What is active and passive filters and What are the types of passive and active filters

What is a filter

A filter is circuitry that can be used to solve the power quality-related problems, a filter can be considered as a reactive network which can freely pass the desired band of frequency while it suppresses all the other bands.

What is active filters

Active filters can be considered as the combination of passive and active components, and they need an outside power source. Operational filters are used in active filters. These can have high-quality factors and can achieve resonance without the use of inductors, the upper-frequency limit of the active filters is limited by the bandwidth of the amplifiers.

What is passive filters

Passive filters have passive components, they do not use any external power supply nor have any active components such as transistors or battery. The simplest passive filters, are RC and RL filters they only have one reactive element.

What are the difference between active and passive filters

  • Passive filters consume the energy but no power gain is available, while active filters have a power gain
  • Active filter needs an external power supply, while the passive filters operate only on the signal input
  • Passive filters use inductors and active filters doesn’t
  • Passive filters don’t have any frequency limitations while active filters have limitations due to active elements
  • Passive filters can withstand large currents and they have better stability
  • Passive filters are cheaper than active filters

What are the types of passive and active filters

SAW filter

A surface acoustic wave filter is a passive filter, in which the electrical input signal is converted to an acoustic wave by the use of an interdigital transducer on a piezoelectric substrate called quartz. The transducer has metal electrodes that can launch and receive the waves so that the electrical signal is converted to an acoustic wave and then back to an electrical signal. The most common types of saw filters are bandpass filters, which are widely used in radio systems.

What is a sine wave filter

Sine wave filters are low pass frequency filters, it is a passive filter that converts the rectangular PWM output signal of motor drives into a smooth sine wave voltage with low residual ripple. Sine wave filters can be installed between a VFD power source and the motor. This will smooth the VFD pulse width modulated square wave signal and converts it into a perfect sinusoidal power waveform, This combination will help the motor to run at a continuously adjustable speed. Running the motor without sine wave filters can cause several problems.

What is a power line filter

A power line filter is a type of passive component which can create an electronic filter to deliver appropriate frequency characteristics to electrical circuits. Power line filters connect the electronic device with an external line to reduce conducted frequencies like radio frequencies or electromagnetic interference between the equipment and the connecting power line, and this will prevent any degradation in circuit performance. A power filter can reduce electromagnetic interference in the power line of any equipment.

What is a signal filter

A signal filter is a passive filter, it will only pass specified frequency and rejects other electrical signals, mostly for noise reduction. Signal filtering is used in eddy current testing to eliminate unwanted frequencies from the receiver signal.

What is a Chebyshev filter

Chebyshev filter is also known as an equal ripple filter, it is an analog or digital filter which has a stepper roll off and has more pass-band and stop-band ripple than Butterworth filters. It has the property that it can reduce the error between the idealized and the actual filter characteristic over the range of the filter but with ripples in the passband.

What is a Butterworth filter

It is a type of active filter, it is a type of signal processing filter which is designed to have a frequency response as flat as possible in the pass-band. These filters are also known as maximally flat magnitude filter. These filters are the most commonly used digital filters in motion analysis and in audio circuits.

What is a Bessel filter

Bessel filter is an active filter, it gives a constant propagation delay across the input frequency spectrum. Applying a square wave to the input of a Bessel filter will yield a square wave on the output with no overshoot. Other types of filters will delay different frequencies with different amounts. Bessel filters are used in audio cross over systems.

What is an elliptical filter

An elliptical filter is an active filter which is used in many RF applications where a very fast transition between the pass-band and stop-band frequencies are needed. It produces the fastest transition of any type of filter, but it also exhibits gain ripple in both passband and stopband.

What are the applications of active filters

  • It is used in the communication system to suppress noise and to isolate the communication signal from various channels to improve the unique message signal from a modulated signal.
  • It can be used to limit the analog signal bandwidth before altering them to digital signals
  • It is used in instrumentation systems, to choose a required frequency apparatus and detach unwanted ones.
  • These filters are used in biomedical instruments to interface sensors with diagnostic equipment and data logging.