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- 2.1 The Time Domain
- 2.2 Sine Waves in the Frequency Domain
- 2.3 Shorter Time to a Solution in the Frequency Domain
- 2.4 Sine Wave Features
- 2.5 The Fourier Transform
- 2.6 The Spectrum of a Repetitive Signal
- 2.7 The Spectrum of an Ideal Square Wave
- 2.8 From the Frequency Domain to the Time Domain
- 2.9 Effect of Bandwidth on Rise Time
- 2.10 Bandwidth and Rise Time
- 2.11 What Does Significant Mean?
- 2.12 Bandwidth of Real Signals
- 2.13 Bandwidth and Clock Frequency
- 2.14 Bandwidth of a Measurement
- 2.15 Bandwidth of a Model
- 2.16 Bandwidth of an Interconnect
- 2.17 The Bottom Line

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This chapter is from the book

## 2.17 The Bottom Line

- The time domain is the real world and is typically where high-speed digital performance is measured.
- The frequency domain is a mathematical construct where very specific, specialized rules apply.
- The only reason to ever leave the time domain and use the frequency domain is to get to an answer faster.
- The rise time of a digital signal is commonly measured from 10% of the final value to 90% of the final value.
- Sine waves are the only waveform that can exist in the frequency domain.
- The Fourier Transform converts a time-domain waveform into its spectrum of sine-wave-frequency components.
- The spectrum of an ideal square wave has amplitudes that drop off at a rate of 1/f.
- If the higher-frequency components are removed in the square wave, the rise time will increase.
- The bandwidth of a signal is the highest sine-wave-frequency component that is significant, compared to the same harmonics in an ideal square wave with the same repeat frequency.
- A good rule of thumb is that the bandwidth of a signal is 0.35/rise time of the signal.
- Anything that decreases the bandwidth of a signal will increase its rise time.
- The bandwidth of a measurement is the highest sine-wave frequency where the measurement has good accuracy.
- The bandwidth of a model is the highest sine-wave frequency where the predictions of the model give good agreement with the actual performance of the interconnect.
- The bandwidth of an interconnect is the highest sine-wave frequency where the performance of the interconnect still meets specifications.
- The 3-dB bandwidth of an interconnect is the highest sine-wave frequency where the attenuation of a signal is less than -3 dB.

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