![]() The FFT of an ideal sine wave in the time domain yields just one sinusoidal frequency component, the sine wave’s frequency. If the sample rate is 100 GHz, the highest frequency component that can be calculated with an FFT is 50 GHz. The highest frequency bin in the spectrum is ½ the sample rate of the measured or simulated data in the time domain.For example, if the average in the time domain is 0.5 V, the amplitude of the 0 Hz frequency component is also 0.5 V. The average value of V(t) in the time domain, over the acquisition window, is the amplitude of the DC component, the 0 Hz frequency bin, in the frequency domain spectrum.frequency resolution) is 1/1 usec = 1 MHz. ![]() If the total time window is 1 usec, the frequency interval between each bin (i.e. The first frequency component above DC and the interval between frequency bins, frequency resolution, are related to the total acquisition time over which V(t) data is simulated or recorded. The acquisition window is a time interval which repeats. The spectrum is calculated by sampling the waveform over a finite span with an acquisition window.These apply to an FFT of a waveform whether the waveform is simulated or measured. There are three features in the time domain waveform that translate directly into features in the frequency domain. Only the magnitude of the complex amplitude is generally displayed, but there is an associated phase as well. This changes a time domain V(t) waveform into a frequency domain spectrum consisting of a complex sinusoidal amplitude in each spectral frequency bin, A(f). For digital signals, since their frequency range starts at DC, bandwidth refers to the highest sinusoidal frequency component of the signal that is “significant.” The ambiguity is in the definition of “significant.” Just looking at the spectral components of a time domain signal in the frequency domain is not enough to answer the question “what is significant?” Time Domain Waveform Representation in the Frequency DomainĪ time domain signal is generally transformed into the frequency domain with a Fast Fourier Transform (FFT), which is a fast matrix solution of a Discrete Fourier Transform (DFT). When applied to RF signals, this is generally the range of frequency components in the spectrum about the carrier frequency and is often categorized as narrow band or wide band. Bandwidth is, fundamentally, the frequency range of a signal’s “significant” spectral components. While the term bandwidth is used when referring to the frequency components of a signal, it has an ambiguous definition that must be clarified before it can be applied to help gain insight into its relationship with rise time and slew rate. 1 Two waveforms have the same rise time but a factor of 5 different slew rate. 224 Gb/s Per Lane: Options and Challengesįig.
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