Adaptive FIR filter and method
OwnerHiroshi Takatori, Chien-Hsin Leeinventors
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Abstract
Finite impulse response filters are commonly used in high speed data communications electronics for reducing error rates in multilevel symbol encoding schemes. Schemes such as pulse amplitude modulation and quadrature amplitude modulation may have higher error rates for symbols with low signal to noise ratios. By selectively updating the tap coefficients of the filter based on the symbols received, a more robust, accurate filter can be built.
Claims15
A finite impulse response filter comprising:
- a block configured to generate a coefficient adjustment signal based, at least in part, on a voltage level of a received symbol in a pulse amplitude-modulated signal;
- an integrator configured to generate an undated filter coefficient based, at least in part, on a tap coefficient associated with the finite impulse response filter and the coefficient adjustment signal;
- and
- a multiplier coupled to the integrator and configured to multiply the received symbol with the updated filter coefficient to generate a correction signal;
- wherein the block is further configured to generate the coefficient adjustment signal with a value such that the updated filter coefficient is equal to the tap coefficient in response to receipt of a symbol having a first specific voltage level and to generate the coefficient adjustment signal with a value such that the updated filter coefficient is different from the tap coefficient in response to receipt of a symbol having a second specific voltage level.
A method of adjusting a tap coefficient for a finite impulse response filter, the method comprising:
- in response to receipt of a pulse amplitude-modulated signal including a first data symbol having a first specific voltage level, adjusting the filter coefficient based on a sign of the received first data symbol and a sign of an error signal corresponding to a difference between the received first data symbol and a decoded data signal;
- and
- maintaining a constant tap coefficient in response to receipt of a second data symbol having a second specific voltage level.
A decision feedback equalizer comprising:
- a decision circuit configured to receive a data signal and output decoded data;
- an error calculator configured to generate an error signal corresponding to a difference between the data signal and the decoded data;
- a plurality of taps coupled in series, wherein the plurality of taps are configured to receive a data signal, delay the data signal, and couple the delayed data signal to a next tap, each tap comprising a finite impulse response filter having a corresponding filter coefficient, wherein each finite impulse response filter is configured to generate a correction signal based on the data signal and the filter coefficient, and wherein each finite impulse response filter includes a filter coefficient updater configured to update the filter coefficient based, at least in part, on a specific voltage level of a received symbol;
- and
- a summer configured to receive the respective correction signals from the plurality of taps, wherein the summer is coupled to the decision circuit and configured to receive an input signal and to generate the data signal based, at least in part, on the correction signals.
A finite impulse response filter having an associated filter coefficient, the finite impulse response filter comprising:
- means for delaying an input signal;
- means for updating the filter coefficient based on the filter coefficient and a symbol of the delayed input signal, wherein the filter coefficient is updated to a different filter coefficient in response to receipt of a first symbol having a first specific voltage level, and wherein the filter coefficient is maintained constant in response to receipt of a second symbol having a second specific voltage level;
- and
- means for generating a correction signal based on the delayed input signal and the updated filter coefficient.
Dependencies are inferred from the claim text.