How to create a test bench waveform for the working of band pass and low pass filter

Hi,

I created a band pass filter and low pass filter through sptool in matlab and imported the co-efficients into workspace

Now I need to write a testbench for the working of these filters.

Can anyone suggest something about this

Thanks in advance

Answer 1

[Honglei Chen]

Hi Vivek,

What is the purpose of the test bench? If you purpose is to look at the filter response, then in my opinion it is better to examine the filter response. Say you have the filter coefficients b and a, then you can do

>> fvtool(b,a)

to look at the response.

If you really want to pass the data, you can use randn to generate some white noise data and then run it through the filter, e.g.,

>> x = randn(1024,1);
>> y = filter(b,a,x);

HTH

[Jim]

Hi,

Thanks for ur reply

I used this command where b,a given as the filter co-efficients of bandpass filter imported into workspace from sptool.

I got the array size for Y as 1024*1 double

Actually what happend by using this command

Thanks in advance

[Jim]

Hi,

Thanks for ur reply

I need to create a test bench for the verification the specified amplitude- and phase transfer functions of the calculated IIR lowpass and bandpass filters

My friend used this function to create bandpass filter

Z=filterIIR2t(Mxr,Num1,Den1); %to create band pass filter

where Num1,Den1 are filter co-efficients and defined this

function as which is used as test bench

function y = filterIIR2t(x,Num,Den)

c=Num;

d=Den;

sz=size(Num);

k=sz(2)-1;

reg=zeros(k,1);

ind=1;

for v=x

y(ind)=v*c(1)+reg(1);

reg(1:k-1)=(v*c(2:k)-y(ind)*d(2:k))'+reg(2:k);

reg(k)=v*c(k+1)-y(ind)*d(k+1);

ind=ind+1;

end;

Can u explain me what this function will do

Thanks in advance

[Honglei Chen]

Hi Vivek,

If I'm not mistaken, the test bench coded you showed performs the filtering. This is exactly what filter() does in my example. X is your input and Y is your output, i.e., the filtered signal.

[Wayne King]

Hi Vivek, from what I can tell by the name of your colleague's function, it should be implementing a direct-form II transposed structure. The built-in MATLAB filter() which Honglei has recommended also uses a direct-form II transposed structure.

[Jim]

Hi,

Thanks for ur reply

So,without using my friends testbench function filterIIR2t(x,Num,Den) we can directly use inbuilt function

filter(b,a,x)

But when I am using this function filter(b,a,x) I am not getting any response

Can u suggest me something about this

Thanks in advance

[Wayne King]

Did you design your filter as a filter object, or as coefficients.

filter() also works with filter objects, so if you have a filter object, use

filter(Hd,x) where Hd is your object

if you have coefficients, then b should be Num and a should be Den

filter(Num,Den,x)