High-speed receiver architecture
View Patent ↗A receiver (e.g., for a 10G fiber communications link) includes an interleaved ADC coupled to a multi-channel equalizer that can provide different equalization for different ADC channels within the interleaved ADC. That is, the multi-channel equalizer can compensate for channel-dependent impairments. In one approach, the multi-channel equalizer is a feedforward equalizer (FFE) coupled to a Viterbi decoder, for example a sliding block Viterbi decoder (SBVD); and the FFE and/or the channel estimator for the Viterbi decoder are adapted using the LMS algorithm.
1. A transceiver chip for communication over a fiber optic, the transceiver chip comprising:
a host interface for receiving digital data in electrical form, the received digital data in a host format;
a laser driver port for generating an electrical signal modulated by the received digital data in electrical form, the electrical signal suitable for driving a laser driver;
transmit path circuitry coupled between the host interface and the laser driver port;
an input port for receiving an electrical signal from a transimpedance amplifier, the received electrical signal modulated by data; and
receive path circuitry coupled between the input port and the host interface, the host interface further for transmitting digital data in electrical form, the transmitted digital data also in the host format, the receive path circuitry comprising:
an analog-to-digital converter to receive the electrical signal from the transimpedance amplifier via the input port, and to generate signal samples from the received electrical signal, the received electrical signal having combined non-Gaussian noise and Gaussian noise;
a feedforward equalizer coupled to receive the signal samples from the analog-to-digital converter, and to apply equalization based on a cumulative metric function to generate equalized samples, the cumulative metric function to compensate for the combined non-Gaussian noise and Gaussian noise in the received signal samples, wherein the cumulative metric function is approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric function, ŷ n represents a symbol at an output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1;
a decoder coupled to the output of the feedforward equalizer, the decoder determining detected symbols based on the equalized samples and a channel model; and
a channel estimator coupled to receive the output of the feedforward equalizer and an output of the decoder and generate the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal.
2. The transceiver chip of claim 1 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order noise parameters and where S 0 =f(0,0, . . . , 0), S 1 =f(1,1, . . . , 1).
3. The transceiver chip of claim 1 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function LUT(ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .
4. A receiver comprising:
an analog-to-digital converter that generates signal samples from a received signal having combined non-Gaussian noise and Gaussian noise;
a feedforward equalizer coupled to receive the signal samples from the analog-to-digital converter, and to apply equalization based on a cumulative metric function to generate equalized samples, the cumulative metric function to compensate for the combined non-Gaussian noise and Gaussian noise in the received signal samples, wherein the cumulative metric function is approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric function, ŷ n represents a symbol at an output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1;
a decoder coupled to the output of the feedforward equalizer, the decoder determining detected symbols based on the equalized samples and a channel model; and
a channel estimator coupled to receive the output of the feedforward equalizer and an output of the decoder and generate the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal.
5. The receiver of claim 4 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order noise parameters and where S 0 =f(0,0, . . . , 0), S 1 =f(1,1, . . . , 1).
6. The receiver of claim 4 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function LUT(ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .
7. The receiver of claim 4 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function y v ≈y v ref └1+(v−v ref )log(y)+0.5(v−v ref ) 2 (log(y)) 2 ┘ where V ref is a tabulated reference.
8. The receiver of claim 4 , further comprising:
a transformation block to provide an approximate solution to (ŷ n ) v , wherein the transformation block implements a function K −1 ŷ 0.5 +(v−0.5)ŷ where K is a constant.
9. The receiver of claim 4 , where v is given by v=0.5 if M 2,1 /M 2,0 >K 0.5 and by v=1, where K 0.5 is a programmable threshold level.
10. The receiver of claim 4 , wherein the non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.
11. A method for equalizing a received signal, the method comprising:
generating, by an analog-to-digital converter, signal samples from the received signal having combined non-Gaussian noise and Gaussian noise;
applying, by a feedforward equalizer, an equalization to the signal samples from the analog-to-digital converter based on a cumulative metric function to generate equalized samples, the cumulative metric function to compensate for the combined non-Gaussian noise and Gaussian noise in the received signal samples, wherein the cumulative metric function is approximated by M≈Σ n [(ŷ n ) v −(ŝ n ) v ] 2 where M is the cumulative metric function, ŷ n represents a symbol at an output of the feedforward equalizer, ŝ n is a noise-free signal component of ŷ n , where 0<v≦1;
determining, by a decoder coupled to the output of the feedforward equalizer, detected symbols based on the equalized samples and a channel model; and
generating, by a channel estimator the channel model and an error feedback signal to adaptively update coefficients of the feedforward equalizer based on the error feedback signal.
12. The method of claim 11 , where v is given by
v
≈
1
+
0.5
log
(
M
2
,
1
/
M
2
,
0
)
log
(
S
0
/
S
1
)
,
where M 2,0 and M 2,1 are conditional second-order noise parameters and where S 0 =f(0,0, . . . , 0), S 1 =f(1,1, . . . , 1).
13. The method of claim 11 , further comprising:
providing an approximate solution to (ŷ n ) v , by implementing a function LUT(ŷ n )=(ŷ n +y min ) v when the sample ŷ n is in an interval between −y min and +y min .
14. The method of claim 11 , further comprising:
providing an approximate solution to (ŷ n ) v , by implementing a function y v ≈y v ref └1+(v−v ref )log(y)+0.5(v−v ref ) 2 (log(y)) 2 ┘ where v ref is a tabulated reference.
15. The method of claim 11 , further comprising:
providing an approximate solution to (ŷ n ) v , by implementing a function K −1 ŷ 0.5 +(v−0.5)ŷ where K is a constant.
16. The method of claim 11 , where v is given by v=0.5 if M 2,1 /M 2,0 >K 0.5 and by v=1, where K 0.5 is a programmable threshold level.
17. The method of claim 11 , wherein the non-Gaussian noise comprises amplified spontaneous emission (ASE) noise.