How to design FIR filter with matematical equation?

hi, 
i'm very new with DSP FIR.
i need to make a Bandpass filter with FIR design. first, i use the AM
signal for the input, then i want to get the information signal by
filtering the AM signal.
The problem is to get the value of transfer function of the FIR filter, i
need a mathematical equation, 
i don't know where to start and what equation or theory to use?!
can you give me an equation to start?
or an example to design FIR filter?
this is for my thesis, and i'm using the DSK TMS320C54...
please give me some input...thanks...



_____________________________________
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Is it already listed at http://dsprelated.com/employers.php ?

On May 23, 7:11 am, "c1910" <c_19...@hotmail.com> wrote:
> hi,
> i'm very new with DSP FIR.
> i need to make a Bandpass filter with FIR design. first, i use the AM
> signal for the input, then i want to get the information signal by
> filtering the AM signal.
> The problem is to get the value of transfer function of the FIR filter, i
> need a mathematical equation,
> i don't know where to start and what equation or theory to use?!
> can you give me an equation to start?
> or an example to design FIR filter?
> this is for my thesis, and i'm using the DSK TMS320C54...
> please give me some input...thanks...
>

To add to Clay's suggestion, in general there are very few cases
where there is a closed-form, algebraic rational solution to the
design of an FIR filter.

There are several things that you can try, these are called
"Chebyshev filter", "Butterworth filter", etc.  It is possible to
use frequency translation to get a passband filter.  Realize
that the ideal lowpass/bandpass/highpass filter does not
admit a rational, algebraic solution.  The term Chebyshev
refers to the polynomial approximation by the same name.

However, one major discovery in the 70s was that it is possible
to cast the design problem as an optimization, which turn out
that it can be done as a linear programming problem.  This is
what is today called the Remez exchange algorithm, Parks-
McClellan, etc.

Hope that helps,
Julius