Charna R. Parkey

A non-destructive high-voltage low-energy intermittent fault location system

The practical implementation of a high voltage/low energy portable tool is discussed to address the need for intermittent fault diagnostic solutions. Recent results from aircraft testing are reported, safety validation is discussed and future system upgrades are addressed to support ease of use as a field diagnostic tool.

Modeling of jitter and its effects on time interleaved ADC conversion

Post analog-to-digital conversion correction is an active area of research in both academia and industry due to the high potential of positive impact in areas like Synthetic Instrumentation (SI), Software Defined Radio (SDR), RADAR, etc. This paper introduces a high fidelity Simulink™ based behavioral error model for time-interleaved analog-to-digital converters (TI-ADCs) to facilitate development of efficient post conversion correction algorithms for TI-ADCs. Theoretically TI-ADCs offer a technologically feasible and cost effective solution to the digitization of wide bandwidth analog signals. The contribution of the error model described in this paper solves a key obstacle in economical research and development in this area. In addition to the error sources associated with integrated high performance analog to digital converters ADCs, mismatched error sources affect the performance of time interleaved configurations.

Simulink modeling of analog to digital converters for post conversion correction development and evaluation

Theoretically time interleaved analog-to-digital converters (TI-ADCs) offer a technologically feasible and cost effective solution to the digitization of wide bandwidth analog signals. In addition to the error sources associated with integrated high performance analog to digital converters (ADCs) and the exaggerated impact of certain error sources, mismatched error sources exist. The topic of post conversion correction is an active area of research in both academia and industry due to the high potential of positive impact in areas like test instrumentation, software defined radio, radar, etc. A key stumbling block to cost effective research and development is the availability of high fidelity, high level simulations of realistic error performance of data converters. This paper describes a high fidelity, high level Simulink™ based M TI-ADC model capable of facilitating cost effective development of efficient post conversion correction algorithms. Four TI-ADCs are interleaved as an example and errors effects are discussed. A survey of published adaptive correction methods to be evaluated against this model is presented.

Time interleaved analog to digital converters: Tutorial 44

This tutorial has addressed the structure and basics of TIADCs, including errors, implementation concerns and possible solutions. While the past few years have shown a sharp increase in patents and industry participation, academic research around the world is still ongoing to improve performance while reducing computational complexity, particularly in the area of nonlinear mismatch correction and scalable correction schemes to handle massively interleaved structures. Reduction in this complexity is critical to reduce the cost of digital logic in post conversion correction structures as well as the power consumption of the overall TIADC system through the use of smaller, simpler post conversion components. TIADCs are currently used in the field for test and measurement as well as communications and other applications.

Analyzing artifacts in the time domain waveform to locate wire faults

Wire integrity is a growing concern with aging vehicles, especially high vibration variants like helicopters, tiltrotor aircraft, and many mobile ground weapons systems. Wiring failures on these systems present a growing safety concern and can lead to loss of equipment and life. This paper presents a novel adaptive time domain reflectometry (TDR) algorithm to analyze artifacts found on the reflected time domain waveform of a high-voltage, low-energy pulse transmitted down wires with uncontrolled or controlled impedances. This method allows for detection of intermittent and hard faults. Most time domain reflectometers (TDRs) are used to measure cable lengths and distances to hard opens or shorts. Existing technology has extended TDR measurement capability to intermittent faults. Current detection methods for intermittent faults require an experienced engineer to interpret the returned measurement and waveform to confirm its accuracy. To make this technology more accessible, the repeatability and accuracy of the automated measurements need to be improved. The following method improves the unadjusted accuracy by three times. This paper reviews the theory of TDR and presents implementation and results of the proposed algorithm on real-world data.

Linearized adaptation of non-linear post conversion correction for TIADCs: a behavioral model study

Current and emerging applications need high speed and high resolution analog to digital converters (ADCs). Direct conversation for radar, communication, measurement systems as well as lower speed higher resolution applications such as medical imaging could benefit from the use of time interleaved analog to digital converters (TIADCs). This paper presents the implementation and results of the proposed adaptive linear combination of non-linear filters for post conversion correction of TIADCs applied to a behavioral TIADC model. Results show that the channelized correction scheme can suppress linear and nonlinear mismatch spurs by a significant amount, 30dB in the 2TIADC case, without the need for known system parameters.

A method of combining intermittent arc fault technologies

Intermittent wire faults can be caused by harsh environments, handling or simply aging of the sheathing. These types of faults are difficult to isolate due to the intermittent nature. Recent advances in intermittent fault detection have provided the aerospace and defense industry new methods to test aging aircraft wiring. In particular the use of Low Energy High Voltage (LEHV) methods and Spread Spectrum Time Domain Reflectometry (SSTDR) has shown promise in locating intermittent faults in a variety of situations. These technologies have distinct advantages which best serve the industry in a combined package. This paper presents a novel method of combining these technologies in a portable fashion to solve the growing need for intermittent fault detection.

Linearized adaptation of non-linear post conversion correction for TIADCs: A behavorial model study

Current and emerging applications need high speed and high resolution analog to digital converters (ADCs). Direct conversion for radar, communications, measurement systems as well as lower speed higher resolution applications such as medical imaging could benefit from the use of time interleaved analog to digital converters (TIADCs). This paper presents the implementation and results of the proposed adaptive linear combination of non-linear filters for post conversion correction of TIADCs applied to a behavioral TIADC model. Results show that the channelized correction scheme can suppress linear and nonlinear mismatch spurs by a significant amount, 30dB in the 2TIADC case, without the need for known system parameters.

Cumulant characterizations of ADC error sources with applications to Time Interleaved ADCs

The problem of characterizing transfer functions of Analog to Digital Converters (ADC) for use in compensation of Time Interleaved Analog to Digital Converters (TIADC) is ubiquitous in the area of mismatch correction algorithms. Identifying, classifying, and quantifying the presence of errors in ADCs and TIADCs is fundamental in the pursuit of correcting these errors. This problem, characterization of error effects, is investigated through calculation of higher order cumulants on the error signals of each type of system. The concept of cumulant calculation and interpretation is presented and applied to varying error environments and input signals.

Cumulant statistical adaptation of non-linear post conversion correction for TI-ADCs

Practical implementations of post conversion correction of time interleaved analog to digital converters (TI-ADCs) is of particular interest to the test and measurement community due to the demand for large instantaneous bandwidths and high dynamic ranges required by many fields. Ideally TIADCs allow for an increased sampling rate while maintaining the performance of the individual converters. In practice this is harder to achieve. Ultra wideband communications as well as direct conversion applications in RADAR also benefit from practical implementations of TI-ADCs. One such method proposed in this paper is based upon the work that was presented last year by the authors at Autotest 14 where an adaptive linear combination of nonlinear filters placed in the channels can ideally suppress the mismatches when driven by an ideal error signal. Here it is proposed that the structure can be driven by an approximate cumulant statistical adaptation these results are compared to an implementation of a non-ideal error signal generated using interpolation techniques. Various cumulants are discussed from the 1st to 8th order. These statistics are calculated using Boxcar FIR filter moving average approximations in place of averages over the entire dataset. A single channel is used as a reference and is interpolated to generate the reference samples for the second channel. This paper presents the implementation and results of the practical design applied to a behavioral TIADC model. The model is based upon off the shelf performance of 14 bit 80MSPS converters that suggest the performance of the intended implemented system and has been presented in prior works by the authors, allowing for evaluation of the new correction method in a realistic scenario. Results show that the cumulant based channelized correction scheme can suppress linear and nonlinear mismatch spurs by a significant amount, on average 35 dB up to ideal suppression in the sinusoidal input case. When a wideband QPSK input is used during adaptation, between 6dB and 20dB suppression is achieved. Design considerations will be presented including how to choose initial conditions, step size, the cumulant statistic used and adaptation time for implementations in the 2 and 4 TIADC case.