Multi-tap decision feed-forward equalizer with precursor and postcursor taps
A multi-tap Differential Feedforward Equalizer (DFFE) configuration with both precursor and postcursor taps is provided. The DFFE has reduced noise and/or crosstalk characteristics when compared to a Feedforward Equalizer (FFE) since DFFE uses decision outputs of slicers as inputs to a finite impulse response (FIR) unlike FFE which uses actual analog signal inputs. The digital outputs of the tentative decision slicers are multiplied with tap coefficients to reduce noise. Further, since digital outputs are used as the multiplier inputs, the multipliers effectively work as adders which are less complex to implement. The decisions at the outputs of the tentative decision slicers are tentative and are used in a FIR filter to equalize the signal; the equalized signal may be provided as input to the next stage slicers. The bit-error-rate (BER) of the final stage decisions are lower or better than the BER of the previous stage tentative decisions.
1. A decision feedforward equalizer (DFFE), comprising:
a plurality of precursor taps configured to sample an input signal by different time delay amounts;
a plurality of postcursor taps configured to sample the input signal by the different time delay amounts;
a plurality of tentative decision slicers configured to receive the delayed signals from the plurality of precursor taps and the plurality of postcursor taps, and to quantize the delayed signals to generate quantized sampled signals;
a plurality of multipliers configured to receive the quantized sampled signals as outputs of the plurality of tentative decision slicers; and
an adder configured to receive outputs of the plurality of multipliers.
2. The DFFE of claim 1 , wherein the input signal is a non-equalized signal.
3. The DFFE of claim 1 , wherein the plurality of multipliers scales the quantized sampled signals by a filter tap coefficient to generate the outputs of the plurality of multipliers.
4. The DFFE of claim 3 , wherein the adder subtracts the outputs of the plurality of multipliers from the input signal.
5. The DFFE of claim 4 , wherein the adder provides an output that is precursor and postcursor inter-symbol interference compensated.
6. The DFFE of claim 1 , wherein the adder provides an output to a second DFFE.
7. The DFFE of claim 1 , wherein the input signal is received from a feedforward equalizer.
8. A decision feedforward equalizer (DFFE), comprising:
a first tentative decision slicer configured to receive a first delayed signal from a first precursor tap and quantize the first delayed signal to generate a first quantized sampled signal;
a second tentative decision slicer configured to receive a second delayed signal from a first postcursor tap and quantize the second delayed signal to generate a second quantized sampled signal;
a first multiplier configured to receive the first quantized sampled signal and scale the first quantized sampled signal by a first tap coefficient;
a second multiplier configured to receive the second quantized sampled signal and scale the second quantized sampled signal by a second tap coefficient;
an adder configured to receive outputs of the first multiplier, the second multiplier, and a cursor tap.
9. The DFFE of claim 8 , further comprising a plurality of precursor taps configured to sample an input signal by different time delay amounts, the plurality of precursor taps including the first precursor tap.
10. The DFFE of claim 8 , further comprising a plurality of postcursor taps configured to sample an input signal by different time delay amounts, the plurality of postcursor taps including the first postcursor tap.
11. The DFFE of claim 8 , wherein the first tap coefficient and the second tap coefficient are least mean square (LMS) coefficients.
12. The DFFE of claim 11 , wherein the adder subtracts the outputs of the first multiplier and the second multiplier from an input signal.
13. The DFFE of claim 12 , wherein the adder provides an output that is precursor and postcursor inter-symbol interference compensated.
14. The DFFE of claim 8 , wherein the adder provides an output to a second DFFE.
15. A method, comprising:
providing, from an output of a precursor tap, a first delayed signal to a first tentative decision slicer;
quantizing, by the first tentative decision slicer, the first delayed signal to generate a first quantized sampled signal;
providing, from an output of a postcursor tap, a second delayed signal to a second tentative decision slicer;
quantizing, by the second tentative decision slicer, the second delayed signal to generate a second quantized sampled signal;
providing the first quantized sampled signal and the second quantized sampled signal to a first multiplier and a second multiplier;
scaling, by the first multiplier and the second multiplier, the first quantized sampled signal and the second quantized sampled signal by a filter tap coefficient; and
providing a first scaled sampled signal and a second scaled sampled signal from the first multiplier and the second multiplier to a summation element for combining with other scaled sample signals.
16. The method of claim 15 , further comprising subtracting, by the summation element, the first scaled sampled signal, the second scaled sampled signal, and the other scaled sample signals from an input to the precursor tap and the postcursor tap.
17. The method of claim 16 , further comprising providing an output that is precursor and postcursor inter-symbol interference compensated.
18. The method of claim 15 , further comprising receiving, by the precursor tap and the postcursor tap, an input signal from a feedforward equalizer.
19. The method of claim 18 , wherein the precursor tap and the postcursor tap samples the input signal by a time amount.
20. The method of claim 18 , wherein the input signal includes amplified crosstalk and noise from the feedforward equalizer.