Filter with multipliers operating in ones complement arithmetic
A finite impulse response filter, including a plurality of taps arranged to receive and process a sequence of input data samples so as to generate a filter output. Each tap consists of a multiplier operating in one's complement arithmetic, the multiplier being coupled to multiply a respective input sample from the sequence by a respective equalization coefficient, and an adder, which sums an output from the multiplier. The taps are arranged in sequence so that the input sample to each of the taps, except to a first tap in the sequence, is delayed relative to a preceding tap in the sequence. The filter also includes an adjustment-accumulator coupled to receive the filter output and responsive thereto to generate an adjustment that is adapted to correct the filter output to a twos complement result, and an adjustment-adder which sums the adjustment and the filter output to generate a final output.
1. A finite impulse response filter, comprising:
a plurality of taps arranged to receive and process a sequence of input data samples so as to generate a filter output, each tap comprising:
a multiplier operating in ones complement arithmetic, the multiplier being coupled to multiply a respective input sample from the sequence by a respective equalization coefficient; and
an adder, which sums an output from the multiplier, the taps being arranged in sequence so that the input sample to each of the taps, except to a first tap in the sequence, is delayed relative to a preceding tap in the sequence;
an adjustment-accumulator coupled to receive the filter output and responsive thereto to generate an adjustment that is adapted to correct the filter output to a twos complement result; and
an adjustment-adder which sums the adjustment and the filter output to generate a final output.
2. A filter according to claim 1 , wherein each of the respective equalization coefficients are adaptive in response to an error signal input to the filter.
3. A filter according to claim 1 , and comprising a sign-determining component which determines a sign and an absolute value of each of the input data samples.
4. A filter according to claim 3 , wherein if the sign is negative the adjustment-accumulator adds the absolute value to the filter output, and if the sign is positive, the adjustment-accumulator subtracts the absolute value from the filter output.
5. A filter according to claim 1 , wherein the plurality of taps are arranged in an architecture chosen from a direct-form architecture, a transpose-form architecture, and a hybrid-form architecture.
6. A method for filtering a signal, comprising:
receiving and processing a sequence of input data samples in a plurality of taps so as to generate a filter output, each tap comprising:
a multiplier operating in ones complement arithmetic, the multiplier being coupled to multiply a respective input sample from the sequence by a respective equalization coefficient; and
an adder, which sums an output from the multiplier, the taps being arranged in sequence so that the input sample to each of the taps, except to a first tap in the sequence, is delayed relative to a preceding tap in the sequence;
receiving the filter output and responsive thereto generating an adjustment that is adapted to correct the filter output to a twos complement result; and
summing the adjustment and the filter output to generate a final output.
7. A method according to claim 6 , wherein each of the respective equalization coefficients is adaptive in response to an error signal input to the filter.
8. A method according to claim 6 , and comprising a determining a sign and an absolute value of each of the input data samples.
9. A method according to claim 8 , and comprising adding the absolute value to the filter output if the sign is negative, and subtracting the absolute value from the filter output if the sign is positive.
10. A method according to claim 6 , and comprising arranging the plurality of taps in an architecture chosen from a direct-form architecture, a transpose-form architecture, and a hybrid-form architecture.