, ƒis frequency in Hertz, and t is time in seconds. What are the harmonics in a square wave? Glad you asked. This suggests one way to learn to hear distortion: listen for the sound of the associated harmonic structure. Hard clip a sine wave and it becomes square-ish, very square-ish.
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