High-pass fllters

Chapter 8.3 High-pass fllters

Lessons In Electric Circuits Volume II – AC Book
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Lessons In Electric Circuits Volume II – AC Book

  • 194CHAPTER 8. FILTERSlow enough impedance to short out any noise. Greater capacitance will do a better job at filteringnoise, but size and economics limit decoupling capacitors to meager values.• REVIEW:• A low-pass filter allows for easy passage of low-frequency signals from source to load, anddifficult passage of high-frequency signals.• Inductive low-pass filters insert an inductor in series with the load; capacitive low-pass filtersinsert a resistor in series and a capacitor in parallel with the load. The former filter designtries to “block” the unwanted frequency signal while the latter tries to short it out.• The cutoff frequency for a low-pass filter is that frequency at which the output (load) voltageequals 70.7% of the input (source) voltage. Above the cutoff frequency, the output voltage islower than 70.7% of the input, and vice versa.8.3High-pass filtersA high-pass filter’s task is just the opposite of a low-pass filter: to offer easy passage of a high-frequency signal and difficult passage to a low-frequency signal. As one might expect, the inductive(Figure 204,8.10) and capacitive (Figure 203,8.8) versions of the high-pass filter are just the opposite of theirrespective low-pass filter designs:1002V11 VC10.5 µFRload1 kΩFigure 8.8: Capacitive high-pass filter.The capacitor’s impedance (Figure 203,8.8) increases with decreasing frequency. (Figure 204,8.9) Thishigh impedance in series tends to block low-frequency signals from getting to load.capacitive highpass filterv1 1 0 ac 1 sinc1 1 2 0.5urload 2 0 1k.ac lin 20 1 200.plot ac v(2).end