Digital serializer/deserializer circuit and data eye monitoring method thereof
The application disclose a digital serializer/deserializer circuit and a data eye monitoring method thereof. A received analog signal is converted to first digital samples at a first sample rate. The first digital samples are equalized to generate a first equalized signal. A symbol decision signal is generated from the first equalized signal. The received analog signal is converted to second digital samples at a second sample rate. Difference between the first digital samples and the second digital samples is determined, and the first equalized signal and the determined difference are combined to generate a signal processing output. A data eye error rate is determined according to the symbol decision signal and the signal processing output.
1 . A digital serializer/deserializer circuit for a receiver, the digital serializer/deserializer circuit comprising a data path and a data eye monitoring path, wherein:
the data path comprises:
a first analog-to-digital converter (ADC), configured to convert a received analog signal to first digital samples at a first sample rate;
a first signal processing stage coupled to the first ADC, the first signal processing stage comprising an equalizer coupled to the first ADC for equalizing the first digital samples to generate a first equalized signal; and
a decision circuit coupled to the first signal processing stage for generating a symbol decision signal from the first equalized signal; and
the data eye monitoring path comprises:
a second ADC configured to convert the received analog signal to second digital samples at a second sample rate, and further configured to take samples at second sampling points different from the first sampling points at which the first ADC takes samples;
a second signal processing stage coupled to the second ADC, and configured to receive the first digital samples from an output of the first ADC prior to said first signal processing stage, determine a difference signal between the first digital samples and the second digital samples, and combine the first equalized signal and the difference signal to generate an output of the second signal processing stage; and
a data eye monitoring circuit coupled to the first signal processing stage and the second signal processing stage, and configured to determine a data eye error rate according to the symbol decision signal and the output of the second signal processing stage.
2 . The digital serializer/deserializer circuit according to claim 1 , wherein the second sample rate is equal to or lower than the first sample rate.
3 . The digital serializer/deserializer circuit according to claim 1 , wherein the equalizer comprises:
a feed-forward equalizer (FFE) coupled to the first ADC for filtering the first digital samples to generate a feed forward equalized signal;
a decision feedback equalizer (DFE) coupled to the decision circuit for processing the symbol decision signal to generate a decision feedback equalized signal; and
a combining circuit coupled to the FFE and the DFE for combining the feed forward equalized signal and the decision feedback equalized signal to generate the first equalized signal.
4 . The digital serializer/deserializer circuit according to claim 1 , wherein the output of the second signal processing stage is represented by a formula: s[n]+w 0 (y(nT+τ)−y(nT)), wherein: s[n] represents the first equalized signal, w 0 is a weighting coefficient, y(nT) represents the first digital samples which are samples of the received analog signal at times nT, y(nT+τ) represents the second digital samples which are samples of the received analog signal at times nT+τ, T is the sampling period, and τ is a time offset.
5 . The digital serializer/deserializer circuit according to claim 4 , wherein the weighting coefficient is corresponding to a main tap coefficient of an FFE within the equalizer.
6 . The digital serializer/deserializer circuit according to claim 5 , wherein the main tap coefficient of the FFE is set as 1.
7 . The digital serializer/deserializer circuit according to claim 1 , wherein the second signal processing stage comprises two adders and one multiplier, wherein the multiplier is configured to multiply the difference signal by a weighting coefficient which is corresponding to a main tap coefficient of an FFE within the equalizer.
8 . The digital serializer/deserializer circuit according to claim 1 , wherein the data eye monitoring circuit comprises:
a slicing circuit coupled to the second signal processing stage, and configured to output slicing samples above a plurality of adjustable data eye thresholds; and
an error rate circuit coupled to the slicing circuit, and configured to determine the data eye error rate according to the symbol decision signal and the slicing samples.
9 . The digital serializer/deserializer circuit according to claim 1 , wherein the received analog signal is of PAM-N signaling and the data eye monitoring circuit comprises:
a histogram circuit coupled to the second signal processing stage, the histogram circuit having a plurality of different histograms for the PAM-N signaling, wherein the histogram circuit is configured to determine which histogram for the output of the second signal processing stage based on the symbol decision signal and the output of the second signal processing stage, and generate a histogram for the output of the second signal processing stage, and
a computation circuit coupled to the histogram circuit, and configured to determine a data eye height and a data eye width based on the histogram from the histogram circuit to determine the data eye error rate.
10 . A digital serializer/deserializer circuit for a receiver, the digital serializer/deserializer circuit comprising a data path and a data eye monitoring path, wherein:
the data path comprises:
a first analog-to-digital converter (ADC) configured to convert a received analog signal to first digital samples at a first sample rate;
a first signal processing stage coupled to the first ADC, the first signal processing stage comprising an equalizer coupled to the ADC for equalizing the first digital samples to generate a first equalized signal; and
a decision circuit coupled to the first signal processing stage for generating a symbol decision signal from the first equalized signal; and
the data eye monitoring path comprises:
a slicing circuit coupled to the first ADC and the first signal processing stage, and further configured to slice the received analog signal according to a slicer level to generate second digital samples at a second sample rate, wherein the slicer level is determined according to the first equalized signal and the first digital samples; and
a data eye monitoring circuit coupled to the slicing circuit, and configured to determine a data eye error rate according to the symbol decision signal and the second digital samples,
wherein the digital serializer/deserializer circuit further comprises:
a first digital-analog converter (DAC) coupled to the first ADC and the slicing circuit, and configured to convert the first digital samples into a first analog signal which is used to determine the slicer level;
a multiplier coupled to the first signal processing stage, for multiplying a reciprocal of a main tap coefficient of an FFE of the first signal processing stage with the first equalized signal to generate a multiplication result; and
a second DAC coupled to the multiplier, for converting the multiplication result into a second analog signal which is used to determine the slicer level.
11 . The digital serializer/deserializer circuit according to claim 10 , wherein the equalizer comprises:
a feed-forward equalizer (FFE) coupled to the first ADC for filtering the first digital samples to generate a feed forward equalized signal;
a decision feedback equalizer (DFE) coupled to the decision circuit for processing the symbol decision signal to generate a decision feedback equalized signal; and
a combining circuit coupled to the FFE and the DFE for combining the feed forward equalized signal and the decision feedback equalized signal to generate the first equalized signal.
12 . The digital serializer/deserializer circuit according to claim 10 , wherein the second digital samples are derived by the slicing circuit at second sampling points different from the first sampling points at which the first digital samples are derived, and the second sample rate is lower than the first sample rate.
13 . A data eye monitoring method of a digital serializer/deserializer circuit for a receiver, the data eye monitoring method including:
converting a received analog signal to first digital samples at a first sample rate;
equalizing the first digital samples to generate a first equalized signal;
generating a symbol decision signal from the first equalized signal;
converting the received analog signal to second digital samples at a second sample rate, the second digital samples being sampled at second sampling points different from the first sampling points at which the first digital samples are sampled;
receiving the first digital samples prior to equalization of the first digital samples, determining a difference signal between the first digital samples and the second digital samples, and combining the first equalized signal and the difference signal to generate a signal processing output; and
determining a data eye error rate according to the symbol decision signal and the signal processing output.
14 . The data eye monitoring method according to claim 13 , wherein
the second sample rate is equal to or lower than the first sample rate;
equalizing the first digital samples to generate the first equalized signal includes:
filtering the first digital samples to generate a feed forward equalized signal;
processing the symbol decision signal to generate a decision feedback equalized signal; and
combining the feed forward equalized signal and the decision feedback equalized signal to generate the first equalized signal.
15 . The data eye monitoring method according to claim 13 , wherein the signal processing output is represented by a formula s[n]+w 0 (y(nT+τ)−y(nT)), wherein: s[n] represents the first equalized signal, w 0 is a weighting coefficient, y(nT) represents the first digital samples which are samples of the received analog signal at times nT, y(nT+τ) represents the second digital samples which are samples of the received analog signal at times nT+τ, T is the sampling period, and τ is a time offset.
16 . The data eye monitoring method according to claim 15 , wherein
the weighting coefficient is corresponding to a main tap coefficient of an FFE; or
the main tap coefficient of the FFE is set as 1.
17 . The data eye monitoring method according to claim 13 , wherein the signal processing stage comprises two adders and one multiplier, wherein the multiplier is configured to multiply the difference signal by a weighting coefficient which is corresponding to a main tap coefficient of an FFE.
18 . The data eye monitoring method according to claim 13 , further comprising:
outputting slicing samples above a plurality of adjustable data eye thresholds; and
determining the data eye error rate according to the symbol decision signal and the slicing samples.
19 . The data eye monitoring method according to claim 13 , wherein
the received analog signal is of PAM-N signaling; and
the data eye monitoring method further comprises:
determining which histogram for the signal processing output based on the symbol decision signal and the signal processing output, and generating a histogram for the signal processing output, and
determining a data eye height and a data eye width based on the histogram to determine the data eye error rate.