# 5.3 Design of linear-phase fir filters by general interpolation

 Page 1 / 1
(Blank Abstract)

## Design of fir filters by general interpolation

If the desired interpolation points are not uniformly spaced between $0$ and $\pi$ then we can not use the DFT. We must take a different approach. Recall that for a Type I FIRfilter, $A()=h(M)+2\sum_{n=0}^{M-1} h(n)\cos ((M-n))$ For convenience, it is common to write this as $A()=\sum_{n=0}^{M} a(n)\cos (n)$ where $h(M)=a(0)$ and $\forall n, 1\le n\le N-1\colon h(n)=\frac{a(M-n)}{2}$ . Note that there are $M+1$ parameters. Suppose it is desired that $A()$ interpolates a set of specified values: $\forall k, 0\le k\le M\colon A({}_{k})={A}_{k}$ To obtain a Type I FIR filter satisfying these interpolation equations, one can set up a linear system of equations. $\forall k, 0\le k\le M\colon \sum_{n=0}^{M} a(n)\cos (n{}_{k})={A}_{k}$ In matrix form, we have $\begin{pmatrix}1 & \cos {}_{0} & \cos (2{}_{0}) & & \cos (M{}_{0})\\ 1 & \cos {}_{1} & \cos (2{}_{1}) & & \cos (M{}_{1})\\ \\ 1 & \cos {}_{M} & \cos (2{}_{M}) & & \cos (M{}_{M})\\ \end{pmatrix}\left(\begin{array}{c}a(0)\\ a(1)\\ \\ a(M)\end{array}\right)=\left(\begin{array}{c}A(0)\\ A(1)\\ \\ A(M)\end{array}\right)$ Once $a(n)$ is found, the filter $h(n)$ is formed as $\{h(n)\}=1/2\{a(M), a(M-1), , a(1), 2a(0), a(1), , a(M-1), a(M)\}$

## Example

In the following example, we design a length 19 Type I FIR. Then $M=9$ and we have 10 parameters. We can therefore have 10 interpolation equations. We choose:

$\forall k, {}_{k}=\{0, 0.1\pi , 0.2\pi , 0.3\pi \}0\le k\le 3\colon A({}_{k})=1$
$\forall k, {}_{k}=\{0.5\pi , 0.6\pi , 0.7\pi , 0.8\pi , 0.8\pi , 1.0\pi \}4\le k\le 9\colon A({}_{k})=0$
To solve this interpolation problem in Matlab, note that the matrix can be generated by a single multiplication of a columnvector and a row vector. This is done with the command C = cos(wk*[0:M]); where wk is a column vector containing the frequency points. To solve the linear system ofequations, we can use the Matlab backslash command.

N = 19; M = (N-1)/2;wk = [0 .1 .2 .3 .5 .6 .7 .8 .9 1]'*pi;Ak = [1 1 1 1 0 0 0 0 0 0]';C = cos(wk*[0:M]);a = C/Ak; h = (1/2)*[a([M:-1:1]+1); 2*a([0]+1); a(1:M]+1)];[A,w] = firamp(h,1);plot(w/pi,A,wk/pi,Ak,'o') title('A(\omega)')xlabel('\omega/\pi')

The general interpolation problem is much more flexible than the uniform interpolation problem that the DFT solves. Forexample, by leaving a gap between the pass-band and stop-band as in this example, the ripple near the band edge is reduced(but the transition between the pass- and stop-bands is not as sharp). The general interpolation problem also arises as asubproblem in the design of optimal minimax (or Chebyshev) FIR filters.

## Linear-phase fir filters: pros and cons

FIR digital filters have several desirable properties.

• They can have exactly linear phase.
• They can not be unstable.
• There are several very effective methods for designing linear-phase FIR digital filters.
On the other hand,
• Linear-phase filters can have long delay between input and output.
• If the phase need not be linear, then IIR filters can be more efficient.

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
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Got questions? Join the online conversation and get instant answers!