ECE102-1 Filters Overview

Study Notes

A filter is an electronic circuit that selectively passes or amplifies specific frequencies while attenuating others.
Basic types of filters include Low-Pass, High-Pass, Band-Pass, Band-Stop, and All-Pass filters.

Passband: Range of frequencies where the output has positive gain.
Stopband: Frequencies where output is minimal or zero.
Passband Ripple: Variations in output gain within the passband.
Stopband Ripple: Variations in output in the stopband region.
Critical Frequency: The cutoff point separating passband and stopband; typically at 70.7% voltage gain or 50% power gain.
Stopband Frequency: Frequency marking the beginning of the first stopband ripple.
Transition Band: Frequency range between critical and stopband frequencies, related to filter's slope.
Roll-off: The slope of the transition region; each pole contributes -20 dB/decade to the slope.

Suppresses frequencies below a defined cutoff frequency.
Example: An HPF with a cutoff of 100 Hz can eliminate unwanted DC voltage in amplifiers.

Allows signals within a specified frequency band to pass while attenuating frequencies outside this range.
Commonly used in tuning circuits for TVs and radios.

Attenuates a specific range of frequencies, often referred to as a notch filter.
Example: Rejects signals between 50 Hz and 150 Hz.

Passes all frequencies without attenuation, affecting only the phase of the signals.
Useful for introducing phase shifts without altering amplitude.

The order indicates the complexity of a filter, represented by n (number of inductors and capacitors).
A higher order signifies a more complex filter design.

Known as the maximally flat approximation due to a flat passband with gradual roll-off at cutoff.
Roll-off Rate Formula: 20n dB/decade or 6n dB/octave.
Main drawback: Slower roll-off compared to other filter types.