Proposed Calibration Techniques Research Articles

Black-Box Diagnosis and Calibration on GAN Intra-Mode Collapse: A Pilot Study

Generative adversarial networks (GANs) nowadays are capable of producing images of incredible realism. Two concerns raised are whether the state-of-the-art GAN’s learned distribution still suffers from mode collapse and what to do if so. Existing diversity tests of samples from GANs are usually conducted qualitatively on a small scale and/or depend on the access to original training data as well as the trained model parameters. This article explores GAN intra-mode collapse and calibrates that in a novel black-box setting: access to neither training data nor the trained model parameters is assumed. The new setting is practically demanded yet rarely explored and significantly more challenging. As a first stab, we devise a set of statistical tools based on sampling that can visualize, quantify, and rectify intra-mode collapse . We demonstrate the effectiveness of our proposed diagnosis and calibration techniques, via extensive simulations and experiments, on unconditional GAN image generation (e.g., face and vehicle). Our study reveals that the intra-mode collapse is still a prevailing problem in state-of-the-art GANs and the mode collapse is diagnosable and calibratable in black-box settings. Our codes are available at https://github.com/VITA-Group/BlackBoxGANCollapse .

A Biomedical Sensor System With Stochastic A/D Conversion and Error Correction by Machine Learning

This paper presents a high-precision biomedical sensor system with a novel analog-frontend (AFE) IC and error correction by machine learning. The AFE IC embeds an analog-to-digital converter (ADC) architecture called successive stochastic approximation ADC. The proposed ADC integrates a stochastic flash ADC (SF-ADC) into a successive approximation register ADC (SAR-ADC) to enhance its resolution. The SF-ADC is also used as a digitally controlled variable threshold comparator to provide error correction of the SAR-ADC. The proposed system also calibrates the ADC error using the machine learning algorithm on an external PC without additional power dissipation at a sensor node. Due to the flexibility of the system, the design complexity of an AFE IC can be relaxed by using these techniques. The target resolution is 18 bits, and the target bandwidth (without digital low-pass filter) is about 5 kHz to deal with several types of biopotential signals. The design is fabricated in a 130-nm CMOS process and operates at 1.2-V supply. The fabricated ADC achieves the SNDR of 88 dB at a sampling frequency of 250 kHz by using the proposed calibration techniques. Due to the high-resolution ADC, the input-referred noise is 2.52 μV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> with a gain of 28.5 dB.

A multilaboratory comparison of calibration accuracy and the performance of external references in analytical ultracentrifugation.

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.

Transfer-Function-Based Calibration of Sparse EEG Systems for Brain Source Localization

This paper describes a transfer-function-based calibration technique for a sparse electroencephalography (EEG) source localization system. The forward solution and synthetic EEG signals are generated using the Brainstorm software. Various forms of calibration errors have been defined and induced on the nominal manifold, with different magnitudes. Two transfer-function-based calibration techniques are presented and the improvement brought about using these methods are compared against the results from benchmark scenarios. The performance of the proposed calibration techniques has been quantified in terms of the localization errors in the recovered sources before and after calibrating the system. Simulations suggest that in the presence of calibration errors, the proposed technique is capable of reducing the localization error as well as the number of falsely recovered sources.

A Reconfigurable 50-Mb/s-1 Gb/s Pulse Compression Radar Signal Processor With Offset Calibration in 90-nm CMOS

This paper presents a reconfigurable mixed-signal-processing circuit for high-speed pulse compression radar (PCR). Mixed-signal design techniques incorporate calibration and adaptation to improve the performance of a PCR receiver. Adaptive bandwidth PCR is an important feature for maximizing the dynamic range of a low-power radar system. The baseband signal processor includes a variable gain amplifier, 4-bit digital-to-analog converter, high-speed analog correlator, passive integrator, a 4-bit flash analog-to-digital converter, and a multi-range delay-locked loop. This proposed system is fabricated in 90-nm CMOS and can be configured to work from 50 Mb/s to 1 Gb/s with 2/3/5/7-bit Barker codes. The proposed calibration techniques improve the sidelobe reduction to 15.6 dB at 1 Gb/s. The total power consumption is 42 mW at the peak rate of 1 Gb/s for 15-cm range resolution.

Automatic 2-D LiDAR geometric calibration of installation bias

This paper proposes two estimation algorithms for the determination of the attitude installation matrix for 2-D light detection and ranging (LiDAR) systems on board unmanned aerial vehicles (UAVs). While a comparative calibration algorithm assumes the existence of a known calibration surface, an automatic calibration algorithm does not require any prior knowledge of the trajectories of the vehicle or the terrain where the calibration mission is performed. The proposed calibration algorithms rely on the minimization of the errors between the measured point cloud and a representation of the known calibration surface or, alternatively, the errors between several acquired point clouds, by comparing each measured point cloud with a surface representation of the others. The resulting optimization problems are addressed using two techniques: (i) nonlinear optimization, where the attitude installation rotation matrix is parameterized by the ZYX Euler angles, and (ii) optimization on Riemannian manifolds, enabling the estimation of the attitude installation matrix on the group of special orthogonal matrices SO(3). The proposed calibration techniques are extensively validated and compared using both simulated and experimental LiDAR data sets, demonstrating their accuracy and performance.

A study on machine calibration techniques

A coordinate measuring machine (CMM) with two linear axes and an articulated arm has been developed for on machine in situ measurement of just machined workpieces. Some techniques for calibrating the CMM parameters, such as the arm and stylus lengths, offsets, parallelism and squareness errors between axes, as well as zero positions of the articulated arm and stylus, have been worked out, which are essential for assuring high accuracy of the CMM. The effectiveness of the proposed calibration techniques has been proved by experiments and practice.

Digitally-Controlled Polarization-Forming Transmitting Antenna for Mobile Satellite Communication Systems

This paper presents a novel electrical polarization forming antenna for mobile satellite communication systems using linear polarization. To electrically form the desired polarization, it is necessary to excite the two orthogonal polarization antenna planes with appropriate weights. The proposed antenna uses digitally-based polarization and calibration functions to characterize the two RF paths. The calibration techniques used are critical to accurately forming the desired polarization. Proposed calibration techniques are very simple; the feedback signal consists of just amplitude levels. The proposals are validated by polarization forming measurements conducted on a fabricated antenna.

Automatic Camera-Based Microscope Calibration for a Telemicromanipulation System Using a Virtual Pattern

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In the context of virtualized-reality-based telemicromanipulation, this paper presents a visual calibration technique for an optical microscope coupled to a charge-coupled device (CCD) camera. The accuracy and flexibility of the proposed automatic virtual calibration method, based on parallel single-plane properties, are outlined. In contrast to standard approaches, a 3-D virtual calibration pattern is constructed using the micromanipulator tip with subpixel-order localization in the image frame. The proposed procedure leads to a linear system whose solution provides directly both the intrinsic and extrinsic parameters of the geometrical model. Computer simulations and real data have been used to test the proposed technique, and promising results have been obtained. Based on the proposed calibration techniques, a 3-D virtual microenvironment of the workspace is reconstructed through the real-time imaging of two perpendicular optical microscopes. Our method provides a flexible, easy-to-use technical alternative to the classical techniques used in micromanipulation systems. </para>

A Robust and Fast Digital Background Calibration Technique for Pipelined ADCs

This paper presents a background calibration scheme for pipelined analog-to-digital converters (ADCs) that is robust and has short calibration time. For a switched-capacitor (SC) pipeline stage, by splitting its input sampling capacitor, a random sequence can be injected into the ADC's signal path, and then calibration data can be extracted from the ADC's digital output without interrupting its normal conversion operation. Using an input-dependent scheme to generate the calibration random sequence, no additional signal range is required to accommodate the extra calibration signal. Furthermore, using random choppers to scramble signal can ensure that all necessary calibration data can be collected within a given time regardless of input conditions, resulting in a more robust ADC. A split-channel ADC architecture is proposed to reduce the calibration time. The split-channel ADC consists of two A/D channels that receive the same analog input but employ different random sequences for calibration. The calibration time can be greatly reduced by comparing the digital outputs from both channels and then removing the embedded perturbations before extracting the calibration data. The proposed calibration techniques are analyzed by using both theoretical formulation and system-level simulation.

CALIBRATED OPTION BOUNDS

This paper proposes a numerical approach for computing bounds for the arbitrage-free prices of an option when some options are available for trading. Convex duality reveals a close relationship with recently proposed calibration techniques and implied trees. Our approach is intimately related to the uncertain volatility model of Avellaneda, Levy and Parás, but it is more general in that it is not based on any particular form of the asset price process and does not require the seller's price of an option to be a differentiable function of the cash-flows of the option. Numerical tests on S&amp;P500 options demonstrate the accuracy and robustness of the proposed method.

저전류 측정을 위한 반도체 소자 특성 분석 시스템에서의 보상 기법

본 논문에서는 반도체 소자의 특성 분석을 위한 시스템에서 측정 회로에 의해 발생하는 오차를 감소시켜 측정 정밀도를 개선시키기 위한 보정 과정을 제안하였다. 또한 pA 수준의 저전류 측정을 위해서 누설 전류, 오프셋 전류와 같은 오차 전류를 감소시키기 위한 보상 기법을 제안하였다. 보정계수는 마이크로프로세서에 의해 보정 과정에서 수집된 데이터로부터 구해진다. 수집된 데이터를 최소 자승 오차법을 사용하여 다항식으로 근사하는 방법으로 보정 계수를 계산하고 저장한다. 측정 시에는 마이크로프로세서가 저장된 보정 계수를 사용하여 측정 오차를 교정하여 준다. 실험 결과에서 nA 이상의 전류를 측정할 경우 측정 오차가 0.02% 이하를 가지며 pA 수준의 저전류도 0.2% 정도의 오차로 측정 가능함을 확인하였다. In this paper, we proposed calibration techniques to improve measurement accuracy in the characteristic analysis system for semiconductor devices. Systematic errors can be reduced using proposed calibration techniques. Also, error current reduction procedures including leakage current and offset current are proposed to measure low-level current in pA level. Calibration parameters are calculated and stored by microprocessor using least-square fitting with measured sample data. During measurement time microprocessor corrects measured data using stored calibration parameters. Experimental results show that current measurement error above nA level is less than 0.02%. And they also show that current measurement in pA level can be performed with about 0.2% accuracy.

Theory &amp; Methods: Calibration of the estimators of variance

This investigation suggests new techniques to calibrate estimators of variance. Estimators of the variance of simple mean, ratio and regression estimators under different sampling schemes are shown to be special cases of the proposed calibration techniques. The approach has more practical use due to recent advances in programming techniques and computational speed. An empirical study has been carried out to address the properties of these proposed strategies.

Robust SOLT and alternative calibrations for four-sampler vector network analyzers

This paper assesses the accuracy of several proposed lumped-element calibration techniques for four-sampler vector network analyzers in the face of imperfectly defined standards. We find that these methods offer a wide range of accuracies, depending on the standards and how well they can be modeled. We introduce a new robust short-open-load-thru calibration that requires the same measurement and computational effort as traditional methods, but provides much better accuracy in transmission measurements and slightly better accuracy in reflection measurements.

Satellite altimeter calibration techniques

During the next five years several satellites carrying high accuracy radar altimeters are scheduled for launch. These include the European Space Agency ERS-1 satellite and the jointly sponsored NASA/CNES TOPEX/POSEIDON satellite. In-flight height calibration and height stability verification for both satellites are planned, and studies have been conducted to ascertain the calibration techniques which can most effectively satisfy the mission requirements. All of the proposed calibration techniques require at least one laser to provide the satellite height reference. For most techniques, only one laser in the calibration area is utilized; in this instance the satellite groundtrack must pass relatively close (within 20 km) to the laser site in order to obtain an orbit height uncertainty of less than one cm. The currently proposed calibration techniques for over-water calibration include: (1) tide gauge on a tower at-sea and a nearby laser; (2) laser and tide gauge on an island with offshore satellite pass and geoid tie between satellite groundtrack and laser, (3) tide gauge on a tower at-sea with satellite positioning from multiple lasers and a Global Positioning System (GPS) tie between the lasers and tide gauge; and (4) laser and tide gauge on a tower at-sea. Error budgets for these techniques have been developed based on state-of-the art laser tracking systems. For a single pass, these budgets have been found to have one sigma height uncertainties in the 2.8 to 4.9 cm range.