First order digital filter

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omid2006

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Hello friends
I found a unknown digital low pass filter in a sample code but I can't adapt it's formula with common filters like IIR because it's like a IIR filter with negative coefficient. it's like feedback filter but feedback filter is a highpass in ordinary and this filter is low pass. I'll write it's formula and I appreciate if anyone can help.

Code: 
out[n]+=(in[n]-out[n-1])*500*Ts

and Ts is the sampling frequency thus execution rate of filter.
 

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3 different results from the following :

out[n]+=(in[n]-out[n-1])*500*Ts

OR

out[n]=out[n] +(in[n]-out[n-1])*500*Ts
 

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The second equation is the first equation, post #1, just the += expanded.

So yes, not feasible, except by, as MATLAB complained, adding in all paths a unit delay.
Which I did and got it to solve. But then, and here is where I am over my head, I think it
just causes group delay, but magnitude response still accurate......not sure.

The above is why I recommended to OP to do a recursive solution in Excel to look at samples
generated, and hence plots.

Makes me wonder if there is a typo here from OP or his source.
 

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danadakk said:
The second equation is the first equation, post #1, just the += expanded.
Click to expand...
No, it makes no sense to write u[n] on RHS of the assignment, must be u[n-1]. There's one unit delay created by performing the assignment periodically.

Step response is monotical.
 

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