Finite impulse response filter

A finite impulse response filter for finite-impulse-response-filtering input data of a predetermined impulse form, said finite impulse response filter comprising:

• first delay means for delaying said input data by L/2 steps according to a predetermined symbol rate;
• second delay means for receiving input data from the final delay step of said first delay means and delaying it by L/2 steps according to the symbol rate;
• a first ROM bank having a plurality of ROMs for storing filter state values in accordance with a predetermined number of taps;
• a second ROM bank having a plurality of ROMs for storing filter state values in accordance with said predetermined number of taps;
• a first address generator for outputting, as is, the data of (L/2)-1 delay steps of said L/2 delay steps of said first delay means as a first address for addressing one of said filter state values stored in said ROMs of said first ROM bank when an initial delay step of said first delay means outputs a data bit having a value of logic "0", and ones complementing the output data of said (L/2)-1 delay steps for output as said first address when said initial delay step of said first delay means outputs a data bit having a value of logic "1" as said first address for addressing one of said filter state values stored in said ROMs of said first ROM bank;
• a second address generator for outputting, as is, the data of (L/2)-1 delay steps of said L/2 delay steps of said second delay means as a second address for addressing one of said filter state values stored in said ROMs of said second ROM bank when a final delay step of said second delay means outputs a data bit having a value of logic "0", and ones complementing the output data of said (L/2)-1 delay steps of said second delay means for output as said second address when said final delay step of said second delay means outputs a data bit having a value of logic "1" as said second address for addressing one of said filter state values stored in said ROMs of said second ROM bank;
• a first multiplexer for sequentially multiplexing the filter state values output from said ROMs of said first ROM bank according to a clock oversampling rate/2 times as large as the symbol rate;
• a second multiplexer for sequentially multiplexing the filter state values output from said ROMs of said second ROM bank in the reverse sequence of said first multiplexer;
• a first filter state value processing means for twos complementing the filter state value output from said first multiplexer when said initial delay step of said first delay means outputs said data bit having said value of logic "0", and outputting said filter state value output from said first multiplexer when said initial delay step of said first delay means outputs said data bit having said value of logic "1";
• and
• a second filter state value processing means for twos complementing the filter state value output from said second multiplexer when said final delay step of said second delay means outputs said data bit having said value of logic "0", and outputting said filter state value output from said second multiplexer when said final delay step of said second delay means outputs said data bit having said value of logic "1".

A finite impulse response filter for finite-impulse-response-filtering input data of a predetermined impulse form, said finite impulse response filter comprising:

• first delay means comprised of a first plurality of serially coupled delays, each of said delays delaying and outputting said input data according to a first clock rate;
• second delay means comprised of a second plurality of serially coupled delays symmetric with the respective said first plurality of delays, each of said delays of said second delay means delaying and outputting the final delay output of said first delay means according to said first clock rate;
• a counter for counting a second clock rate twice said first clock rate according to a predetermined oversampling rate, outputting a first counting result as a first output signal, and outputting a second output signal indicative of a reversal of said first counting result;
• a first multiplexer for multiplexing and outputting the data output by the initial delay of said first delay means and the output of the final delay of said second delay means according to a third clock rate four times faster than said first clock rate;
• a second multiplexer for multiplexing and outputting said first and second output signals according to said third clock rate;
• a plurality of additional multiplexers for multiplexing the data output by the rest of the delays, excluding the initial delay, of said first delay means and the rest delays of said second delay means, excluding the final delay of said second delay means, which are symmetric to the rest of the delays of the first delay device, according to said third clock rate;
• a plurality of exclusive OR gates each having a first input terminal and a second input terminal, said first input terminal being supplied with said data output by said first multiplexer, said second terminal being supplied respectively with the data output by said additional multiplexer;
• a lookup table for storing filter state values in accordance with a predetermined number of taps, and outputting a filter state value accessed by an address utilizing the output of said second multiplexer and the outputs of said exclusive OR gates;
• signal processing means for twos complementing the filter state value output from said lookup table when the output of said first multiplexer has a first logic value, and outputting, as is, said filter state value output from said lookup table when the output of said first multiplexer has a second logic value;
• a register for temporarily storing the output of said signal processing means;
• and
• an adder for summing the filter state value temporarily stored by said register and the filter state value output by said signal processing means, and outputting the summed result as filter output data.

A finite impulse response filter, having a length L, for finite-impulse-response-filtering input data of a predetermined impulse form, said finite impulse response filter comprising:

• first delay means having an L/2 plurality of serially coupled delay devices, each of said delay devices delaying and outputting said input data according to a predetermined symbol rate;
• second delay means having a L/2 plurality of serially coupled delay devices symmetric with the respective to said delay devices of said first delay means, each of said delay devices of said second delay means delaying and outputting the final delay output of said first delay means according to said symbol rate;
• a counter for counting a clock two times as large as said symbol rate according to a predetermined oversampling rate, outputting a counting result as a first output signal, and outputting a second output signal indicative of a reverse of said counting result;
• a first multiplexer for multiplexing and outputting said first and second output signals according to a clock four times as large as said symbol rate;
• a second multiplexer for multiplexing and outputting the data output by the initial delay device of said first delay means and the data output by the final delay device of said second delay means according to said clock four times as large as said symbol rate;
• a plurality of additional multiplexers for multiplexing the data output by the rest of the delay devices, excluding the initial delay device, of said first delay means and the data output by the rest of the delay devices, excluding the final delay device of said second delay means, of said second delay means which are symmetric with the rest of the delay devices of the first delay means, according to said clock four times as large as said symbol rate;
• a plurality of exclusive OR gates having a first input terminal and a second input terminal, said first input teal of each of said additional multiplexers being supplied with the data output by said second multiplexer, and said second input terminal being supplied, respectively, with the data output by said plurality of additional multiplexers;
• a ROM bank comprised of a plurality of ROMs for storing filter state values in accordance with a predetermined number of taps, and outputting the filter state values of the respective ROMs accessed by an address comprised of the outputs of said plurality of exclusive OR gates;
• means for multiplexing and outputting said filter state values output from said respective ROMs of said ROM bank in response to the output of said first multiplexer;
• signal processing means for outputting the filter state value output from said means for multiplexing, as is, when said output of said second multiplexer has a first logic value, and for twos complementing said filter state value when said ouput of said second multiplexer has a second logic value;
• a register for temporarily storing the output of said signal processing means;
• and
• an adder for summing the filter state value temporarily stored by said register and the filter state value processed by said signal processing means, and outputting the result as filter output data.

A filtering method for a finite impulse response filter having a filter length L and comprised of at least first and second ROM banks for storing filter state values in accordance with a predetermined number of taps, said method comprising the steps of:

• delaying input data of a predetermined impulse form using first and second delay lines;
• generating first and second addresses from the data delayed by said first and second delay lines, respectively;
• outputting a filter state value stored in said first ROM bank in response to said first address;
• outputting a filter state value stored in said second ROM bank in response to said second address;
• multiplexing as first output filter data, said filter state values output by said first ROM bank in response to a first clock having an oversampling rate/2 times as large as said symbol rate;
• multiplexing as second output filter data, said filter state values output by said second ROM bank in response to second clock having a reverse sequence of said first clock;
• generating filter output data by adding the first output filter data and the second output filter data.

A filtering method for a finite impulse response filter having a filter length L and comprising at least first and second ROM banks formed by a plurality of ROMs for storing filter state values in accordance with a predetermined number of taps, a first delay portion for delaying input data of a predetermined impulse form by L/2 delay steps according to a predetermined symbol rate, and a second delay portion for delaying the data finally delayed and output by said first delay portion by L/2 steps, said method comprising the steps of:

• generating first addresses by selectively performing a ones complement operation on data output by (L/2)-1 of said L/2 delay steps of said first delay portion or outputting said data output by said (L/2)-1 delay steps as is, in response to a value of data output by an initial delay step of said first delay portion;
• generating second addresses by selectively performing a ones complement operation on data output by (L/2)-1 of said L/2 delay steps of said second delay portion or outputting said data output by said (L/2)-1 delay steps of said second delay portion as is, in response to a value of data output by a final delay step of said second delay portion;
• outputting filter state values stored in said ROMs of said first ROM bank in response to said first addresses;
• outputting filter state values stored in said ROMs of said second ROM bank in response to said second addresses;
• multiplexing, for output, said filter state values output by said ROMS of said first ROM bank in response to a first clock having an oversampling rate/2 times as large as said symbol rate;
• multiplexing, for output, said filter state values output by said ROMS of said second ROM bank in response to second clock having a reverse sequence of said first clock;
• selectively performing a twos complement operation on said filter state values output by said ROMs of said first ROM bank or directly outputting said filter state values output from said ROMs of said first ROM bank, in response to said value of data output by said initial delay step of said first delay portion;
• selectively performing a twos complement operation on said filter state values output by said ROMs of said second ROM bank or directly outputting said filter state values output from said ROMs of said second ROM bank, in response to said value of said data output by said final delay step of said second delay portion;
• and
• outputting filter output data by summing the filter state values output during said step of selectively performing twos complement on said filter state values output by said ROMs of said first ROM bank or directly outputting said filter state values output from said ROMs of said first ROM bank and said step of selectively performing twos complement on said filter state values output by said ROMs of said second ROM bank or directly outputting said filter state values output from said ROMs of said second ROM bank.

A filtering method for a finite impulse response filter having a filter length L and comprising at least a lookup table for storing filter state values in accordance with a predetermined number of taps, a first delay means having L/2 delay devices and for delaying input data of a predetermined impulse form by L/2 steps according to a predetermined symbol rate, and a second delay means having L/2 delay devices symmetrically corresponding to the respective delay devices of said first delay means for delaying the data output by the final delay device of said first delay means by L/2 steps, said method comprising the steps of:

• applying, respectively, data output by each of said L/2 delay devices of said first delay means to a first input terminal of respective L/2 multiplexers;
• applying, respectively, data output by each of said L/2 delay devices of said second delay means to a second input terminal of said L/2 multiplexers;
• generating a control signal by multiplexing data output by an initial delay step of said first delay means and data output by a final delay step of said second delay means by a first one of said L/2 multiplexers in response to a first clock having a rate four times as large as said symbol rate;
• generating (L/2)-1 address bits by multiplexing, in response to said first clock signal, data output by the remaining (L/2)-1 delay steps of said L/2 delay steps of said first and second delay means, the final delay step of said first delay means and the initial delay step of said second delay means being multiplexed by one of the remaining (L/2)-1 multiplexers to produce a least significant bit of said (L/2)-1 address bits;
• generating a first output signal and a second output signal by counting a second clock having a rate two times as large as said symbol rate according to a predetermined oversampling rate in a first counting direction and in a second counting direction the reverse of said first counting direction, respectively;
• generating an address bit pair, said address bit pair being used in combination with said (L/2)-1 address bits as a most significant bit and next most significant bit of an address for addressing said lookup table, by applying said first and second output signals to an additional multiplexer in response to said first clock;
• applying said control signal to a first input terminal of (L/2)-1 exclusive-OR gates;
• applying said (L/2)-1 address bits to respective ones of second input terminals of said (L/2)-1 exclusive OR gates;
• outputting filter state values from said lookup table in response to said address bit pair and outputs of said (L/2)-1 exclusive OR gates;
• selectively performing a twos complement operation on said filter state values output by said lookup table or directly outputting said filter state values output from said lookup table, in response to a value of said control signal;
• temporarily storing the filter state values output from said step of performing a twos complement operation on said filter state values output by said lookup table or the filter state values output from said step of directly outputting said filter state values output from said lookup table;
• and
• generating filter output data by summing the temporarily stored filter state values and the filter state values output from said step of performing a twos complement operation on said filter state values output by said lookup table or the filter state values output from said step of directly outputting said filter state values output from said lookup table.

A filtering method for a finite impulse response filter having a filter length L and comprising at least a ROM bank made up with a plurality of ROMs and for storing filter state values in accordance with a predetermined number of taps, a first delay means having L/2 delay devices and for delaying input data of a predetermined impulse form by L/2 steps according to a predetermined symbol rate, and a second delay means having L/2 delay devices for delaying the data output by the final delay device of said first delay means by L/2 steps, said method comprising the steps of:

• counting a first clock having a rate two times as large as said symbol rate according to a predetermined oversampling rate, and outputting a first output signal indicative of a counting result obtained by counting in a first counting direction, and a second output signal indicative of reverse sequence of said counting result;
• multiplexing, for output, said first and second output signals in response to a second clock having a rate four times as large as said symbol rate;
• generating a control signal by multiplexing an output value of an initial delay step performed by said first delay means and an output value of a final delay step performed by said second delay means in response to said second clock;
• generating (L/2)-1 address bits by multiplexing output values, excluding the output value of said initial delay step of said first delay means, of said first delay means with output values, excluding the final delay step of said second delay means, of said second delay means, in response to said second clock;
• applying said control signal to a first input terminal of (L/2)-1 exclusive-OR gates;
• applying respective ones of said (L/2)-1 address bits to a second input terminal of respective ones of said (L/2)-1 exclusive-OR gates;
• addressing filter state values stored in said ROMs of said ROM bank in response to output values generated by said (L/2)-1 exclusive-OR gates;
• multiplexing the filter state values output from said ROMs of said ROM bank, in response to an output obtained by said step of multiplexing said first and second output signals;
• selectively performing a twos complement operation on said filter state values output by said step of multiplexing the filter state values output from said ROMs of said ROM bank or directly outputting said filter state values output by said step of multiplexing the filter state values output from said ROMs of said ROM bank, in response to a value of said control signal;
• temporarily storing the filter state values output from said step of performing a twos complement operation or the filter state values output from said step of directly outputting said filter state values;
• and
• generating filter output data by summing the temporarily stored filter state values and the filter state values output from said step of performing a twos complement operation or the filter state values output from said step of directly outputting said filter state values.