On-line arithmetic modules for recursive digital filters

An online multiply-add (MA) module is designed for implementing second-order direct-form IIR filters. The MA module is implemented in a 0.7- mu m HCMOS gate array technology. An array of MA modules is developed to perform the second-order recursive computations at 128 Msamples/s with two levels of scattered lookahead. A conventional (bit-parallel) design using similar lookahead is implemented in the same technology. The 104-Msample/s conventional design implements a carry-free recursive loop and uses radix-4 recoding to reduce the number of partial products. The online array has a sampling rate higher than the conventional implementation for 12 or more bits.