Zhaolin Sun

Joint Blind Calibration for Mixed Mismatches in Two-Channel Time-Interleaved ADCs

To further enhance the dynamic performance of time-interleaved analog-to-digital converters (TI-ADCs), both linear and nonlinear mismatches should be estimated and compensated for. This paper introduces a method for joint calibration of several types of linear and nonlinear mismatch errors in two-channel TI-ADCs. To demonstrate the generality of this method, we take different scenarios into account, including static and dynamic mixed mismatch models. The proposed method utilizes a normalized least-mean square (N-LMS) algorithm as well as a certain low degree of oversampling for the overall converter to estimate and compensate for the mixed mismatch errors. The calibration performance and computational complexity are investigated and evaluated through simulations.

Comparison of total variation algorithms for electrical impedance tomography

The applications of total variation (TV) algorithms for electrical impedance tomography (EIT) have been investigated. The use of the TV regularisation technique helps to preserve discontinuities in reconstruction, such as the boundaries of perturbations and sharp changes in conductivity, which are unintentionally smoothed by traditional l2 norm regularisation. However, the non-differentiability of TV regularisation has led to the use of different algorithms. Recent advances in TV algorithms such as the primal dual interior point method (PDIPM), the linearised alternating direction method of multipliers (LADMM) and the spilt Bregman (SB) method have all been demonstrated successful EIT applications, but no direct comparison of the techniques has been made. Their noise performance, spatial resolution and convergence rate applied to time difference EIT were studied in simulations on 2D cylindrical meshes with different noise levels, 2D cylindrical tank and 3D anatomically head-shaped phantoms containing vegetable material with complex conductivity. LADMM had the fastest calculation speed but worst resolution due to the exclusion of the second-derivative; PDIPM reconstructed the sharpest change in conductivity but with lower contrast than SB; SB had a faster convergence rate than PDIPM and the lowest image errors.

Digital estimation and compensation method for nonlinearity mismatches in time-interleaved analog-to-digital converters

Channel mismatches in time-interleaved analog-to-digital converters (TIADCs) typically result in significant degradation of the ADCs dynamic performance. Offset, gain, and timing mismatches have been widely investigated whereas nonlinearity mismatches have not. In this work, we analyze the influence of nonlinearity mismatches by using a polynomial model. As a cost measure we use the signal-to-noise and distortion ratio (SNDR) and then derive a compact formula describing the dependency on nonlinearity mismatches. Based on the spectral characteristics of the TIADCs, we propose a foreground estimation method and a compensation method using a cascaded structure of adders and multipliers. Through behavioral-level simulations, we prove the validity of the derivations and demonstrate that the proposed estimation and compensation method can bring a considerable amount of improvement in the combined TIADCs dynamic performance. The proposed method is efficient assuming that a smooth approximation of the nonlinearity mismatches is sufficient.

Estimation method for nonlinearity mismatch in time-interleaved analog-to-digital converters

Channel mismatches of time-interleaved analog-to-digital converters (TIADC) would result in significant decline of dynamic performance, especially in signal-to-noise and distortion ratio (SNDR) and spurious-free dynamic range (SFDR). However, as one kind of the channel mismatches, nonlinearity mismatch has not been widely investigated. In this paper, we analyze the characteristics of nonlinearity mismatch and its influence on TIADCs dynamic performance by using polynomial model. A foreground estimation method is proposed and evaluated. The simulation results demonstrate that the proposed method can perform fine estimation accuracy. Furthermore, we investigate the relationship between the estimation accuracy and the sample length, and the result is helpful to configure an appropriate sample length according to different performance requirements.

Reconfigurable Bioimpedance Emulation System for Electrical Impedance Tomography System Validation

This paper presents a novel bioimpedance emulation method designed for electrical impedance tomography system validation. The proposed method can emulate the impedance frequency characteristics of various biological samples from user configurations. The bioimpedance emulation system is realized in a hardware prototype comprising current sensing circuitry, voltage generating circuitry, a USB controller and a field-programmable gate array (FPGA) for reconfigurable digital control of emulated impedance. Experimental validation shows that the emulation system exhibits good accuracy ( > 97% at 1 kOhm magnitude) in the frequency range 1 kHz to 1 MHz. The digitally configurability offers advantages in flexibility, repeatability, and cost-efficient compared to more traditional approaches, simplifying the validation process of electrical impedance tomography systems.

Impact of active areas on electrical characteristics of TiO 2 based solid-state memristors

In this study, we explore the impact of active areas on electrical characteristics of practical TiO2 based memristors. Initially, it is experimentally demonstrated that high resistive state is independent of active areas, while low resistive state is in proportion to the dimensions of active cells. We then argue that these observations could stem from the filamentary formation and rupture within the TiO2 active cores. Finally, we investigate the dependence of I-V characteristics on active cell size and present measured results that are in good agreement with theoretical analysis.

A high-efficiency real-time digital signal averager for time-of-flight mass spectrometry

RATIONALE Analog-to-digital converter (ADC)-based acquisition systems are widely applied in time-of-flight mass spectrometers (TOFMS) due to their ability to record the signal intensity of all ions within the same pulse. However, the acquisition system raises the requirement for data throughput, along with increasing the conversion rate and resolution of the ADC. It is therefore of considerable interest to develop a high-performance real-time acquisition system, which can relieve the limitation of data throughput. METHODS We present in this work a high-efficiency real-time digital signal averager, consisting of a signal conditioner, a data conversion module and a signal processing module. Two optimization strategies are implemented using field programmable gate arrays (FPGAs) to enhance the efficiency of the real-time processing. A pipeline procedure is used to reduce the time consumption of the accumulation strategy. To realize continuous data transfer, a high-efficiency transmission strategy is developed, based on a ping-pong procedure. RESULTS The digital signal averager features good responsiveness, analog bandwidth and dynamic performance. The optimal effective number of bits reaches 6.7 bits. For a 32 µs record length, the averager can realize 100% efficiency with an extraction frequency below 31.23 kHz by modifying the number of accumulation steps. In unit time, the averager yields superior signal-to-noise ratio (SNR) compared with data accumulation in a computer. CONCLUSIONS The digital signal averager is combined with a vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). The efficiency of the real-time processing is tested by analyzing the volatile organic compounds (VOCs) from ordinary printed materials. In these experiments, 22 kinds of compounds are detected, and the dynamic range exceeds 3 orders of magnitude.

High Speed Real-Time Data Acquisition System Based on Solid-State Storage Technique

This paper presented a high speed data acquisition system for real-time appLication. The hardware of system mainly consists of data acquisition, distribution and storage section. A 3Gsps ultra high-speed ADC is appLied in acquisition section. In distribution section, the original data stream will be distributed into four streams. Each data stream will be stored into one soLid-state storage card which is composed of NAND flash array. In aspect of software, implementation methods of DDR3-based FIFO and NAND flash controller were introduced in detail. System evaluation results show that system achieved high bandwidth (up to 3.0GB/s) and good SNR (up to 45dB).

Blind calibration of nonlinearity mismatch errors in two-channel time-interleaved ADCs

To preserve the effective resolution of the individual converters in time-interleaved analog-to-digital converters (TIADCs), channel mismatches should be carefully corrected. In this paper, the proposed method is concentrated on achieving adaptive blind calibration for nonlinearity mismatches in two-channel TIADCs. It utilizes a least-mean square (LMS) algorithm as well as a polynomial-represented nonlinearity model. We assume a certain degree of oversampling for the overall converter to estimate and compensate for the mismatch errors. The calibration accuracy and convergence rate are investigated and evaluated through behavioral-level simulations.

Dual RAID: A scheme for high reliable all flash array

Flash-based solid state disks (SSDs) are replacing hard disk drives owing to its high performance and low energy consumption. For both high reliability and large capacity, redundant array of independent disks (RAID) is commonly used in storage system. In all flash arrays, the HDDs in RAID are substituted by SSDs and it gains improvements in bandwidth and IOPS (Input/output Operations per Second) by leaps and bounds owing to SSDs high performance. However, the error mode of SSD is different from HDD. The uncorrectable page errors in SSD are a great threat especially when a disk fails. For high reliability, we proposed a Dual-RAID scheme to protect data at disk level and block level respectively. To correct the disk failure, the proposed scheme adopts RAID-5 between disks. For recovering uncorrectable page errors, a redundant array of independent NANDs (RAIN) scheme is applied to SSD by exploiting its multi-channel structure. Although the redundancy overhead of the proposed scheme is about the same as RAID-6, the dual-RAID scheme achieves better performance and higher reliability. The experiment shows that the proposed scheme improves performance 35% on totally random trace in comparison to RAID 6 scheme.