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Describes different filter types. Lowpass, highpass, bandpass, bandstop, allpass and notch filter.

So what is a filter? In general a filter is a device that discriminates, according to one or more attributes at its input, what passes through it.One example is the colour filter which absorbs light at certain wavelengths. Here we shall describe frequency-selective filters. It is called freqency-selectivebecause it discriminates among the various frequency compononents of its input. By filter design we can create filters that pass signals with frequencycomponents in some bands, and attenuates signals with content in other frequency bands.

It is customary to classify filters according to their frequency domain charachteristics. In the following we will take a look at: lowpass, highpass, bandpass, bandstop, allpassand notch filters. (All of the filters shown are discrete-time)

Ideal filter types


Attenuates frequencies above cutoff frequency, letting frequencies below cutoff( f c ) through, see .

An ideal lowpass filter.


Highpass filters stops low frequencies, letting higher frequencies through, see .

An ideal highpass filter.


Letting through only frequencies in a certain range, see .

An ideal bandpass filter.


Stopping frequencies in a certain range, see .

An ideal bandstop filter.


Letting all frequencies through, see see .

An ideal allpass filter.
Does this imply that the allpass filter is useless? The answer is no, because it may have effect on the signals phase. A filteris allpass if H 2 f 1 , f . The allpass filter finds further applications as building blocks for many higher order filters.

Other filter types

Notch filter

The notch filter recognized by its perfect nulls in the frequency response,see .

Notch filter.
Notch filters have many applications. One of them is in recording systems, where the notch filter serve to removethe power-line frequency 50 Hz and its harmonics(100 Hz, 150 Hz,...). Some audio equalisers include a notch filter.

Matlab files

idealFilters.m , notchFilter.m

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Information and signal theory. OpenStax CNX. Aug 03, 2006 Download for free at http://legacy.cnx.org/content/col10211/1.19
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