# 0.3 Filtering of noise - 2

 Page 1 / 1
this module considers the effect on power spectrum of noise after ffiltering

## Psd after filtering:

The relation between a ,b and c and $\phi$ which describe the noise components can be seen to be identical with that between X,Y and R and $\theta$ .

Hence pdf of c is Rayleigh and that of $\theta$ is uniform.

$f\left({c}_{k}\right)=\frac{{c}_{k}}{{P}_{k}}{e}^{-{c}_{k}^{2}/{2P}_{k}}{c}_{k}0$ , $f\left({\theta }_{k}\right)=\frac{1}{2\pi }-\pi \le {\theta }_{k}\le \pi$

Let a spectral component of noise be the input to a filter whose transfer function at frequency $\mathrm{k\Delta f}$ is

$H\left(\mathrm{k\Delta f}\right)=\mid H\left(\mathrm{k\Delta f}\right)\mid {e}^{\mathrm{j\varphi k}}=\mid H\left(\mathrm{k\Delta f}\right)\mid \angle {\varphi }_{k}$

The output spectral component of noise is

${n}_{\text{ko}}\left(t\right)=\mid H\left(\mathrm{k\Delta f}\right)\mid {a}_{k}\text{cos}\left(2\pi k\Delta \text{ft}+{\varphi }_{k}\right)+\mid H\left(\mathrm{k\Delta f}\right)\mid {b}_{k}\text{sin}\left(2\pi k\Delta \text{ft}+{\varphi }_{k}\right)$

The power associated with the input component is

${P}_{\text{ki}}=\frac{\overline{{a}_{k}^{2}}+\overline{{b}_{k}^{2}}}{2}$

As $\mid H\left(\mathrm{k\Delta f}\right)\mid$ is a deterministic function, $\overline{{\left[\mid H\left(\mathrm{k\Delta f}\right)\mid {a}_{k}\right]}^{2}}={\mid H\left(\mathrm{k\Delta f}\right)\mid }^{2}\overline{{a}_{k}^{2}}$

Similarly for ${b}_{k}$ , and thus the power associated with noise output is

${P}_{\text{ko}}={\mid H\left(\mathrm{k\Delta f}\right)\mid }^{2}\frac{\overline{{a}_{k}^{2}}+\overline{{b}_{k}^{2}}}{2}$

And the power spectral densities are related by

${G}_{\text{no}}\left(f\right)={\mid H\left(f\right)\mid }^{2}{G}_{\text{ni}}\left(f\right)$

Where the $\mathrm{k\Delta f}$ has been replaced by $f$ as a continuous variable as $\mathrm{\Delta f}$ tends to 0.

## Superposition of noises:

Noise can be represented as superposition of (orthogonal) harmonics of $\mathrm{\Delta f}$ therefore total power is the result of superposition of component powers.

Consider Two processes ${n}_{1}$ and ${n}_{2}$ with overlapping spectral components.

Power of the sum of ${n}_{1}$ and ${n}_{2}$ will be ${p}_{1}+{p}_{2}+2E\left[{n}_{1}{n}_{2}\right]$ and since ${n}_{1}$ and ${n}_{2}$ are uncorrelated, the last term = 0.

Then these noises also obey the superposition of powers rule.

## Mixing of noise with a sinusoid

If ${k}^{\text{th}}$ component of noise is mixed with a sinusoid

$\begin{array}{}{n}_{k}\left(t\right)\text{cos}{2\pi f}_{o}t=\frac{{a}_{k}}{2}\text{cos}2\pi \left(\mathrm{k\Delta f}+{f}_{o}\right)t+\frac{{b}_{k}}{2}\text{sin}2\pi \left(\mathrm{k\Delta f}+{f}_{o}\right)t\\ +\frac{{a}_{k}}{2}\text{cos}2\pi \left(\mathrm{k\Delta f}-{f}_{o}\right)t+\frac{{b}_{k}}{2}\text{sin}2\pi \left(\mathrm{k\Delta f}+{f}_{o}\right)t\end{array}$

Sum and difference frequency noise spectral components with 1/2 amplitude are generated and

${G}_{n}\left(f+{f}_{o}\right)={G}_{n}\left(f-{f}_{o}\right)=\frac{{G}_{n}\left(f\right)}{4}$

Considering power spectral components at $\mathrm{k\Delta f}$ and $\mathrm{l\Delta f}$ , let the mixing frequency be ${f}_{0}=\left(k+l\right)\mathrm{\Delta f}$ . This will generate 2 difference frequency components at the same frequency: $\mathrm{p\Delta f}={f}_{0}-\mathrm{k\Delta f}=\mathrm{l\Delta f}-{f}_{0}$

Then difference frequency components are

${n}_{\mathrm{p1}}\left(t\right)=\frac{{a}_{k}}{2}\text{cos}2\pi p\Delta \text{ft}-\frac{{b}_{k}}{2}\text{sin}2\pi p\Delta \text{ft}$
${n}_{\mathrm{p2}}\left(t\right)=\frac{{a}_{l}}{2}\text{cos}2\pi p\Delta \text{ft}+\frac{{b}_{l}}{2}\text{sin}2\pi p\Delta \text{ft}$

But as $\overline{{a}_{k}{a}_{l}}=\overline{{a}_{k}{b}_{l}}=\overline{{b}_{k}{a}_{l}}=\overline{{b}_{k}{b}_{l}}=0$ , We find $E\left[{n}_{\mathrm{p1}}\left(t\right){n}_{\mathrm{p2}}\left(t\right)\right]=0$

and $E\left\{{\left[{n}_{\mathrm{p1}}\left(t\right)+{n}_{\mathrm{p2}}\left(t\right)\right]}^{2}\right\}=E\left\{{\left[{n}_{\mathrm{p1}}\left(t\right)\right]}^{2}\right\}+E\left\{{\left[{n}_{\mathrm{p2}}\left(t\right)\right]}^{2}\right\}$

Thus superposition of power applies even after shifting due to mixing.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Got questions? Join the online conversation and get instant answers!