Fir filters with multiplexed inputs suitable for use in reconfigurable adaptive equalizers

A method of sharing arithmetic operators in a feed forward equalizer comprising an N-tap finite impulse response filter for filtering a signal having a first sampling rate, where N is an integer greater than 1, the method comprising the steps of:

• providing a first set of multiplexers for receiving real and imaginary portions of a first set of complex tap signals and a second set of multiplexers for receiving real and imaginary portions of a first set of complex tap coefficients;
• operating the first and second sets of multiplexers at a rate at least twice the sampling rate, to selectively output the real and the imaginary portions of the first set of complex tap signals and the real and the imaginary portions of the first set of complex tap coefficients;
• providing a first set of arithmetic operators;
• and
• operating the first set of arithmetic operators to generate the real portion resulting from a complex multiplication of the real and imaginary portions of the first set of complex tap signals and the real and imaginary portions of the complex tap coefficients output by the first and second sets of multiplexers each time the first and second sets of multiplexers selectively output the real and imaginary portions of the first set of complex tap signals and the real and imaginary portions of the first set of complex tap coefficients.

A method of sharing arithmetic operators in a feedback equalizer circuit comprising a real N-tap finite impulse response filter for filtering a signal, where N is an integer greater than 3, the method comprising the steps of:

• providing a first multiplexer for receiving a first and second tap coefficient;
• providing a second multiplexer for receiving a first and second tap signal;
• providing a third multiplexer for receiving a third and forth tap signal;
• providing a fourth multiplexer for receiving a third and fourth tap coefficient;
• providing a first and second multiplier and a first summer coupled to the first and second multipliers;
• operating the first and second multiplexers to output the first tap coefficient and first tap signal, respectively;
• operating the third and fourth multiplexers to output the third tap signal and third tap coefficient, respectively;
• operating the first and second multipliers to multiply the first tap coefficient with the first tap signal and the third tap coefficient with the third tap signal, to generate first and third tap signal outputs, respectively;
• and
• operating the first summer to sum the first and third tap signal outputs.

A real 4-tap finite impulse response filter for generating a filter output signal as a function of a first through fourth tap signal and a first through fourth tap coefficient, the 4-tap finite impulse response filter comprising:

• a first multiplexer for receiving and selectively outputting a first and a second tap coefficient;
• a second multiplexer for receiving and selectively outputting a first and a second tap signal;
• a first multiplier coupled to the first and second multiplexers for multiplying the first tap signal with the first tap coefficient and the second tap signal with the second tap coefficient;
• a third multiplexer for receiving a third and a fourth tap signal;
• a fourth multiplexer for receiving a third and a fourth tap coefficient;
• a second multiplier coupled to the third and the fourth multiplexers for multiplying the third tap signals with the third tap coefficient and the fourth tap signal with the fourth tap coefficient;
• and
• a summer coupled to the first and second multiplexers.