We propose a new design method for FIR digital filters with arbitrary passband by using interpolation techniques. Interpolated FIR (IFIR) filters have a sparse impulse response with every Lth sample being nonzero and can be implemented by replacing each delay of an original filter with L delays. We call L the interpolation ratio. L is an integer. Then the frequency band is reduced to 1/L. To implement a desired passband, the IFIR filter requires only 1/L multipliers of the direct form FIR digital filter. Using this method it is possible to implement a narrowband filter with fewer than 30 percent multipliers of the direct form, and a wideband lowpass filter with fewer than 40 percent multipliers.
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