Active Filter vs. Passive Filter — What's the Difference?

Active Filters are electronic filters that use active components like transistors and operational amplifiers, along with resistors and capacitors, to filter a signal. They require an external power source for their operation. Passive Filters, in contrast, do not use active components and are built using only resistors, capacitors, and inductors. They do not require an external power source and operate passively on the input signal.

One key advantage of Active Filters is their ability to provide signal gain, meaning they can amplify the filtered signal. This is not possible with Passive Filters, which can only attenuate the signal. Active Filters are also better at providing higher selectivity and can maintain constant bandwidth over a range of frequencies.

In terms of design and complexity, Active Filters are generally more complex and costly than Passive Filters. However, they offer greater flexibility in tuning and modifying the filter characteristics. Passive Filters, being simpler, are easier to design and more cost-effective but offer less flexibility.

Active Filters are less susceptible to load impedance variations, which means their performance is more consistent regardless of the connected load. Conversely, the performance of Passive Filters can be greatly affected by load variations, leading to a change in their filtering characteristics.

Finally, in terms of frequency range, Active Filters are typically used for lower frequency applications, as they become unstable at high frequencies. Passive Filters, on the other hand, are suitable for both low and high-frequency applications, making them versatile in a broader range of scenarios.