Different Types of Active Filters and Its Applications
Published: 2023-07-05 07:40:35

## What is Active Filters

[Active filters](https://www.avaq.com/category/integrated-circuits-ics/active-filter) are electronic circuits that use active components, typically operational amplifiers (op-amps), to achieve the desired filtering characteristics. Unlike passive filters that rely solely on passive components (resistors, capacitors, and inductors), active filters incorporate active devices to enhance their performance and provide additional functionalities.


The primary active component used in active filters is the operational amplifier. Op-amps are integrated circuits that have high gain, high input impedance, low output impedance, and are capable of amplifying signals. By utilizing op-amps in active filter designs, various filter responses can be achieved, such as low-pass, high-pass, band-pass, and band-stop.

## Types of Active Filters

**Butterworth Filter:
**
- Provides a maximally flat frequency response in the passband.
- Features a smooth roll-off without ripples in the passband or stopband.
- Suitable for applications where a flat response is important, such as audio systems and data acquisition.

**Chebyshev Filter:
**
- Offers a steeper roll-off than the Butterworth filter but introduces ripples in either the passband or the stopband (or both).
- Can be designed as either a Chebyshev Type I filter with ripples in the passband or a Chebyshev Type II filter with ripples in the stopband.
- Used in applications where a sharper roll-off is required, such as wireless communication systems and signal processing.

**Bessel Filter:
**

- Provides a nearly linear phase response, which preserves the shape of the filtered waveform.
- Exhibits a slower roll-off compared to Butterworth or Chebyshev filters.
- Suitable for applications where maintaining phase linearity is crucial, such as audio crossover networks and medical instrumentation.

**Elliptic Filter (Cauer Filter):
**

- Offers the steepest roll-off among all the filter types but introduces ripples in both the passband and the stopband.
- Allows for precise control over the filter response and can achieve high selectivity.
- Used in applications where stringent filtering requirements are necessary, such as telecommunications and radar systems.

**Sallen-Key Filter:
**

- A popular active filter topology that uses op-amps and resistors/capacitors to implement various filter responses.
- Simple to design and provides low-pass, high-pass, band-pass, and band-stop filtering capabilities.
- Widely used in audio systems, tone control circuits, and active equalizers.

**Multiple Feedback (MFB) Filter:
**

- Another common active filter configuration that utilizes op-amps and capacitors/resistors to achieve different filter responses.
- Suitable for implementing low-pass, high-pass, and band-pass filters.
- Often used in anti-aliasing filters, active audio filters, and instrumentation amplifiers.

## Active Filters Application

- Audio systems (equalizers, crossover networks)
- Instrumentation and measurement equipment
- Communication systems (wireless transceivers, base stations)
- Power electronics (power quality improvement, EMI reduction)
- Biomedical instrumentation (ECG, EEG)
- Control systems
- Signal processing (audio effects, speech recognition)
- RF systems (frequency selection, channel filtering)