Active vs Passive Filter: Difference and Comparison

Key Takeaways

1. Active filters use active components like operational amplifiers to shape the frequency response, while passive filters use only passive components such as resistors, capacitors, and inductors.
2. Active filters can provide gain and improve the signal-to-noise ratio, whereas passive filters can only attenuate the signal.
3. Active filters require external power sources for operation, while passive filters do not need additional power.

What is an Active Filter?

An active filter is an analog circuit that implements an electronic filter with an active component like an amplifier. Adding amplifiers to a filter design can improve its cost, performance, and predictability. In an active filter, an amplifier prevents the load impedance of the next stage from affecting the filter characteristics.

With an active filter, complex poles and zeros are achieved without using bulky or expensive inductors. In active filter circuits, one parameter can be adjusted without affecting the others, including the response shape and Q (quality factor).

The active filters are electronic filters consisting of operational amplifiers and passive filters containing elements like resistors and capacitors. There are a few limitations to using active filters. There is no consideration for the finite bandwidth of amplifiers in basic filter design equations.

Due to their limited bandwidth, active devices are not practical at high frequencies. In addition to consuming power, amplifiers produce noise. When there is no DC path for bias current to reach the amplifier elements, certain circuit topologies may not be practical. The amplifier stages limit the power handling capability.

Active filters are of different kinds based on the bands of frequencies they allow or reject.

• Active Low Pass Filter
• Active High Pass Filter
• Active Band Pass Filter
• Active Band Stop Filter

What is a Passive Filter?

Passive filters consist of capacitors, inductors, and resistors tuned to resonate at a specific frequency or a range of frequencies. Passive filters are used in power systems to reduce voltage distortion and harmonic currents that appear in sensitive areas of the system.

The passive filters function by displaying various impedance values at the resonance frequency. The harmonic frequency blocked has a high impedance when a filter is connected in series.

Although connecting filters in a series configuration is an option, more common forms are parallel connections. Such a shunt configuration provides reactive power that can improve the power factor while simultaneously diverting harmonic currents to the ground.

Thus, capacitive at the fundamental frequency is the intended property of passive shunt filters. Passive filters are frequently used to supply the needed frequencies and properties to circuits containing amplifiers, oscillators, and power supply circuits.

There are different kinds of passive filters given below.

1. Low Pass Filter
2. High Pass Filter
3. Band Pass Filter
4. Band Stop Filter

Difference Between Active and Passive Filter

Active and passive filters are types of electronic filters that are used to filter specific frequencies from signals. Both active and passive filters are different in their design and their functions. There are many differences between active and passive filters, but the key difference is.

1. The active filter uses transistors and operational amplifiers for frequency filtration. In contrast, passive filters use resistance, inductors, and capacitors for signal generation.
2. Active filters depend on an external power supply, whereas passive filters do not require any power; they operate on signal input.

Comparison Between Active and Passive Filter

Parameters	Active Filter	Passive Filter
Definition	An active filter is an analog circuit that implements an electronic filter with an active component like an amplifier.	Passive filters consist of capacitors, inductors, and resistors tuned to resonate at a specific frequency or a range of frequencies.
Efficiency	Active filter is efficient and transmits frequencies at a sharper rate.	A passive filter is less efficient and transmits frequencies at a slower rate.
Complexity	Active filters are more complex.	Passive filters are simpler and less complex.
Sensitivity	More sensitive.	Less sensitive.
Cost	Active filters are high-cost or expensive.	Passive filters are cost-effective and less expensive.

References

1. Elwakil, A.S. and Maundy, B.J., 2014. Single transistor active filters: What is possible and what is not. IEEE Transactions on Circuits and Systems I: Regular Papers, 61(9), pp.2517-2524.
2. Busarello, T.D.C., Pomilio, J.A. and Simoes, M.G., 2016. Passive filter aided by shunt compensators based on the conservative power theory. IEEE Transactions on Industry Applications, 52(4), pp.3340-3347.