Passive Filter Circuits

Explain what a band-pass filter is, and how it differs from either a low-pass or a high-pass filter circuit. Also, explain what a band-stop filter is, and draw Bode plots representative of both band-pass and band-stop filter types.

A common way of representing complex electronic systems is the block diagram, where specific functional sections of a system are outlined as squares or rectangles, each with a certain purpose and each having input(s) and output(s). For an example, here is a block diagram of an analog (“Cathode Ray”) oscilloscope, or CRO:

Block diagrams may also be helpful in representing and understanding filter circuits. Consider these symbols, for instance:

Which of these represents a low-pass filter, and which represents a high-pass filter? Explain your reasoning.

Also, identify the new filter functions created by the compounding of low- and high-pass filter “blocks”:

What kind of filtering action (high-pass, low-pass, band-pass, band-stop) does this resonant circuit provide?