From Designing High-Speed Interconnect Circuits: Advanced Signal Integrity Methods for Engineers

Frequency Domain Analysis

Though long experience with time-domain analysis has made many of us prefer that domain, there are very good reasons to also be competent in the frequency domain. The most obvious advantage is measurement capabilities. In the frequency domain, measurements can be made over a dynamic range of about 80 to over a 100 decibels. The high end of frequency available for typical network analyzers is in the range of 20 to 50 gigahertz. By comparison, the time domain reflectometer is capable of about a 30-decibel dynamic range and about 6-gigahertz equivalent frequency response.

Conversions between Frequency and Time Domains

In Chapter 2, methods to convert between frequency domain and time domain were presented. The main procedure in this conversion, is the Fourier transform and its inverse. These are usually implemented in the form of the fast Fourier transform, FFT, and its inverse, the IFFT. These are not perfect tools inasmuch as they make the presumption that the data being analyzed is actually a portion of a repetitive wave and that presumption introduces undesired artifacts. Dealing with those artifacts sometimes requires procedures that are unpalatable to purists. It was suggested that faking data could be made more palatable by assigning an alternative name completing the data set to the procedure.

In this section, applications and uses of frequency domain data will be discussed. There are some aspects of frequency domain data that are so obvious that, when you see the graphs, you will immediately recognize the utility of this data...

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Spectrum Analyzers and Signal Analyzers
Spectrum analyzers and signal analyzers display raw, unprocessed signal information such as voltage, power, period, wave shape, sidebands, and frequency. They can provide the user with a clear and precise window into the frequency spectrum.
Infrared Spectrometers
Infrared (IR) spectrometers measure the wavelength and intensity of the absorption of infrared light by a sample.
Audio Analyzers
Audio analyzers measure the noise and audio spectrum of output from an amplifier or a stereo.
Sound Level Meters and Noise Dosimeters
Sound level meters and noise dosimeters are used in sound and noise analysis. Applications include industrial safety, traffic noise studies, and scientific noise measurement.
Optical Time Domain Reflectometers (OTDR)
Optical time domain reflectometers (OTDR) measure the elapsed time and intensity of light reflected along an optical fiber. They are useful tools for locating problems in an optical network as they can compute the distance to breaks or attenuation.

Topics of Interest

Radiation Radiation tends to be more serious as frequencies increase. When circuit boards were running at speeds of tens of megahertz, finding a trace or any other structure that was as long as a...

Overview Many methods for data analysis and modeling can be formulated in the frequency domain. Frequency domain analysis has certain advantages, including physical insight in terms of frequency...

4.1 The Fast Fourier Transform (FFT) Analysis The vibration of a machine is a physical motion. Vibration transducers convert this motion into an electrical signal. The electrical signal is then...

Vector Network Analyzers (VNAs) are very flexible measuring instruments-the microwave engineer's most powerful tool. Their basic capability is to measure the S-parameters of an RF or microwave device...

Table D.1: Fourier Transform Pairs Time domain x( t) Frequency domain X( j ?) 1 1 Table D.2: Properties of the Fourier Transform Time domain Frequency domain Table D.3: Properties of the Fourier...