Abstract: A digital signal processing method is for enhancing fidelity of equivalent-time waveform measurements. The method includes receiving a digitized equivalent-time waveform of a repeating signal under test (SUT), applying a low-pass filter to the digitized equivalent-time waveform to obtain a smoothed waveform, generating a residual waveform by subtracting the smoothed waveform from the digitized equivalent-time waveform, estimating contributions of multiple noise sources in the residual waveform using a regression model, computing target noise and jitter values by removing known intrinsic contributions, and reconstructing a corrected waveform by combining the smoothed waveform with a scaled version of the residual waveform, wherein the scaling is based on the target noise source contributions.

Abstract: A test system implemented method removes intrinsic noise from a waveform representation of a repeating signal under test (SUT). The method includes obtaining an oversampled equivalent-time waveform representation of the repeating SUT. The method further includes obtaining a time-domain representation of a combined noise of the equivalent-time waveform above the deterministic maximum frequency by applying the equivalent-time waveform to a high-pass filter. The method further includes determining a standard deviation of the time-domain representation of the combined noise, and determining a correction factor ? in accordance with the standard deviation of the digitizer noise, and the standard deviation of the time-domain representation of the combined noise.

Abstract: A test system implemented method removes intrinsic noise from a waveform representation of a repeating signal under test (SUT). The method includes obtaining an oversampled equivalent-time waveform representation of the repeating SUT. The method further includes obtaining a time-domain representation of a combined noise of the equivalent-time waveform above the deterministic maximum frequency by applying the equivalent-time waveform to a high-pass filter. The method further includes determining a standard deviation of the time-domain representation of the combined noise, and determining a correction factor ? in accordance with the standard deviation of the digitizer noise, and the standard deviation of the time-domain representation of the combined noise.

Abstract: A controller includes a memory, a processor, and a first interface to a clock recovery unit that provides a recovered clock. When executed by the processor, instructions from the memory cause the controller to: instruct, via the first interface, the clock recovery unit at a first loop bandwidth to provide the recovered clock to a signal sampler; instruct, via the first interface, the clock recovery unit at a second loop bandwidth wider than the first loop bandwidth, to provide the recovered clock to the signal sampler; compare measurements from the signal sampler at the first loop bandwidth to measurements from the signal sampler at the second loop bandwidth; and instruct, via the first interface, the clock recovery unit at a third loop bandwidth to provide the recovered clock to the signal sampler applying adjustments based on comparing the measurements.

Abstract: A controller includes a memory, a processor, and a first interface to a clock recovery unit that provides a recovered clock. When executed by the processor, instructions from the memory cause the controller to: instruct, via the first interface, the clock recovery unit at a first loop bandwidth to provide the recovered clock to a signal sampler; instruct, via the first interface, the clock recovery unit at a second loop bandwidth wider than the first loop bandwidth, to provide the recovered clock to the signal sampler; compare measurements from the signal sampler at the first loop bandwidth to measurements from the signal sampler at the second loop bandwidth; and instruct, via the first interface, the clock recovery unit at a third loop bandwidth to provide the recovered clock to the signal sampler applying adjustments based on comparing the measurements.

Abstract: A method and system provide for measuring a repeating waveform of a SUT. The method includes repeatedly sampling first and second copies of the SUT to provide first SUT waveforms including first noise introduced by a first digitizer and second SUT waveforms including second noise introduced by a second digitizer; pairing the first and second SUT waveforms to provide corresponding pairs of first and second digital samples; organizing the pairs of first and second digital samples into groups of sample pairs corresponding to sampling times; for each group, calculating a covariance of the first and second digital samples to estimate a signal variance of the SUT, and scaling the first and second digital samples to preserve a mean of the group while adjusting a variance of the group to match the estimated signal variance of the SUT at the corresponding sampling time; and reassembling the groups into the SUT waveform.

Abstract: A method and system are provided for reducing noise in a time domain waveform of a signal under test (SUT). The method includes performing cross-correlation of multiple first complex signals and multiple second complex signals, respectively, from the SUT to provide multiple cross-correlated signals, respectively, where the cross-correlated signals have amplitude components and no phase components from the SUT, and where the first and second complex signals include uncorrelated noise, respectively. The method further includes determining an average of the cross-correlated signals to provide an average cross-correlated signal with reduced uncorrelated noise; obtaining a representative phase component from one of the first complex signals or the second complex signals; and combining the representative phase component with the average cross-correlated signal to provide a representative complex signal corresponding to the SUT with reduced uncorrelated noise.

Abstract: A method of filtering a signal sampled by a sampler, for example, in an equivalent time oscilloscope includes applying a correction to an actual frequency response of the sampler, with respect to a reference frequency response, to a first frequency range of the sampled signal, and transitioning across a second frequency range of the sampled signal from the correction applied to the first frequency range to no correction of the actual frequency response of the sampler, the second frequency range being higher than the first frequency range. The method further includes compensating in a third frequency range of the sampled signal for excess gain incurred while applying the correction and transitioning from the correction to no correction in the first and second frequency ranges, respectively, so that statistics of asynchronous components of the sampled signal are preserved, the third frequency range being higher than the second frequency range.

Abstract: A direct determination equalizer system (“DDES”) for compensating for the deterministic effects of a transmission channel and a data source is disclosed. The DDES may include an equalizer having equalizer-tap coefficients, a cross-correlator configured to receive the first sampled signal and an ideal signal and in response produce a cross-correlated signal, and a processor in signal communication with the equalizer and the cross-correlator. The equalizer is configured to receive a first sampled signal and in response produce an equalized output data signal sequence and the processor is configured to determine the equalizer-tap coefficients from the cross-correlated signal.