What is an passive filter?

Question

In electronics, what is a passive filter and could anyone please give me examples of passive filter configuration.. Thanks alot..

Answer 1

It's possibly easier to answer by saying what it is not!

The opposite, an active filter has amplifying components, that is, the POWER from a source other than the original signal is employed.

Active filters therefore require one or more three-terminal devices so as to combine the power of the original signal with the external power.

Active and passive filters are able to increase amplitude or current or voltage.  Only active filters can do both.  Active and passive filters are able to phase-shift by arbitrary amounts but in passive filters there is a significant energy loss every time (as signified by the Q-factor of a filter).

Active filters can make oscillators; passive filters cannot.

Other contributors have mentioned the basic components of a passive filter.. resistors, capacitors and inductors.  Transformers (mutually coupled inductors) are also valuable passive filter components, especially in RF circuits.

Pi, T and ladder networks are some of the best known passive formats. A ladder is a repeated combination of both and is  electrically balanced (i.e there is no explicit reference voltage). These may be used to make high-pass, low pass, bandpass, and bandstop filters.  The latter two are very difficult to make well with steep characteristics ('steep' referring to the appearance of a graph of power vs frequency).

In the commonly used sense, passive filters are not 'electronic', they are electrical.  Electronic circuits are usually understood to be active by way of the use of semiconductors.

Answer 2

A filter that contains only passive or non amplifying components.

hope that helps!

Answer 3

a passive filter is a combination of Rs, Cs, and Ls arranged such that it acts as a frequency discriminator, that is, passes some frequencies and rejects others.

wikipedia:

A passive filter is a kind of electronic filter that is made only from passive elements -- in contrast to an active filter, it does not require an external power source (beyond the signal). Since most filters are linear, in most cases, passive filters are composed of just the four basic linear elements -- resistors, capacitors, inductors, and transformers. More complex passive filters may involve nonlinear elements, or more complex linear elements, such as transmission lines.

Television signal splitter consisting of a passive hi-pass filter (left) and a passive low-pass filter (right). The antenna is connected to the s***w terminals to the left of center.

A passive filter has several advantages over an active filter:

Guaranteed stability

Passive filters scale better to large signals (tens of amps, hundreds of volts), where active devices are often impractical

No power consumption (aside from possibly taking some power out of the signal)

Inexpensive

For linear filters, generally, more linear than filters including active (and therefore non-linear) elements

They are commonly used in speaker crossover design (due to the moderately large voltages and currents, and the lack of easy access to power), filters in power distribution networks (due to the large voltages and currents), power supply bypassing (due to low cost, and in some cases, power requirements), as well as a variety of discrete and home brew circuits (for low-cost and simplicity). Passive filters are less common in integrated circuit design, where active devices are comparatively inexpensive compared to resistors and capacitors, and inductors are prohibitively expensive.