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The story of Knee Frequency. Ruxin Xie 11.05.2013. Why it’s called Knee frequency. Knee Frequency?. Knee Frequency?. Knee Frequency?. Definition of the Knee frequency. Note: Pulse shape hardly matters K = 0.35 is typically used K = 0.5 for conservative approximation
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The story of Knee Frequency Ruxin Xie 11.05.2013
Why it’s called Knee frequency Knee Frequency? Knee Frequency? Knee Frequency?
Definition of the Knee frequency • Note: • Pulse shape hardly matters • K = 0.35 is typically used • K = 0.5 for conservative approximation • Imprecise measurement • Advantage: • Simply defined based on rise time • Easy benchmark of frequency effect
How to calculate the Knee frequency Amplitude (Linear scale) 90% Amplitude (Linear scale) 50% 10% FFT Time E(t) = A0exp() E(𝜔) = A1exp() Set E(𝜔) = 0.5, 𝜔 = Since 𝜎 = Tr10%-90% /1.69, 𝜔 = 2𝜋f f = 0.32/ Tr10%-90% Set E(t) = 10%, t10% = 𝜎 E(t) = 90%, t90% = 𝜎 Tr10%-90% = | t90% -t10% | = 1.69𝜎 Frequency (Hz)
Simulation Results Assume Square wave signal, Tr10%-90% = 1ns, T = 10ns, Duty Cycle = 50% fknee = 0.32/ Tr10%-90% = 0.32/1ns = 0.32 GHz
Simulation Results K = 0.27 K = 0.32 K = 0.5
Thank you! Questions?