Knee Frequency
CHAPTER 11.8 Periodic Waves and Fourier Transform
In analyzing high speed digital signals, many factors depend upon the frequency of the signal. This includes, for example, the value of the impedance of the capacitance, signal path loss. Knee frequency is an estimate of the highest frequency content of the signal. It depends upon the rise time of the signal. If the rise time is smaller, the highest frequency content will have higher frequency. If t denotes the 10% to 90% rise time of a signal, then an estimate for the highest frequency content of the signal or the knee frequency is given by
We will buttress the understanding of the frequency spectrum by learning about the Fourier Transform. You may skip the content below and come back and read it in your leisure time. But just keep in mind that a faster rising edge signal means it has higher frequency component.
PCB Design for High Speed Next - Fourier Transform