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Abstract

A multi-sample multi-channel digital decimator filter producing a Finite Impulse filtering Response (FIR) from 128 digital filter coefficients for 4 independent channels with a decimation ratio of 32, i.e. each from 1,024 kHz 1-bit inputs to 32 kHz multibit outputs, splits cyclically the coefficient values in 16 groups of 8, according to the coefficient positions, into 4 Read Only Memory modules (0, 1, 2, 3). The Read Only Memory modules are coupled to the 4 multipliers (MULT 0, 1, 2, 3), wherein the coefficient value is multiplied by that of the input bit, through a multiplexer (MUXI) being able to cycle through 4 distinct conditions. The 4 adder accumulators (ACC 0, 1, 2, 3) are coupled to the outputs of their respective channel multipliers. They each partially compute in parallel outputs words using one sixteenth of the coefficients and the multiplexer rotates these words, thereby enabling complete computation in 4 cycles. 4 registers (REG 00, 01, 02, 03) are associated to each adder so as to compute 4 staggered output words simultaneously for each channel. A preferred filtering response can reduce the size of the Read Only Memory modules.

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