ESE 121 Lecture Notes - Lecture 18: Frequency Response, Cutoff Frequency, Bode Plot
11 Apr 2017
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Document Summary
A capacitor looks like a resistor to low frequencies, becoming infinite as the frequency tends to zero. To high frequencies, the capacitor looks like a resistor, becoming negligible as the frequency tends to infinity. In the previous circuit, frequencies above the cutoff would get sent to ground, while frequencies lower than the cutoff would be allowed to pass through to the load. Here we can see the plot of such a filter. The circuit for this plot has the cutoff somewhere between 10hz and 100hz. The way that we can tell is that the plot will read -3db at the cutoff frequency and with no additional markings we can"t determine the cf more accurately. Not all filters have such a gentle slope, this filter is a single-pole filter. The value of the slope for a single-pole filter is 6db per octave which is equivalent to 20db per decade.
