Optimized multi-pam finite impulse response (FIR) filter
A receiver circuit is disclosed. The receiver circuit includes a multi-PAM input circuit to receive a multi-PAM input symbol. The input symbol exhibits one of multiple threshold levels during a sampling period. The threshold levels correspond to a set of M-bit two's-complement values within a defined set of threshold values. An adaptive filtering circuit includes a first transcoder to transcode the set of M-bit two's-complement values to a set of N-bit values, where N<M. An adaptive filter operates to filter the set of N-bit values to generate a filtered set of data values. A second transcoder transforms the filtered set of data values to a second set of data values that corresponds to a set of filtered M-bit two's-complement values.
1. A receiver circuit, comprising:
a multi-PAM input circuit configured to receive a multi-PAM input symbol, the input symbol exhibiting a signal level that falls within one of multiple signal ranges during a sampling period, the signal ranges corresponding to a first set of M-bit two's-complement values, the multi-PAM input circuit configured to identify the input symbol signal level and corresponding M-bit two's-complement code corresponding to the identified signal level; and
an adaptive filtering circuit including
a first transcoder to transcode the identified M-bit two's-complement code to an N-bit code representing a value from a set of N-bit two's complement values, wherein N<M;
an adaptive filter to receive the N-bit code and to generate a filtered data value; and
a second transcoder to transform the filtered data value to a second data value that corresponds to a filtered M-bit two's-complement value.
2. The receiver circuit according to claim 1 , wherein:
the multi-PAM input circuit comprises a PAM4 input circuit to receive PAM4 input symbols.
3. The receiver circuit according to claim 2 , wherein the first set of M-bit two's complement values comprises:
a set of 3-bit two's-complement values corresponding to the set (−3, −1, +1, +3).
4. The receiver circuit according to claim 2 , wherein the second set of N-bit two's complement values comprises:
a set of 2-bit two's-complement values corresponding to the set (−2, −1, 0, +1).
5. The receiver circuit according to claim 2 , wherein:
the adaptive filter comprises a finite impulse response (FIR) filter.
6. The receiver circuit according to claim 5 , wherein:
the adaptive filter includes at least three taps.
7. The receiver circuit according to claim 6 , wherein:
each of the at least three taps generates a single partial product; and
the adaptive filter is configured to generate a sum of the single partial products from each of the at least three taps.
8. An adaptive filtering circuit including
a first transcoder to transcode a multi-PAM input symbol encoded in a first M-bit two's-complement value to an N-bit value, wherein N<M;
an adaptive filter to receive the N-bit value and generate a filtered data value; and
a second transcoder to transform the filtered data value to a second data value that corresponds to a filtered M-bit two's-complement value.
9. The adaptive filter circuit according to claim 8 , wherein the first M-bit two's complement values comprises:
a 3-bit two's-complement value corresponding to one from the set of values represented by (−3, −1, +1, +3).
10. The adaptive filter circuit according to claim 8 , wherein the N-bit value comprises:
a 2-bit value corresponding to one from the set of values represented by (−2, −1, 0, +1).
11. The adaptive filter circuit according to claim 8 , embodied as a finite impulse response (FIR) filter.
12. The adaptive filter circuit according to claim 11 , further comprising:
at least three taps.
13. The adaptive filter circuit according to claim 12 , wherein:
each of the at least three taps generates a single partial product; and
the adaptive filter is configured to generate a sum of the single partial products from each of the at least three taps.
14. A method of operation for a receiver circuit, the method comprising:
receiving a multi-PAM input symbol, the input symbol exhibiting a signal level that falls within one of multiple signal ranges during a sampling period, the signal ranges corresponding to a first set of M-bit two's-complement values;
identifying the input symbol signal level and corresponding M-bit two's-complement code corresponding to the identified signal level; and
adaptively filtering the multi-PAM input symbol, including
transcoding the identified M-bit two's-complement code, with a first transcoder, to an N-bit code representing a value from a set of N-bit two's complement values, wherein N<M;
adaptively filtering the N-bit code to generate a filtered data value; and
recoding the filtered data value to a second data value that corresponds to a filtered M-bit two's-complement value.
15. The method according to claim 14 , wherein:
the receiving of the multi-PAM input symbol comprises receiving a PAM4 input symbol.