Multi-channel equalization to compensate for impairments introduced by interleaved devices
View Patent ↗A system includes a time-interleaved device. An equalizer effectively can apply different equalization to different interleaved channels. For convenience, these equalizers will be referred to as multi-channel equalizers. In one aspect, an apparatus includes an interleaved device having M interleaved channels, and a multi-channel equalizer coupled to the interleaved device. The multi-channel equalizer is capable of applying a different equalization to different interleaved channels, thus compensating for channel-dependent impairments.
1. An apparatus comprising:
an interleaved analog to digital converter (ADC) having M interleaved ADC channels,
the interleaved ADC comprising:
an input port for receiving an analog input signal;
a programmable gain amplifier coupled to the input port;
M ADC channels, each coupled to an output of the programmable gain amplifier, each ADC channel including a track-and-hold unit coupled to ADC conversion circuitry;
retimer circuitry coupled to the ADC channels to combine digital output signals from the ADC channels into a digital output signal for the interleaved ADC;
an output port coupled to the retimer circuitry;
automatic gain control coupled between the retimer circuitry and the programmable gain amplifier, for adjusting a gain of the programmable gain amplifier; and
a timing recovery circuit and analog phase interpolator, coupled to an output of the retimer circuitry for adjusting a phase of a clock input to the track-and-hold units; and
a multi-channel equalizer coupled to an output of the interleaved ADC, the multi-channel equalizer capable of applying a different equalization to different interleaved ADC channels.
2. The apparatus of claim 1 wherein the multi-channel equalizer comprises a feedforward equalizer.
3. The apparatus of claim 1 wherein:
the multi-channel equalizer comprises:
a Viterbi decoder coupled to an output of the feedforward equalizer, the decoder producing an output of the multi-channel equalizer; and
a channel estimator coupled to outputs of the feedforward equalizer and the Viterbi decoder, and coupled to an input of the Viterbi decoder.
4. The apparatus of claim 1 wherein the multi-channel equalizer comprises a maximum likelihood sequence estimators (MLSE) equalizer.
5. The apparatus of claim 1 wherein the multi-channel equalizer comprises a decision feedback equalizers (DFE) equalizer.
6. The apparatus of claim 5 wherein:
the multi-channel equalizer comprises:
a feedforward equalizer coupled to the output port of the interleaved ADC;
a feedback equalizer;
a summer coupled between to receive outputs from the feedforward equalizer and the feedback equalizer; and
a slicer coupled to receive an output of the summer, an output of the slicer producing an output for the multi-channel equalizer, wherein said output is coupled to an input of the feedback equalizer.
7. The apparatus of claim 1 wherein the multi-channel equalizer comprises:
an N-tap, M-parallel impulse response (FIR).
8. The apparatus of claim 7 wherein the N-tap, M-parallel FIR comprises M processing elements, each processing element including N multipliers to multiply input signals by tap weights to produce intermediate products, and a plurality of adders to sum the intermediate products.
9. The apparatus of claim 7 wherein the N-tap, M-parallel FIR comprises M processing elements, each processing element including N lookup tables to generate intermediate products based on input signals, and a plurality of adders to sum the intermediate products.
10. The apparatus of claim 1 further comprising:
a photodetector for receiving an optical waveform transported across an optical fiber, the optical waveform carrying data.
11. The apparatus of claim 10 wherein the multi-channel equalizer comprises a maximum likelihood sequence estimators (MLSE) equalizer.
12. The apparatus of claim 10 wherein the multi-channel equalizer comprises a decision feedback equalizers (DFE) equalizer.
13. The apparatus of claim 10 wherein M=8.
14. The apparatus of claim 1 wherein the multi-channel equalizer has equalizer coefficients, each of which is dedicated exclusively to one of the M interleaved ADC channels.
15. The apparatus of claim 1 wherein the multi-channel equalizer has at least one equalizer coefficient that is shared by all M interleaved ADC channels.
16. The apparatus of claim 1 wherein the multi-channel equalizer has at least one equalizer coefficient that is shared by more than one but less than M interleaved ADC channels.
17. An apparatus comprising:
an interleaved device having M interleaved channels; and
a multi-channel equalizer coupled to the interleaved device, the multi-channel equalizer capable of applying a different equalization to different interleaved channels, the multi-channel equalizer comprising:
a feedforward equalizer coupled to an output of the interleaved device;
a decoder coupled to an output of the feedforward equalizer, the decoder producing an output of the multi-channel equalizer; and
a channel estimator coupled to outputs of the feedforward equalizer and the decoder, and coupled to an input of the decoder.
18. The apparatus of claim 17 where the interleaved device is an interleaved analog to digital converter (ADC) having M interleaved ADC channels.
19. The apparatus of claim 18 further comprising:
a photodetector for receiving an optical waveform transported across an optical fiber, the optical waveform carrying data.
20. The apparatus of claim 18 wherein M=8.
21. The apparatus of claim 18 wherein the multi-channel equalizer has equalizer coefficients, each of which is dedicated exclusively to one of the M interleaved ADC channels.
22. The apparatus of claim 18 wherein the multi-channel equalizer has at least one equalizer coefficient that is shared by all M interleaved ADC channels.
23. The apparatus of claim 18 wherein the multi-channel equalizer has at least one equalizer coefficient that is shared by more than one but less than M interleaved ADC channels.