Adaptive equalizer and designing method thereof
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorsShuji Murakami, Hirohisa Machida, Hiroyuki Mizutani, Hiroshi Ochi
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Abstract
Following arrangement of an adaptive equalizer with a direct filter structure according to the least mean square error architecture, look ahead conversion of modifying a tap coefficient of the next cycle utilizing the tap coefficient of a predetermined preceding cycle is carried out and then a retiming process of adjusting the timing of tap coefficients and signals is carried out to arrange delay elements, whereby a transposition filter is realized. A high-speed adaptive equalizer is provided that can have the critical path reduced without increasing the hardware amount and that is superior in expansionability.
Claims16
An adaptive equalizer comprising:
- a filter processing unit including a plurality of cascaded processing stages provided corresponding to taps, each of said processing stages including (i) a first multiplier for multiplying an input signal by a corresponding tap coefficient, (ii) a delay stage for delaying an output signal of a preceding processing stage, and (iii) an adder for adding an output signal of said delay stage with an output signal of said first multiplier to provide an addition result to a next stage, the processing stage at a first stage including a multiplier for multiplying said input signal by a corresponding tap coefficient to provide a resultant signal to a subsequent processing stage at a next stage;
- and
- a tap coefficient set circuit for setting the tap coefficients according to an error between an output signal of said filter processing unit and a reference signal, said tap coefficient set circuit including a coefficient correction stage of a same structure provided corresponding to each tap coefficient and having a transfer function given by a product of the transfer function of an all pole filter and a transfer function of an all zero filter.
An adaptive equalizer comprising:
- a filter processing unit including a plurality of processing stages corresponding to taps and connected in series with each other, and having a forward path and a backward path, each of said plurality of processing stages including (i) a multiplier for multiplying an input signal applied on the forward path by a corresponding tap coefficient, (ii) an adder arranged on the backward path, for adding a signal on the backward path transmitted from a subsequent processing stage with an output signal of said multiplier for transmission onto the backward path,
- a delay stage providing a delay of 1 cycle interposed alternately at the processing stages in said forward path and said backward path;
- and
- a tap coefficient set circuit for setting said tap coefficients according to an error between an output signal of said filter processing unit and a reference signal, said tap coefficient set circuit including a coefficient correction stage of a same structure provided corresponding to each tap coefficient and having a transfer function given by a product of a transfer function of an all zero filter and a transfer function of an all pole filter.
A method of designing an adaptive equalizer correcting a tap coefficient so as to minimize an error between a reference signal and an output signal thereof, filtering an input signal according to the corrected tap coefficients and generating said output signal, said method comprising the steps of:
- arranging a filter processing stage and a tap coefficient set stage using a direct filter structure,
- carrying out look ahead conversion of relating a tap coefficient of a preceding-by-L cycle with the tap coefficient of a next cycle to rearrange said filter processing stage and said tap coefficient set stage,
- carrying out a retiming process for timing reorganization while maintaining time relationship of signals to reorganize an arrangement of delay elements for conversion into a transposition filter, and
- converting said tap coefficient set stage into a filter stage having a transfer function of (1−Z−L−1)/(1−Z−1) by equivalent conversion of a transfer function of the transposition filter.
Dependencies are inferred from the claim text.