Systems and methods for interference cancellation
An apparatus for canceling clock-to-signal interference in a multi-lane SerDes comprising an analog front-end circuit receiving an input signal from a signal path mixed with interference from a clock path. The apparatus includes a phase interpolator circuit implemented in the clock path to generate multiple phases of a clock signal and to provide a timing rotated by the phases for a track-and-hold circuit to sample the input signal and the interference in every cycle. The apparatus also includes an analog-to-digital converter configured to digitize the input signal and the interference to provide an ADC output and a digital-interference-cancellation circuit configured to demultiplex the ADC output and detect a baseline offset associated with the interference sampled at one of the phases in each demultiplexed path using a digital loop to calibrate the baseline offset.
1 . An apparatus comprising:
an analog front-end (AFE) module receiving an input signal from a signal path mixed with an interference signal from a clock path;
a track-and-hold (T/H) circuit configured to sample the input signal;
a phase interpolator implemented in the clock path and configured to generate multiple phases of a clock signal and to provide a timing rotated by the phases for the T/H circuit to sample the input signal and the interference signal in every cycle;
an analog-to-digital converter (ADC) configured to digitize the input signal and the interference signal to provide an ADC output; and
a digital-interference-cancellation (DIC) circuit configured to demultiplex the ADC output and detect a baseline offset associated with the interference signal sampled at one of the phases in each demultiplexed path using a digital loop to calibrate the baseline offset.
2 . The apparatus of claim 1 , wherein the phase interpolator is configured to apply phase shifts of 2πn/N to generate the multiple phases, wherein n is an integer control code variable from 0 to N-1, to allow the T/H circuit to provide one sampled interference at corresponding one of the phases for a given n, wherein N is demultiplexing paths and an integer greater than one.
3 . The apparatus of claim 2 , wherein the DIC circuit is configured to detect the baseline offset resulting from the sampled interference at the same phase in every cycle for the control code n being at a fixed value.
4 . The apparatus of claim 2 , wherein the DIC circuit is configured to detect an additive periodic offset resulting from the sampled interference appeared at a rotating frequency given by 2πn/N for the control code n increasing linearly to track transmitting-receiving frequency offset.
5 . The apparatus of claim 2 , wherein the DIC circuit is configured to detect a random offset resulting from the sampled interference for the control code n changing randomly due to random jitter.
6 . The apparatus of claim 2 , wherein the T/H circuit is configured to sample the input signal as well as the interference signal with an optimized timing by detecting zero-crossings of the clock signal shifted by the multiple phases of 2πn/N.
7 . The apparatus of claim 3 , wherein the DIC circuit comprises a 1-to-N demultiplexer configured to demultiplex the ADC output to N paths, each path corresponding to the control code n comprising a digital accumulation filter to at least cancel a component of the baseline offset associated with the phase of 2πn/N.
8 . The apparatus of claim 7 , wherein the digital accumulation filter comprises an adaptive feedback loop using a factor of μ/(1−Z −1 ) to obtain an accumulated value in each demultiplexed path, where u is an adaptive rate and Z −1 represents a unit delay in the digital filter domain.
9 . The apparatus of claim 8 , wherein the DIC circuit further comprises an N-to-1 multiplexer to recombine the N paths to produce a single output with the accumulated value for each path being collectively recombined for canceling the baseline offset resulting from the sampled interference.
10 . The apparatus of claim 8 , wherein the DIC circuit is configured to be implemented in a background operation with the adaptive feedback loops concurrently with ongoing signal transmission with variations of process, voltage, and temperature.
11 . The apparatus of claim 3 , further comprises an analog-interference-cancellation (AIC) circuit configured with in-phase-quadrature (IQ) clock buffers in the clock path, the AIC circuit comprising a noise cancellation circuit configured to receive control parameters based on the baseline offset detected by the DIC circuit to generate an analog cancellation signal in a calibration loop.
12 . The apparatus of claim 11 , wherein the calibration loop is configured to use the control parameters in the IQ clock buffers to conduct iterative coarse/fine scans on finding real and imaginary components of the analog cancellation signal.
13 . The apparatus of claim 11 , wherein the AIC circuit is configured to operate in the foreground at system start-up time to inject the analog cancellation signal to the signal path to minimize a residue coupled clock noise entering the ADC circuit.
14 . An apparatus comprising:
an analog front-end (AFE) module configured to receive an input signal from a signal path mixed with an interference signal from a clock path;
a phase interpolator (PI) circuit implemented in the clock path and configured to generate multiple phases of a clock signal;
a track-and-hold (T/H) circuit configured to sample the input signal and the interference signal based on a timing rotated in the phases generated by the PI circuit in every cycle;
an analog-to-digital converter (ADC) configured to provide an ADC digital output based on a sampled input signal and a sampled interference at each of the multiple phases;
a digital-interference-cancellation (DIC) circuit configured to detect the sampled interference by demultiplexing the ADC digital output into multiple paths each comprising a digital adaptive loop; and
an analog-interference-cancellation (AIC) circuit implemented in the clock path to generate a cancellation signal based on a calibration loop using control parameters from the DIC circuit and to inject the cancellation signal to the signal path for canceling at least a part of the interference signal.
15 . The apparatus of claim 14 , wherein the PI circuit is configured to apply phase shifts of 2πn/N to generate the multiple phases, wherein n is an integer control code variable from 0 to N-1, to allow the T/H circuit to provide one sampled interference at corresponding one of the phases for a given n for the ADC circuit, wherein N is demultiplexing paths and an integer greater than one.
16 . The apparatus of claim 15 , wherein the DIC circuit is configured to detect a baseline offset in each digital adaptive loop at the phase of 2πn/N in every cycle per each n of the N demultiplexing paths, wherein accumulation of all baseline offsets in the N demultiplexing paths leads to determination of the control parameters for minimizing the amplitude of the sampled interference.
17 . The apparatus of claim 16 , wherein the AIC circuit is configured to determine a real-part component and an imaginary-part component in a calibration loop to generate the cancellation signal with a minimized residue difference in amplitude but with 180 degrees of phase difference relative to the interference signal.
18 . The apparatus of claim 17 , wherein the calibration loop is configured to independently determine the real-part component and the imaginary-part component using the control parameters in iterative coarse-control scans and fine-control scans.
19 . The apparatus of claim 18 , wherein the AIC circuit comprises a coupling cancellation circuit comprising four unit buffers for respectively tuning original and inverted in-phase and quadrature-phase components (I, Q, IB, QB) to perform the coarse-control scans, each unit buffer further comprising multiple sub-unit buffers each having a switch array to perform the fine-control scans.
20 . A method comprising:
receiving an input signal from a signal path mixed with an interference signal from a clock path;
implementing a phase interpolator (PI) in the clock path to generate multiple phases of a clock signal;
sampling the input signal and the interference signal based on a timing rotated in the phases generated by the PI in every cycle;
providing an ADC digital output based on a sampled input signal and a sampled interference at each of the phases;
detecting the sampled interference by demultiplexing the ADC digital output and canceling at least partially a component of the interference signal in each demultiplexed path using a digital adaptive loop to calibrate the sampled interference;
generating an analog cancellation signal based on a calibration loop using control parameters determined in the digital adaptive loop; and
injecting the analog cancellation signal into the signal path for at least canceling a part of the interference signal.