IIR DFE updating gain and time constants using LMS equations
A method for adapting a mixed signal Infinite Impulse Response (IIR) Decision Feedback Equalizer (DFE) using pivot taps and monitor taps is disclosed. The method includes, for a given IIR path for a received signal, updating gain of the given IIR path using a respective pivot tap error-data correlation with a first Least Mean Square (LMS) update equation; and updating a time constant of the given IIR path using a respective monitor tap error-data correlation with a second LMS update equation.
1. A Decision Feedback Equalizer (DFE) comprising:
a set of data slicers connected to provide a signal to a data delay line having a plurality of digital delay blocks, the set of data slicers further connected to receive an input signal that has been provided through an adder; and
a first Infinite Impulse Response (IIR) tap for a first IIR path, the first IIR tap comprising a first digital-to-analog converter (DAC) and a first filter, the first IIR tap being connected to receive a signal output from a respective digital delay block that has been selected for a pivot tap for the first IIR path and further being connected to provide a correction signal to the adder;
in which coefficients for the first DAC are connected to be updated using a respective pivot tap error-data correlation with a first Least Mean Square (LMS) update equation and coefficients for the first filter are connected to be updated using a respective error-data correlation for a monitor tap for the first IIR path with a second LMS update equation; and
at least one additional IIR tap for a respective IIR path, each additional IIR tap including:
a respective DAC and a respective filter;
each additional IIR tap being connected to receive the signal from a respective digital delay block that has been selected for a pivot tap for the additional IIR path and to provide a respective correction signal to the adder;
in which coefficients for the respective DAC are connected to be updated using another respective pivot tap error-data correlation with the first Least Mean Square (LMS) update equation; and
coefficients for the respective filter are updated using another respective error-data correlation for a monitor tap for the additional IIR path with the second LMS update equation.
2. The DFE as recited in claim 1 in which adaptation of the first IIR path is performed alternately with adaptation of the at least one additional IIR path every adaptation period.
3. The DFE as recited in claim 2 wherein the adaptation period is increased in length once steady state operation is achieved.
4. The DFE as recited in claim 3 wherein the adaptation of the first IIR path and the at least one additional IIR paths starts with an IIR path having a longest time constant and successively adapts IIR paths having a next longest time constant.
5. The DFE as recited in claim 3 wherein the adaptation of the first IIR path and the at least one additional IIR paths starts with an IIR path having a shortest time constant and successively adapts IIR paths having a next shortest time constant.
6. The DFE as recited in claim 3 further comprising one or more Finite Impulse Response (FIR) taps each comprising a respective DAC and being connected to receive the signal from a respective digital delay block that has been selected for a FIR tap and further being connected to provide a correction signal to the adder.
7. A receiver for a high-speed signal, comprising:
a Continuous Time Linear Equalizer connected to receive the high-speed signal, to cancel Inter-Signal Interference (ISI) and provide a partially equalized signal; and
a Decision Feedback Equalizer (DFE) connected to receive the partially equalized signal and to provide an output signal containing recognized symbols, the DFE comprising
a set of data slicers connected to provide a signal to a data delay line having a plurality of digital delay blocks, the set of data slicers further connected to receive an input signal that has been provided through an adder; and
a first Infinite Impulse Response (IIR) tap for a first IIR path, the first IIR tap comprising a first digital-to-analog converter (DAC) and a first filter, the first IIR tap being connected to receive a signal from a respective digital delay block that has been selected for a pivot tap for the first IIR path and further being connected to provide a correction signal to the adder;
in which coefficients for the first DAC are connected to be updated using a respective pivot tap error-data correlation with a first Least Mean Square (LMS) update equation and coefficients for the first filter are connected to be updated using a respective error-data correlation for a monitor tap for the first IIR path with a second LMS update equation; and
at least one additional IIR tap for a respective IIR path, each additional IIR tap including a respective DAC and a respective filter;
each additional IIR tap being connected to receive the signal from a respective digital delay block that has been selected for a pivot tap for the respective IIR path and to provide a respective correction signal to the adder;
in which coefficients for the respective DAC are connected to be updated using another respective pivot tap error-data correlation with the first Least Mean Square (LMS) update equation; and
coefficients for the respective filter are updated using another respective error-data correlation for a monitor tap for the respective IIR path with the second LMS update equation.
8. The receiver for the high-speed signal as recited in claim 7 in which adaptation of the first IIR path is performed alternately with adaptation of the at least one additional IIR path every adaptation period.