Analog filter

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Electronic filters are called analog filters or analog filters if they process the signals continuously in terms of time and amplitude. They are used either to form signals in the desired sense or to determine which frequencies are represented ( signal analysis ).

Analog filters are the opposite of digital filters . This lies in the implementation: Analog filters are built with passive electronic components such as capacitors , coils , resistors or actively with operational amplifiers .


Analog filters dampen or amplify (like their digital counterparts) certain signal components or oscillations in a mixture of frequencies . An example of attenuation is a notch filter that suppresses signal components of a certain frequency. A frequent application is the suppression of the 50 Hz mains frequency when these signal components interfere with signal transmissions. A band-stop filter attenuates signals from an entire frequency range, a band-pass filter allows signals from a frequency range to pass and amplifies the signal if it is dimensioned accordingly. A low pass filter transmits (amplifies) signals below a cutoff frequency. A high pass filter transmits (amplifies) signals above a cutoff frequency.


Important types of analog filters are:

With electromechanical filters, electrical energy is converted into mechanical energy or vice versa during the filtering process.


Passive analog filters can be implemented in the form of different topologies , with the two-port representation with complex impedances Z and complex admittances Y being common, particularly in electrical circuit technology . With appropriate model design, this type of filter display can also be applied to other analog filters, such as for mechanical systems.

In the following tables some common passive analog filter topologies are summarized, as they can also be found in the field of two-port theory. The subdivision is made into ground- asymmetrical and ground- symmetrical forms.

Unbalanced grounding shapes
L filter T filter Π filter
Image Filter L Half-section.svg
Image filter T Section.svg
Image filter Pi Section.svg
Chain ladder
Image Filter Ladder Network (Unbalanced) .svg
Ground symmetrical shapes
C filter H filter Box filter
Image Filter C Half-section.svg
Image Filter H Section.svg
Image Filter Box Section.svg
Chain ladder
Image Filter Ladder Network (Balanced) .svg
X filter ( lattice filter , mid-T lead) X-filter (lattice filter, mid-Ab-derivative)
Image filter X Section.svg
Image filter X Section (Pi-Derived) .svg

Advantages and disadvantages

Advantages over digital filters

  • low latency
  • they represent time-continuous systems, so there is no limitation by the sampling rate as with time-discrete systems.
  • for purely passive filters:
    • Filter properties largely independent of the strength of the input signal
    • can be implemented for all conceivable services by choosing suitable components
    • no additional operating voltages required for active components


  • poorer reproducibility of the filter properties due to the tolerances of the processed components
  • Depending on the requirements, an adjustment or calibration is necessary .
  • less flexible to use
  • Higher filter orders require a large number of components.

Basically, there are numerous applications where the use of analog filters is unavoidable, since they can be built with correspondingly high-performance by choosing the appropriate components. Examples are harmonic filters in high-voltage networks.

When converting time-continuous signals into time-discrete signals or vice versa in the context of digital signal processing , time-continuous (analog) filters are generally used to avoid aliasing .


Individual evidence

  1. ^ Rüdiger Ballas, Günther Pfeifer, Roland Werthschützky: Electromechanical systems of microtechnology and mechatronics . 2nd Edition. Springer, 2009, ISBN 978-3-540-89320-2 .

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