Filter for 2B1Q signals
AssigneeIndustrial Technology Research Institute
InventorsYung-Chow Peng, Ta-Cheng Hsiung
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Abstract
A filter is disclosed for filtering 2B1Q coded symbols from the set (-3, -1, +1, +3) to obtain convolutions of the form ##EQU1## without any multiplications by three. The convolution is obtained by using two accumulators to separately accumulate coefficients a.sub.j where the corresponding symbol has a magnitude one and where the corresponding symbol has a magnitude three.
Claims9
A filter method for evaluating convolutions of the form ##EQU8## where a.sub.j is a coefficient having a sign s(a.sub.j) and magnitude m(a.sub.j) and q(n-j) is a 2B1Q symbol having a first bit q.sub.o in indicating the sign of q(n-j) and a second bit q.sub.1 indicating the magnitude of q(n-j), said filter method comprising the steps of:
- (a) clearing a value stored in a first accumulator and a second accumulator,
- (b) determining P.sub.j =q.sub.o XOR s(a.sub.j), where q.sub.o is the sign bit of the coefficient q(n-j),
- (c) determining whether an addition/subtraction unit performs an addition or substraction operation based on said bit P.sub.j, and
- (d) in response to P.sub.j, adding or subtracting m(a.sub.j) from said value stored in said first accumulator if q.sub.1 has a first value and adding or subtracting m(a.sub.j) from said value stored in said second accumulator if q.sub.1 has a second value, where q.sub.1 is the magnitude bit q(n-j),
- (e) repeating said steps (b) to (d) for each of said coefficients a.sub.j.
A filter for evaluating convolutions of the form ##EQU9## where a.sub.j is a coefficient having a sign s(a.sub.j) and a magnitude m(a.sub.j) and q (n-j) is a symbol having a first bit q.sub.0 indicating the sign of the symbol and a second bit q.sub.1 indicating the magnitude of the symbol, said filter comprising
- an addition/subtraction unit,
- a first accumulator connected to receive an output of said addition/subtraction unit, and
- a circuit connected to determine whether said addition/subtraction unit performs an addition operation or a subtraction operation, said circuit being connected to output a signal to said addition/subtraction unit, for each coefficient a.sub.j :
- said circuit is connected to determine in response to s(a.sub.j) and the sign bit q.sub.o of the corresponding coefficient q(n-j) whether said addition/subtraction unit performs an addition or subtraction for each coefficient a.sub.j,
- said addition/subtraction unit is connected to add or subtract m(a.sub.j) to a value stored in said first accumulator if the magnitude bit q.sub.1 of q(n-j) is a first value.
- said addition/subtraction unit is connected to add or subtract m(a.sub.j) to a value stored in said second accumulator if the magnitude bit q.sub.1 of q(n-j) is a second value, and
- said addition/subtraction unit is connected to add a final value stored in said second accumulator to a final value stored in said first accumulator a plurality of times to obtain said final output value y(n).
Dependencies are inferred from the claim text.