Composite finite impulse response digital filter

Claim 1

A composite finite impulse response digital filter including a cascade arrangement of sub-filters, and a first latch for storing data input into a first one of said sub-filters, each of said sub-filters comprising: a barrel shifter which in the case of the first sub-filter in the cascade shifts data output from said first latch and in the case of each other sub-filter in the cascade shifts data output from the preceding sub-filter in the cascade, wherein each barrel shifter shifts the respective data input thereto to a selected one of the least significant bit side and the most significant bit side of the data over a number of shifts corresponding to a first control signal; first adding means having first and second input terminals for adding data input into the first input terminal from the respective barrel shifter and data input into the second input terminal; and second storing means for temporarily storing data output from said first adding means and outputting said data thus stored to the second input terminal of said first adding means and also, in the case of all but the last sub-filter in the cascade, to an input terminal of the next sub-filter in the cascade; wherein an output terminal of a preceding sub-filter is connected to an input terminal of the next sub-filter to have said sub-filters connected in series; and said digital filter including a multiplying and adding means for multiplying data output from each of a selected number of said sub-filters by a multiplier factor corresponding to a second control signal and adding the thus multiplied data to produce added data which in turn are output as output data of said cascade.