Active and Passive filters - eclubiitk/EClub-Handbook GitHub Wiki

The filter is a circuit which changes amplitude and phase of the input signal and produces output accordingly. It filters or eliminates some frequencies and passes some frequencies. Hence it provides different attenuation to different frequencies. Based on components used in the construction of the filter there are two types of filters i.e active filter and passive filter.

Four major types of Filters

The four primary types of filters include the low-pass filter, the high-pass filter, the band-pass filter, and the notch filter (or the band-reject or band-stop filter). Note: A notch filter is a bandstop filter with a narrow bandstop bandwidth. Notch filters are used to attenuate a narrow range of frequencies.

                                          Figure 1.1: Types of Filters

1. Low Pass Filter

Allows low-frequency signals and difficult passage to high-frequency signals.

• Inductive Low-Pass Filter

                                           Figure 1.2: Low Pass Filter

• Capacitive Low-Pass Filter

                                           Figure 1.3 Capacitive Low Pass Filter

2. High Pass Filter

Offers easy passage of a high-frequency signal and difficult passage to a low-frequency signal.

• Inductive High Pass Filter

                                            Figure 1.4: Inductive High Pass Filter

• Capacitive High Pass Filter

                                            Figure 1.5: Capacitive High Pass Filter

3. Band Pass Filter

Combining the properties of low-pass and high-pass into a single filter creates a Band Pass Filter.

                                             Figure 1.6: Band Pass Filter

4. Band Stop Filter

This kind of filter passes all frequencies above and below a particular range set by the component values.

                                            Figure 1.7: Band Stop Filter

5. Passive Filter

This filter type uses passive components such as resistors (R), coils or inductors (L) and condenser or capacitors (C) in the construction of filter. Hence it is known as passive filter.

Advantages

• Cheap

• Reliable

• Easy Design

• High Efficiency

                                              Figure 1.8: Passive Filter

6. Active Filter:

This filter type uses active components such as OP-AMP (i.e. operational amplifier) in addition to Resistors (R) and Capacitors (C) in the construction of the filter. Hence it is known as active filter.

Advantages

• No resonance issues.

• It can eliminate any harmonics

• Used for voltage regulation

• Used for reactive power compensation

• It provides reliable operation

                                            Figure 1.9: Active Filter

Applications

• Radio communications: Filters enable radio receivers to only "see" the desired signal while rejecting all other signals (assuming that the other signals have different frequency content).

• DC power supplies: Filters are used to eliminate undesired high frequencies (i.e., noise) that are present on AC input lines. Additionally, filters are used on a power supply’s output to reduce ripple.

• Analog-to-digital conversion: Filters are placed in front of an ADC input to minimize aliasing.