1. ELEC 202 Circuit Analysis II
ANALOG FILTERS
ELEC 202 Circuit Analysis II

2. Definition
A frequency-selective device or circuit designed to pass signals with desired frequencies and reject or attenuate signals with unwanted frequencies
Limit the frequency spectrum of a signal to some specified band of frequencies
Applications in communications and control systems

3. Types of Filters Lowpass – passes low frequencies and
stop high frequencies
Highpass – passes high frequencies and
rejects low frequencies
Bandpass – passes frequencies within a certain band and blocks frequencies outside the band
Bandstop – passes frequencies outside a certain band and blocks frequencies within the band

4. Lowpass Filter
Highpass Filter
Bandpass Filter
Bandstop Filter

5. Passive vs. Active Filters
A passive filter consists of only passive elements (e.g., R, L, and C).
An active filter consists of active elements (e.g., transistors and op amps) in addition to passive elements. 5

6. Cutoff Frequency
The frequency at which the frequency response drops in magnitude to 70.71% (or 3dB) of its maximum value.
Or, the frequency at which the output power of the filter is half of the maximum input power  half-power frequency
Also called corner frequency or roll-off frequency
Obtained by setting the magnitude of to 6

7. Lowpass Filter Designed to pass only frequencies from dc up to
the cutoff frequency.

8. Highpass Filter Designed to pass all frequencies above its cutoff
frequency.

9. Example What type of passive filter does the following
circuit represent? Also, calculate its cutoff
frequency.

10. Example For the circuit shown, identify the type of
filter it represent by obtaining
and calculate its corner frequency.

11. Bandpass Filter Designed to pass all frequencies within a certain
Band of frequencies.

12. Bandpass Filter

13. Bandstop Filter Designed to stop all frequencies within a certain
band of frequencies.

14. Bandstop Filter

15. Narrowband vs. Wideband
Rule of thumb:
If the 3-dB bandwidth of a bandpass filter is more than twice the center frequency, the filter is said to be wideband.
Examples of narrowband filters:
Resonator, Comb filters, notch filters,
inverse comb filters 15