Gain Calibration Research Articles

Bayesian self-calibration and imaging in very long baseline interferometry

Context. Self-calibration methods with the CLEAN algorithm have been widely employed in very long baseline interferometry (VLBI) data processing in order to correct antenna-based amplitude and phase corruptions present in the data. However, human interaction during the conventional CLEAN self-calibration process can impose a strong effective prior, which in turn may produce artifacts within the final image and hinder the reproducibility of final results. Aims. In this work, we aim to demonstrate a combined self-calibration and imaging method for VLBI data in a Bayesian inference framework. The method corrects for amplitude and phase gains for each antenna and polarization mode by inferring the temporal correlation of the gain solutions. Methods. We use Stokes I data of M87 taken with the Very Long Baseline Array (VLBA) at43 GHz, pre-calibrated using the rPICARD CASA-based pipeline. For antenna-based gain calibration and imaging, we use the Bayesian imaging software resolve. To estimate gain and image uncertainties, we use a variational inference method. Results. We obtain a high-resolution M87 Stokes I image at 43 GHz in conjunction with antenna-based gain solutions using our Bayesian self-calibration and imaging method. The core with counter-jet structure is better resolved, and extended jet emission is better described compared to the CLEAN reconstruction. Furthermore, uncertainty estimation of the image and antenna-based gains allows us to quantify the reliability of the result. Conclusions. Our Bayesian self-calibration and imaging method is able to reconstruct robust and reproducible Stokes I images and gain solutions with uncertainty estimation by taking into account the uncertainty information in the data.

X-ray spectral performance of the Sony IMX290 CMOS sensor near Fano limit after a per-pixel gain calibration

X-ray spectral performance of the Sony IMX290 CMOS sensor near Fano limit after a per-pixel gain calibration

A Fully Synthesizable Fractional-N Digital Phase-Locked Loop with a Calibrated Dual-Referenced Interpolating Time-to-Digital Converter to Compensate for Process–Voltage–Temperature Variations

This paper presents advancements in the performance of digital phase-locked loop (DPLL)s, with a special focus on addressing the issue of required gain calibration in the time-to-digital converter (TDC) within phase-domain DPLL structures. Phase-domain DPLLs are preferred for their simplicity in implementation and for eliminating the delta–sigma modulator (DSM) noise inherent in conventional fractional-N designs. However, this advantage is countered by the critical need to calibrate the gain of the TDC. The previously proposed dual-interpolated TDC(DI-TDC) was proposed as a solution to this problem, but strong spurs were still generated due to the TDC resolution, which easily became non-uniform due to PVT variation, degrading performance. To overcome these problems, this work proposes a DPLL with a new calibration system that ensures consistent TDC resolution matching the period of the digitally controlled oscillator (DCO) and operating in both the foreground and background, thereby maintaining consistent performance despite PVT variations. This study proposes a DPLL using a calibrated dual-interpolated TDC that effectively compensates for PVT variations and improves the stability and performance of the DPLL. The PLL was fabricated in a 28-nm CMOS process with an active area of only 0.019 mm2, achieving an integrated phase noise (IPN) performance of −17.5 dBc, integrated from 10 kHz to 10 MHz at a PLL output of 570 MHz and −20.5 dBc at 1.1 GHz. This PLL operates within an output frequency range of 475 MHz to 1.1 GHz. Under typical operating conditions, it consumes only 930 µW with a 1.0 V supply.

An ADPLL-Based GFSK Modulator with Two-Point Modulation for IoT Applications.

To establish ubiquitous and energy-efficient wireless sensor networks (WSNs), short-range Internet of Things (IoT) devices require Bluetooth low energy (BLE) technology, which functions at 2.4 GHz. This study presents a novel approach as follows: a fully integrated all-digital phase-locked loop (ADPLL)-based Gaussian frequency shift keying (GFSK) modulator incorporating two-point modulation (TPM). The modulator aims to enhance the efficiency of BLE communication in these networks. The design includes a time-to-digital converter (TDC) with the following three key features to improve linearity and time resolution: fast settling time, low dropout regulators (LDOs) that adapt to process, voltage, and temperature (PVT) variations, and interpolation assisted by an analog-to-digital converter (ADC). It features a digital controlled oscillator (DCO) with two key enhancements as follows: ΔΣ modulator dithering and hierarchical capacitive banks, which expand the frequency tuning range and improve linearity, and an integrated, fast-converging least-mean-square (LMS) algorithm for DCO gain calibration, which ensures compliance with BLE 5.0 stable modulation index (SMI) requirements. Implemented in a 28 nm CMOS process, occupying an active area of 0.33 mm2, the modulator demonstrates a wide frequency tuning range of from 2.21 to 2.58 GHz, in-band phase noise of -102.1 dBc/Hz, and FSK error of 1.42% while consuming 1.6 mW.

Wideband N-Path-Based Phased-Array Receiver With Gain and Phase Mismatch Calibration

Wideband N-Path-Based Phased-Array Receiver With Gain and Phase Mismatch Calibration

Implementation of an ionization chamber array for linear accelerator monthly dosimetry QA.

The IC Profiler (ICP) manufactured by Sun Nuclear Corporation (SNC) is an ionization chamber (IC) array used for linear accelerator dosimetry measurements. Previous work characterized response of the ICP under various conditions, but there is limited work of its implementation into monthly QA measurement procedures. This work quantifies ICP accuracy and variables that affect accuracy for beam output measurements, and demonstrates feasibility of using the ICP for all recommended monthly dosimetry measurements. A total of 1985 output measurements on six Varian TrueBeam and Edge linear accelerators were performed using three ICP with quad wedges (QWs) and were compared with conventional IC measurements. The accuracy of the ICP for beam output was characterized as the difference between the ICP and IC. Variables that affect ICP accuracy, including gain settings, calibrations, and template baselining as well as machine or energy-specific bias were investigated. Measurements of profile constancy, energy, dose rate constancy, wedge factors, and gating were performed. The initially observed mean output difference between the ICP and IC was 0.16% (0.61%). When gain settings were optimized, the output difference accuracy improved to -0.02% (0.38%). The output accuracy of the ICP was not dependent on array, dose, temperature and pressure calibrations, or template baselining. Statistically, ICP output accuracy was dependent on machine and beam energy, but clinically, all measurements fell within 0.5% of unity. ICP measurements of energy, dose rate constancy, and wedge factors matched passing results with conventional IC in water measurements. Gating and beam profile constancy measurements demonstrated good stability using the ICP. Finally, monthly dosimetry QA using ICP was completed in an average of 33 min compared to 66 min using the IC. This work demonstrated the feasibility and efficiency of using the ICP, with specific considerations, as a measurement device for dosimetric linear accelerator monthly QA.

Sensitivity of a Lumped-Capacitance Building Thermal Modelling Approach for Energy-Market-Scale Flexibility Studies

Despite all the literature on building energy management, building-stock-scale models depicting its impact for energy-market-scale optimisation models are lacking. To address this shortcoming, an open-source tool called ArchetypeBuildingModel.jl has been developed for aggregating building-stock-level data into simplified lumped-capacitance thermal models compatible with existing open-source energy-system modelling frameworks. This paper aims to demonstrate the feasibility of these simplified thermal models by comparing their performance against dedicated building simulation software, as well as examining their sensitivity to key modelling and parameter assumptions. Modelling and parameter assumptions comparable to the existing literature achieved an acceptable performance according to ASHRAE Guideline 14 across all tested buildings and nodal configurations. The most robust performance was achieved with a period of variations above 13 days and interior node depth between 0.1 and 0.2 for structural thermal mass calibrations, and with external shading coefficients between 0.6 and 1.0 and solar heat gain convective fractions between 0.4 and 0.6 for solar heat gain calibrations. Furthermore, three-plus-node lumped-capacitance thermal models are recommended when modelling buildings with structures varying in terms of thermal mass. Nevertheless, the ArchetypeBuildingModel.jl performance was found to be robust against uncertain key parameter assumptions, making it plausible for energy-market-scale applications.

An interstage gain calibration technique for pipelined ADCs exploiting complementary dithering and calibration windows detector

An interstage gain calibration technique for pipelined ADCs exploiting complementary dithering and calibration windows detector

Current Measurement Gain Compensation Using High-Frequency Signal Injection in Dual Three-Phase PMSM Systems

To online compensate the scaling errors in current measurement caused by incorrect calibration, temperature, aging, and noise, this paper proposes a new solution based on high-frequency (HF) carrier voltage injection in dual three phase permanent magnet synchronous machines. The relationship between the measured HF currents and scaling errors is derived. It shows that the amplitudes of the HF currents are proportional to the scaling errors, based on which three HF current control loops are subsequently designed to eliminate the measured HF currents and compensate the scaling errors. The designed HF controller are independent from the main current and torque regulators, and thus, it can be used for initial scaling gain calibration or periodically used during normal machine operation. Different from general three phase machine systems, the generated HF current components only exist in z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> subspace, and thus, no extra torque ripples will be produced. Experimental results validate the proposed control algorithm.

Blind Array Calibration of Mutual Coupling, Phase, and Gain for Automotive Radar

Blind Array Calibration of Mutual Coupling, Phase, and Gain for Automotive Radar

Design and performance of a gain calibration system for the POLARBEAR-2a receiver system at the Simons Array cosmic microwave background experiment

Design and performance of a gain calibration system for the POLARBEAR-2a receiver system at the Simons Array cosmic microwave background experiment

A Low-Complexity In-Run Modal Frequency Tuning Method for MEMS Disk Gyroscopes Without Gain Calibration and Phase Shifting

A Low-Complexity In-Run Modal Frequency Tuning Method for MEMS Disk Gyroscopes Without Gain Calibration and Phase Shifting

Joint Blind Calibration of Unknown Gain and Mutual Coupling Errors for MWC System

Joint Blind Calibration of Unknown Gain and Mutual Coupling Errors for MWC System

A laserball calibration device for the SNO+ scintillator phase

Located 2 km underground in SNOLAB, Sudbury, Canada, SNO+ is a large scale liquid scintillator experiment that primarily aims to search for neutrinoless double beta decay. Whilst SNO+ has light and radioactive calibration sources external to the inner volume, an internally deployed optical source is necessary for the full characterization of the detector model. A laser diffuser ball developed for SNO has previously demonstrated to be an effective optical calibration device for both SNO and SNO+ water phase. Since the introduction of liquid scintillator for SNO+, the material compatibility, cleanliness, and radiopurity requirements of any materials in contact with the internal medium have increased. Improving on the original SNO laserball design, a new laserball calibration device has been developed for the SNO+ scintillator phase with the goal of measuring the optical properties of the detector and performing routine PMT gain and timing calibrations. Simulations have been written to model the diffusion properties to optimise optical and temporal performance for calibration. Prototype laserballs have been built and characterised, demonstrating sub-ns timing resolution and a quasi-isotropic light distribution.

JPSS-3 / 4 VIIRS response versus scan angle characterization and performance

Scientific studies of the Earth’s climate increasingly rely on high-quality satellite observations. The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor onboard a series of satellites [Suomi National Polar-orbiting Partnership (SNPP) and Joint Polar-orbiting Satellite System 1–4 (JPSS-1–JPSS-4)] that generate scientific data from land, ocean, and atmosphere used in these climate models. Providing quality scientific data from space-borne sensors requires the instruments to be well-calibrated. While much of the calibration can be maintained on-orbit, some aspects of the calibration can best be measured prior to launch. One VIIRS parameter that needs to be measured pre-launch is the response versus scan angle (RVS). The RVS measures the relative change in the reflectance of the scanning optics as a function of the angle of incidence. With the RVS, the gain calibration measured on-orbit can be transferred to any scan angle. The JPSS-3 and JPSS-4 instruments have undergone ground testing including the RVS measurements, which is the subject of this work. Results indicate that the measurements are comparable to previous VIIRS builds and are expected to contribute to the generation of high-quality science data once JPSS-3 and JPSS-4 are on-orbit.

First M87 Event Horizon Telescope Results. IX. Detection of Near-horizon Circular Polarization

Event Horizon Telescope (EHT) observations have revealed a bright ring of emission around the supermassive black hole at the center of the M87 galaxy. EHT images in linear polarization have further identified a coherent spiral pattern around the black hole, produced from ordered magnetic fields threading the emitting plasma. Here we present the first analysis of circular polarization using EHT data, acquired in 2017, which can potentially provide additional insights into the magnetic fields and plasma composition near the black hole. Interferometric closure quantities provide convincing evidence for the presence of circularly polarized emission on event-horizon scales. We produce images of the circular polarization using both traditional and newly developed methods. All methods find a moderate level of resolved circular polarization across the image (〈∣v∣〉 < 3.7%), consistent with the low image-integrated circular polarization fraction measured by the Atacama Large Millimeter/submillimeter Array (∣v int∣ < 1%). Despite this broad agreement, the methods show substantial variation in the morphology of the circularly polarized emission, indicating that our conclusions are strongly dependent on the imaging assumptions because of the limited baseline coverage, uncertain telescope gain calibration, and weakly polarized signal. We include this upper limit in an updated comparison to general relativistic magnetohydrodynamic simulation models. This analysis reinforces the previously reported preference for magnetically arrested accretion flow models. We find that most simulations naturally produce a low level of circular polarization consistent with our upper limit and that Faraday conversion is likely the dominant production mechanism for circular polarization at 230 GHz in M87*.

Qualification of the X-ray spectral performance of the DEPFET pixels of the DSSC imager

The first DEPFET module (128 x 512 pixels) of the DSSC pixel detector, designed for user experiments at the European XFEL, has been fully instrumented and an experimental campaign has been carried out with X-ray lines to qualify the main performance figures and to collect calibration data. X-ray spectra fitting has been optimized with consideration to the main sources of systematic errors to achieve gain calibration within 1% accuracy, which is a key issue for its successful operation at the European XFEL. The most important result is the equivalent noise charge of 16 el rms on average. This shows the potential of the DEPFET-based pixel to reach single-photon imaging down to the lowest photon energy (0.25 keV) at 4.5 MHz frame frequency that can be extrapolated at camera level with high confidence.

A 4 GHz FLL-less fast-locking sampling PLL with gain-boosted sampling phase-frequency detector in 28 nm CMOS

This paper presents a sampling PLL (SPLL) using a gain-boosted sampling phase-frequency detector (SPFD) to suppress in-band phase noise. The implementation of the SPFD eliminates the need for a frequency-locked loop (FLL). Additionally, a cycle slipping elimination (CSE) technique is incorporated into the SPFD to enhance the locking speed of the SPLL. The proposed SPFD achieves phase detection gain multiplication by sampling both rising and falling slopes simultaneously, effectively reducing the noise contribution of building blocks with low-pass characteristics without compromising the linear phase detection range. To enhance the reliability of the SPFD, a phase detection gain calibration strategy is proposed, involving a replica capacitor array and a successive approximation algorithm, ensuring a consistent phase detection gain. Moreover, by integrating capacitive coupled noise circulating (CCNC) technique and 2nd harmonic control (F2) technique, a low noise CCNC–F2 VCO is introduced to further suppress out-of-band phase noise of the SPLL. Implemented using a 28 nm CMOS process, the SPLL employing the SPFD and CCNC–F2 VCO achieves a fitted RMS jitter of 61 fs integrated from 10 kHz to 100 MHz at an operating frequency of 4 GHz. The SPLL consumes 20.1 mW, occupies an area of 0.26 mm2 and achieves a jitter figure-of-merit (FoM) of −251.3 dB.

An improved PVT-Robust floating inverter dynamic amplifier for noise-shaping SAR ADCs

The floating inverter dynamic amplifier (FIDA) is a power-efficient, open-loop, and dynamic amplifier without requiring any output common-mode feedback (CMFB) circuit. It is appropriate for low-power applications. However, its gain is not robust over process, voltage, and temperature (PVT) variations. In this work, a simple, low power, and low noise method is proposed to solve this problem. The proposed method controls the amplification time window of the FIDA to be proportional to its time constant. Based on the FIDA gain formula, this technique stabilizes the gain over PVT changes. The proposed PVT-robust FIDA is designed at the circuit level using 0.18 µm TSMC CMOS technology with Cadence Virtuoso tool. According to the post-layout simulation results of a sample design, the gain of the amplifier is 29.4 with 51.3 µW power consumption from a 1.2 V supply voltage. The maximum gain variation over PVT changes is reduced from 49.6% to 9.8% using the proposed gain calibration technique.

In-orbit performance of LE onboard Insight-HXMT in the first 5 years

The low-energy X-ray telescope (LE) is a main instrument of the Insight-HXMT mission and consists of 96 swept charge devices covering the 1–10 keV energy band. The energy gain and resolution are continuously calibrated by analyzing Cassiopeia A (Cas A) and blank sky data, while the effective areas are also calibrated with the observations of the Crab Nebula. In this paper, we present the evolution of the in-orbit performances of LE in the first 5 years since launch. The Insight-HXMT data analysis software package (HXMTDAS) is utilized to extract the spectra of Cas A, blank sky, and Crab Nebula using different good time interval selections. We fit a model with a power-law continuum and several Gaussian lines to different ranges of Cas A and blank sky spectra to get peak energies of their lines through xspec. After updating the energy gain calibration in CALibration DataBase (CALDB), we rerun the Cas A data to obtain the energy resolution. An empirical function is used to modify the simulated effective areas so that the background-subtracted spectrum of the Crab Nebula can best match the standard model of the Crab Nebula. The energy gain, resolution, and effective areas are calibrated every month. The corresponding calibration results are duly updated in CALDB, which can be downloaded and used for the analysis of Insight-HXMT data. Simultaneous observations with NuSTAR and NICER can also be used to verify our derived results. LE is a well-calibrated X-ray telescope working in 1–10 keV band. The uncertainty of LE gain is less than 20 eV in 2–9 keV band, and the uncertainty of LE resolution is less than 15 eV. The systematic errors of LE, compared to the model of the Crab Nebula, are lower than 1.5% in 1–10 keV.