Noise In Diodes Research Articles

Deep Learning Calibration of the High-Frequency Airborne Microwave and Millimeter-Wave Radiometer (HAMMR) Instrument

Calibration plays an important role in improving the accuracy of the microwave and millimeter-wave radiometric measurements. Several calibration techniques have been used in radiometers including external calibration targets, vicarious sources, and internal calibrators such as noise diodes or matched reference load. A new calibration technique based on deep learning has recently been developed to calibrate microwave and millimeter-wave radiometers. The deep-learning calibrator has been previously demonstrated on a computer noise-wave modeled Dicke-switching radiometer. This article applies the new deep-learning calibration technique for the calibration of the high-frequency airborne microwave and millimeter-wave radiometer (HAMMR) instrument. A deep-learning neural network model is built to calibrate the 2014 West Coast Flight Campaign antenna temperature measurements of the HAMMR. The deep-learning calibrator antenna temperature estimates are obtained from the radiometric measurements. The deep-learning calibration results are compared with the existing conventional calibration techniques used in HAMMR 2014 field campaign. The results have shown that the deep-learning calibrator is in agreement with the conventional calibration techniques. In this article, it is demonstrated that the deep-learning calibrator can be employed for calibrating the radiometers with high accuracy.

Low-Frequency Excess Noise Ratio Approximation for Avalanche Noise Diodes

This letter deals with microwave noise diodes in avalanche regime. Starting from the model proposed by Hines and Gliden in 1966, the asymptotic excess noise ratio (ENR) expression is derived for $\omega \rightarrow 0$ . The developed theory is then validated against ENR measurements of three noise diodes already published in the literature. The agreement between theory and measurements is good and the obtained formula also predicts the $1/I_{0}$ behavior of the ENR at low frequencies. This study is relevant because it simplifies the experimental determination of the average time between two ionizations (the Hines $\tau _{x}$ model parameter) by means of low-frequency noise measurements only.

Millimeter-Wave Noise Source Development on SiGe BiCMOS 55-nm Technology for Applications up to 260 GHz

This paper describes the development and characterization of a millimeter-wave (mmW) integrated noise source development on silicon technology for applications up to 260 GHz. The developed integrated noise source is based on p-n and Schottky junction in series, realized on the SiGe BiCMOS 55-nm technology from STMicroelectronics. Biased in the avalanche regime, this integrated diode noise source achieves a tunable excess noise ratio (ENR) ranged between 0 dB and 15 dB, in the 130–260-GHz frequency range. In order to highlight the usefulness of the integrated noise source, the noise figure of two amplifiers was measured: the first one is an integrated low-noise amplifier (LNA) operating in the D-band (130–170 GHz) while the second one is packaged and operates from 220 to 260 GHz. Due to its ability to be naturally integrated on silicon, this noise source features a strong interest to carry out high-frequency in situ noise characterization of advanced Si CMOS or BiCMOS technologies in the mmW range.

Noise characteristics of a 750-MHz electronically tunable resonator for electron paramagnetic resonance spectroscopy

This paper describes an experimental investigation of the noise characteristics of a 750-MHz electronically tunable resonator for electron paramagnetic resonance (EPR) spectroscopy. The RF noise of the tunable resonator and its influence on the baseline noise of an EPR spectrum were systematically measured, considering both the noise of varactor diodes used in the impedance matching network of the resonator and noise from the ambient environment. The influence of magnetic field modulation and its amplitude on the baseline noise of the EPR spectrum was also measured. The tunable resonator itself increased the noise level of the spectral baseline of a home-built 750-MHz continuous-wave (CW) EPR spectrometer. A significant decrease in the noise level of the EPR spectral baseline was demonstrated by replacing the varactor diodes in the matching network by a trimmer capacitor, which led to a 6.1-fold improvement in EPR spectrum signal-to-noise ratio.

Effect of Electron Irradiation with an Energy of 0.9 MeV on the I–V Characteristics and Low-Frequency Noise in 4H–SiC pin Diodes

It is established experimentally that noticeable changes in the I–V characteristics and low-frequency noise in 4H-SiC pin diodes irradiated by electrons with an energy of 0.9 MeV are observed after doses of Φ ≥ 1.4 × 1015 cm–2. The currents in the forward and reverse branches of the I–V characteristics vary nonmonotonically at voltages lower than 2 V with increasing dose, which is explained by the interaction between the excited electronic subsystem and metastable defects. In this case, a steady increase in the ideality factor and the series resistance of diodes in the region of exponential growth of the I–V characteristics at voltages exceeding 2 V is observed. The reliable operation of microwave devices with low-noise 4H-SiC pin diodes under conditions of electron irradiation is possible up to a cumulative dose of Φ ≤ 1015 cm–2. In microwave devices, the level of low-frequency noise in which is irrelevant but the stabile regime of parameters is of importance, the dose can be increased to Φ ≈ 8 × 1015 cm–2.

Current Noise and Efficiency Droop of Light-Emitting Diodes in Defect-Assisted Carrier Tunneling from an InGaN/GaN Quantum Well

The current dependences of the spectral noise density and quantum efficiency in green and blue light-emitting diodes with InGaN/GaN quantum wells (QWs) are measured. It is shown that the noise level greatly increases at high currents at which there is a quantum efficiency droop. The mechanism by which the current noise is formed is associated with hopping transport via the deep states of color centers in GaN across the n barrier of an InGaN/GaN QW. The source of the noise is the hopping resistance of the space-charge region, which limits the current of thermally activated electrons into the QW. The efficiency droop and the increase in noise level are attributed to a change in the electric-field direction near the QW at high injection levels and to an increase in the tunneling leakage of holes from the QW. It is shown that the experimental frequency-related noise spectra having the shape of a Lorentzian spectrum at the working currents are related to the frequency of hopping between deep centers near the InGaN/GaN QW and to Maxwell relaxation in the space-charge region.

VESPA-22: a ground-based microwave spectrometer for long-term measurements of polar stratospheric water vapor

Abstract. The new ground-based 22 GHz spectrometer, VESPA-22 (water Vapor Emission Spectrometer for Polar Atmosphere at 22 GHz) measures the 22.23 GHz water vapor emission line with a bandwidth of 500 MHz and a frequency resolution of 31 kHz. The integration time for a measurement ranges from 6 to 24 h, depending on season and weather conditions. Water vapor spectra are collected using the beam-switching technique. VESPA-22 is designed to operate automatically with little maintenance; it employs an uncooled front-end characterized by a receiver temperature of about 180 K and its quasi-optical system presents a full width at half maximum of 3.5∘. Every 30 min VESPA-22 measures also the sky opacity using the tipping curve technique. The instrument calibration is performed automatically by a noise diode; the emission temperature of this element is estimated twice an hour by observing alternatively a black body at ambient temperature and the sky at an elevation of 60∘. The retrieved profiles obtained inverting 24 h integration spectra present a sensitivity larger than 0.8 from about 25 to 75 km of altitude during winter and from about 30 to 65 km during summer, a vertical resolution from about 12 to 23 km (depending on altitude), and an overall 1σ uncertainty lower than 7 % up to 60 km altitude and rapidly increasing to 20 % at 75 km. In July 2016, VESPA-22 was installed at the Thule High Arctic Atmospheric Observatory located at Thule Air Base (76.5∘ N, 68.8∘ W), Greenland, and it has been operating almost continuously since then. The VESPA-22 water vapor mixing ratio vertical profiles discussed in this work are obtained from 24 h averaged spectra and are compared with version 4.2 of concurrent Aura/Microwave Limb Sounder (MLS) water vapor vertical profiles. In the sensitivity range of VESPA-22 retrievals, the intercomparison from July 2016 to July 2017 between VESPA-22 dataset and Aura/MLS dataset convolved with VESPA-22 averaging kernels shows an average difference within 1.4 % up to 60 km altitude and increasing to about 6 % (0.2 ppmv) at 72 km.

Electrical and noise properties of proton irradiated 4H-SiC Schottky diodes

The current voltage characteristics and the low-frequency noise in high voltage 4H-SiC junction barrier Schottky diodes irradiated with high energy (15 MeV) protons were studied at different temperatures and irradiation doses Φ from 3 × 1012 cm−2 to 1 × 1014 cm−2. Irradiation led to the increase of the base resistance and the appearance of slow relaxation processes at small, V ≤ 0.2 V, and at rather high, V ≥ 2 V, forward voltages. The characteristic times of these relaxation processes ranged from ∼1 μs to 103 s. The exponential part of the current-voltage characteristic was only weakly affected by irradiation. The temperature dependence of the base resistance changed exponentially with temperature with activation energy Ea ∼ 0.6 eV, indicating that the Z1/2 level plays a dominant role in this process. The temperature increase also led to the increase of the ideality factor from 1.05 at 25 °C to 1.1 at 172 °C. At elevated temperatures and high forward voltages V > 2–4 V, the current voltage characteristics tend to be super-linear. It is concluded that at high voltages, the space charge limited current of majority carriers (electrons) and hole injection from the p-n regions play an important role in the formation of the current voltage characteristic. The frequency dependences of noise spectral density S of proton irradiated Schottky diodes have the unusual form of S ∼ 1/f 0.5.

Blind Detection for SPAD-Based Underwater VLC System Under P–G Mixed Noise Model

There is Poisson slot noise generated by the single photon avalanche diode (SPAD) and Gaussian thermal noise generated by the transimpedance amplifier, respectively, if an analog SPAD detector is applied in the visible light communication (VLC) system. In this letter, for the long distance SPAD-based underwater VLC system, a fast blind multiple-symbol detection (MSD) algorithm is developed under the pure Poisson noise model. And then, a blind MSD algorithm based on generalized maximum-likelihood rule under the Poisson-Gaussian (P-G) mixed noise model is proposed. A generalized Anscombe transform (GAT) is employed to make the P-G mixed noise model as an equivalent additive white Gaussian noise model, then an equivalent minimum Euclidean distance criterion is presented to formulate the optimization problem. Simulation results show that our blind MSD scheme can be identical to the performance under a GAT-based detector with perfect channel state information.

Independence between intensity and phase noise of superluminescent diodes in the low-frequency domain.

We theoretically and experimentally demonstrate a method for measuring the phase and intensity noise and their correlation in superluminescent diodes. A Michelson interferometer containing strongly unbalanced paths has been developed to measure the noise. By the spectral analysis of the photocurrents in detectors, the intensity noise is about twice the value of the phase noise in the superluminescent diode. The more interesting result we obtained is the experimental evidence that the intensity noise and the phase noise are mutually independent. The correlation coefficient of the intensity noise and the phase noise fluctuates between -0.08 and 0, which shows scarcely any sign of amplitude-phase noise correlation. The results offer a basic premise for the analysis of broadband light sources.

ENR Compensation of a Noise Source Using Calibration Coefficients With Variation of the Ambient Temperature

The excess noise ratio (ENR) of a noise source is largely dependent on the ambient temperature variation. In this paper, we discuss a method to compensate for the ENR of a noise source with respect to ambient temperature variations. From the measured quantities of the receiver and noise source from the setup, calibration coefficients of the noise source are extracted according to the relationship between bias voltage at the noise diode, the ENR, and the physical temperature of noise diode in the noise source by means of a least square estimation. From the result, the ENR of the noise source is compensated by the bias voltage at the noise diode controlled by a microcontroller and a digital-to-analog converter in the noise source. The compensated ENR variation is 0.167 dB for 1.4 dB ENR at 5.4 GHz in an ambient temperature range of 290–320 K. Specifically, the calibrated noise source shows the characteristics of 0.0016 dB/° C in a short ambient temperature range of 310–320 K. The time stability is about 0.007 dB/h for 1.4 dB ENR at 5.4 GHz. The uncertainty is evaluated in the experimental results, and the critical uncertainty contribution is confirmed by reading the power from a spectrum analyzer.

Reduction of NEP variations for terahertz detectors using Schottky barrier diodes in CMOS

Variations of low-frequency noise including flicker and Lorentzian spectra are the dominant source of variation of noise equivalent power (NEP) for terahertz detectors using diode-connected N-type MOS (NMOS) transistors. The low-frequency noise of Schottky diodes fabricated in the same CMOS process as the NMOS detectors are dominated by generation and recombination noise. At 1 MHz modulation frequency, the noise of Schottky barrier diodes (SBDs) and its variation are ∼2× lower than those of diode-connected NMOS transistors. It should be possible to reduce the variation of NEP by ∼2× using Schottky diode detectors modulated at 1 MHz.

Effect of high energy electron irradiation on low frequency noise in 4H-SiC Schottky diodes

The low-frequency noise in high voltage Ni/4H-SiC Schottky diodes irradiated with high energy (0.9 MeV) electrons was studied in the frequency range from 1 Hz to 50 kHz, temperature interval 295–410 K, and irradiation dose Φ from 0.2 × 1016 cm−2 to 7 × 1016 cm−2. The noise amplitude was found monotonically increasing with the irradiation dose. With the irradiation dose increase, the noise spectra on the linear part of the current voltage characteristic transform from the 1/f noise to the generation recombination noise of at least two trap levels. One of these levels can be classified as Z1/2 with the capture cross section determined from the noise measurements to be ∼10−15 cm2.

System calibration method for Fourier ptychographic microscopy

Fourier ptychographic microscopy (FPM) is a recently proposed computational imaging technique with both high-resolution and wide field of view. In current FPM imaging platforms, systematic error sources come from aberrations, light-emitting diode (LED) intensity fluctuation, parameter imperfections, and noise, all of which may severely corrupt the reconstruction results with similar artifacts. Therefore, it would be unlikely to distinguish the dominating error from these degraded reconstructions without any preknowledge. In addition, systematic error is generally a mixture of various error sources in the real situation, and it cannot be separated due to their mutual restriction and conversion. To this end, we report a system calibration procedure, termed SC-FPM, to calibrate the mixed systematic errors simultaneously from an overall perspective, based on the simulated annealing algorithm, the LED intensity correction method, the nonlinear regression process, and the adaptive step-size strategy, which involves the evaluation of an error metric at each iteration step, followed by the re-estimation of accurate parameters. The performance achieved both in simulations and experiments demonstrates that the proposed method outperforms other state-of-the-art algorithms. The reported system calibration scheme improves the robustness of FPM, relaxes the experiment conditions, and does not require any preknowledge, which makes the FPM more pragmatic.

Characterization of zero-bias microwave diode power detectors at cryogenic temperature.

We present the characterization of commercial tunnel diode low-level microwave power detectors at room and cryogenic temperatures. The sensitivity as well as the output voltage noise of the tunnel diodes is measured as functions of the applied microwave power. We highlight strong variations of the diode characteristics when the applied microwave power is higher than a few microwatts. For a diode operating at 4 K, the differential gain increases from 1000 V/W to about 4500 V/W when the power passes from -30 dBm to -20 dBm. The diode white noise floor is equivalent to a Noise Equivalent Power of 0.8 pW/Hz and 8 pW/Hz at 4 K and 300 K, respectively. Its flicker noise is equivalent to a relative amplitude noise power spectral density Sα(1 Hz) = - 120 dB/Hz at 4 K. Flicker noise is 10 dB higher at room temperature.

Various Techniques to Overcome Noise in Dynamic CMOS Logic

The advent of dynamic logic especially domino logic has made the use of dynamic circuits very wide for the implementation of low power VLSI circuits. Dynamic logic style is becoming the designers' choice these days because it has very fast speed and occupies very small area. In this paper we have used various techniques based on domino logic to overcome noise. Each technique has its merits and demerits. Out of these techniques mentioned below we have taken two widely used techniques in domino logic, conditional keeper technique and diode footed domino. We calculated their noise margins at different values of supply voltage. We have done simulations in 90 nm technology. After calculations we found both techniques show fairly good noise immunity but diode footed domino gave better results.

Analysis of origin of measured 1/f noise in high-power semiconductor laser diodes far below threshold current

The 1/f noise is measured under the bias one tenth the threshold current of the InGaAs quantum well high-power semiconductor laser diodes (LDs). The noise origin is analyzed using the current and voltage 1/f noise and dynamic resistance characteristics. Then the relationship between the noise and the internal defect is analyzed according to the differences of LDs in the noise intensity and the fluctuation near the initial electrical derivative peak. The result shows that with currents 0.13mA–1mA, the dynamic resistance of the LDs is in the magnitude of hundreds of ohms, when the changing rates of both the noise intensity and the resistance reflect the typical features of the active region, while with currents 8mA–32mA, the dynamic resistance drops under 10Ω and its changing rate slows down, when the 1/f noise intensity trend shows the features of the contact resistance. Moreover, the electrical derivative of LDs with weaker noise fluctuates milder and has more conspicuous initial peaks, while the electrical derivative of other LDs fluctuates acuter and hardly shows distinct initial peaks. The results indicate that the 1/f noise from the active region can be measured under bias currents far lower than the threshold currents of the LDs, and it can indicate the defects in the active region and further the reliability of the device.

Assessing Calibration Stability Using the Global Precipitation Measurement (GPM) Microwave Imager (GMI) Noise Diodes

With rising demand for smaller, lower mass microwave instruments, internal calibration using noise diodes is becoming increasingly more attractive for space-borne radiometer applications. Since noise diodes can exhibit on-orbit excess temperature drift, internally calibrated systems typically require vicarious on-orbit recharacterization. The GMI is the first instrument of its kind to include both internal (noise diodes) and external (hot load/cold sky) calibration systems. The dual-calibration system provides the unprecedented capability to directly measure transient behaviors in the hot load, cold sky view, and receiver nonlinearity. Furthermore, the behavior of the noise diodes can be directly evaluated, which may shed light on improvements to internal calibration for future missions. This paper directly examines the behavior of the GMI noise diodes using the hot load and cold sky views for the first 6 months of operations. Two of the seven channels with noise diodes have exhibited on-orbit noise diode excess temperature drift of about 1 K. The other noise diodes have remained exceptionally stable. The noise diodes are used to evaluate transient behaviors in the GMI hot load, cold sky view, and nonlinearity. The hot-load brightness temperature variation due to gradients is re-evaluated and shown to be smaller at the lower frequencies than at preflight calibration. Radio frequency interference (RFI) in the cold view is evaluated using the noise diode backup calibration. The on-orbit nonlinearity is trended over the first 6 months and shown to be stable over that time period.

GROMOS-C, a novel ground-based microwave radiometer for ozone measurement campaigns

Abstract. Stratospheric ozone is of major interest as it absorbs most harmful UV radiation from the sun, allowing life on Earth. Ground-based microwave remote sensing is the only method that allows for the measurement of ozone profiles up to the mesopause, over 24 hours and under different weather conditions with high time resolution. In this paper a novel ground-based microwave radiometer is presented. It is called GROMOS-C (GRound based Ozone MOnitoring System for Campaigns), and it has been designed to measure the vertical profile of ozone distribution in the middle atmosphere by observing ozone emission spectra at a frequency of 110.836 GHz. The instrument is designed in a compact way which makes it transportable and suitable for outdoor use in campaigns, an advantageous feature that is lacking in present day ozone radiometers. It is operated through remote control. GROMOS-C is a total power radiometer which uses a pre-amplified heterodyne receiver, and a digital fast Fourier transform spectrometer for the spectral analysis. Among its main new features, the incorporation of different calibration loads stands out; this includes a noise diode and a new type of blackbody target specifically designed for this instrument, based on Peltier elements. The calibration scheme does not depend on the use of liquid nitrogen; therefore GROMOS-C can be operated at remote places with no maintenance requirements. In addition, the instrument can be switched in frequency to observe the CO line at 115 GHz. A description of the main characteristics of GROMOS-C is included in this paper, as well as the results of a first campaign at the High Altitude Research Station at Jungfraujoch (HFSJ), Switzerland. The validation is performed by comparison of the retrieved profiles against equivalent profiles from MLS (Microwave Limb Sounding) satellite data, ECMWF (European Centre for Medium-Range Weather Forecast) model data, as well as our nearby NDACC (Network for the Detection of Atmospheric Composition Change) ozone radiometer measuring at Bern.

Low intensity noise and narrow line-width diode laser light at 540 nm

We present a convenient method to generate high quality single-frequency green light at a wavelength of 540 nm. It consists of a noise suppressed external cavity diode laser at a wavelength of 1080 nm by optical filtering and resonant optical feedback, and a frequency doubling of the fundamental light with an a-cut KTP crystal. Highly efficient conversion is realized by type II non-critical phase matching. A stable single-frequency operation with a maximum power of about 20 mW is performed for more than 3 h. Both the intensity noise and line-width reach the level of a monolithic nonplanar ring laser, which is well known for its extraordinarily narrow line-width and extremely low noise among available single-frequency operating lasers.