- By Eric Bogatin
- Jul 22, 2009
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.