Low-noise Bias Research Articles

Optimization of MP2RAGE T1 mapping with radial view-ordering for deep brain stimulation targeting at 7 T MRI

PurposeDeep brain stimulation (DBS) is an effective treatment of various neurological disorders. Due to higher intrinsic signal, 7 T MRI can potentially improve delineation of DBS targets. However, the severe RF transmit field (B1+) inhomogeneity at 7 T can compromise the image contrast of traditional single-contrast sequences for DBS targeting, leading to sub-optimal target visualization. The Magnetization Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE)-based T1 mapping provides an alternative to the traditional single-contrast techniques by allowing retrospective synthesis of images at arbitrary inversion times to aid in visualization of various DBS targets. With this approach, optimization of sequence parameters to create T1 maps with low noise and low quantification bias is critical, as these characteristics directly affect the noise and uniformity of the synthetic images. In this work, we perform sequence optimization for MP2RAGE-based T1 mapping using a radial view-ordering technique to improve image quality, and demonstrate the clinical utility of T1 mapping approach for DBS targeting. MethodsWe first introduce a systematic sequence optimization framework for 7 T MP2RAGE T1 mapping by formulating it into a constrained, multi-dimensional optimization process considering the effect of B1+ inhomogeneity on image noise, T1 quantification bias, and image blurring. With this framework, we investigate the use of radial view-order approach for T1 mapping, in lieu of the conventional linear view-ordering. Bloch's equation-based simulations were performed to compare the T1 maps generated using different approaches. Images of healthy volunteer and patients were acquired on a clinical 7 T MRI scanner for validation and to demonstrate the utility of T1 mapping for DBS targeting. ResultsNumerical experiments demonstrated that the proposed framework allowed optimization of image SNR in T1 maps while controlling the quantification bias and image blurring, therefore facilitating the selection of optimal sequence parameters for visualizing DBS targets. The optimized sequence using radial view-ordering offered 40–60% noise reduction compared to the linear view-ordering. The improvement of SNR was confirmed in the in vivo examples. Clinical images showed that the synthetic images generated from the optimized T1 maps allowed clear visualization of DBS targets. ConclusionWe demonstrated the optimization of MP2RAGE T1 mapping with radial view-ordering technique for DBS targeting at 7 T and showed that the optimized sequence allows retrospective generation of synthetic inversion time images commonly utilized in DBS targeting, such as fast gray matter acquisition T1 inversion recovery (FGATIR) and edge-enhancing gradient echo (EDGE) sequences.

Simple and active magnetic-field stabilization for cold atom experiments.

Cold atom experiments usually need a controllable and low-noise bias magnetic field to provide a quantization axis. Most labs need home-made stabilization of the field according to the actual setup, as commercially available power supply cannot directly satisfy their requirements. Here, by measuring the field fluctuations and active feedback modulating current supply of the applied magnetic field, we successfully demonstrate a field of 10.58G with a stability to the level of 2.8 × 10-7 in a duration of 5min. The root mean square noise is reduced to 0.05 mG, compared to the noise of 1.3 mG without stabilization. The coherence time of the magnetic-field sensitive transition between the rubidium ground states F=1,mF=-1 and 1,0, as measured by Rabi oscillation, is extended to 19.2ms from the unstabilized value of 1.3ms. This result is long enough for most experiments on quantum simulation and precision measurement. As our system has no passive magnetic shielding and additional compensation coils, it is highly simple and compact to provide the stable magnetic field and would be adapted to various applications with cold atoms.

Characterization of self-heating in cryogenic high electron mobility transistors using Schottky thermometry

Cryogenic low-noise amplifiers based on high electron mobility transistors (HEMTs) are widely used in applications such as radio astronomy, deep space communications, and quantum computing. Consequently, the physical mechanisms governing the microwave noise figure are of practical interest. In particular, the magnitude of the contribution of thermal noise from the gate at cryogenic temperatures remains unclear owing to a lack of experimental measurements of thermal resistance under these conditions. Here, we report measurements of gate junction temperature and thermal resistance in a HEMT at cryogenic and room temperatures using Schottky thermometry. At temperatures ∼20 K, we observe a nonlinear trend of thermal resistance vs power that is consistent with heat dissipation by phonon radiation. Based on this finding, we consider heat transport by phonon radiation at the low-noise bias and liquid helium temperatures and estimate that the thermal noise from the gate is several times larger than previously assumed owing to self-heating. We conclude that without improvements in thermal management, self-heating results in a practical lower limit for microwave noise figure of HEMTs at cryogenic temperatures.

Calibration and stability of highly sensitive fibre based laser through relative intensity noise

This work is concerned with the characterization of the fiber based laser sensor by means of relative intensity noise (RIN). The characterization has been done by an electrical based measurement system, which has been accomplished by the implementation of an optical receiver setup. The optical receiver setup has been built by using commercially available low noise amplifier (LNA), Bias Tee, and fast photodiode (FPD). Besides the optical receiver setup designing, software in Labview has been built and implemented to enable easy and fast measurement of data from measurement instruments. Using the self assembled optical receiver and an electrical spectrum analyzer (ESA), optical fluctuation ’noise’ of the fiber based laser sensor has been measured. We have found good agreement between the measurement results taken by our measurement setup and costly Agilent RIN measurement setup. Also, average RIN over wide frequency range has been calculated and discussed for different operating states of the laser sensor. The results are applicable in the field of an optical sensor.

InAs Channel Inset Effects on the DC, RF, and Noise Properties of InP pHEMTs

GaInAs/InAs composite channels in InP-based pHEMTs enable wideband and/or low-noise performances because of their superior carrier transport properties. To date, the influence of the InAs inset design details on transistor performance has not been parametrized in the literature. We present a systematic study of the effects of the InAs channel inset thickness on transistor characteristics and cutoff frequencies versus temperature, and on the noise performance at 300 K. The epitaxial layer structures considered here incorporate 2 to 5-nm InAs insets in a fixed total composite channel thickness. All layers exhibit excellent electron mobilities (from 40 200 to 54 800 cm2/Vs at 77 K). Thicker InAs insets improve both the current gain cutoff frequency ( ${f}_{\text {T}}$ ) and the maximum oscillation frequency ( ${f}_{\text {MAX}}$ ). However, they also result in higher gate leakage currents and increased channel impact ionization. 50-nm gate length pHEMTs with a 5-nm InAs inset feature the highest simultaneous ${f}_{\text {T}} / {f}_{\text {MAX}} \ge {390}$ /675 (455/800) GHz at 300 (15) K for a low-noise bias but exhibit the poorest minimum noise figure ${NF}_{\text {MIN}}$ . Whereas higher ${f}_{\text {T}}$ (and/or ${f}_{\text {MAX}}$ ) values have traditionally been associated with improved noise performances, this is no longer the case.

Low Frequency Noise and Gate Bias Instability in Normally OFF AlGaN/GaN HEMTs

In this brief, traps-related dispersion phenomena are investigated on GaN/AlGaN MOS-high-electron mobility transistors. Pulsed $I$ – $V$ characteristics and low-frequency-noise measurements are the characterization vehicles used to get a direct insight of the device trap-states. By considering a set of ten samples, device-to-device fluctuation parameters extracted from trap-related measurements (1/ $f$ noise and gate bias instability) are systematically compared with conventional electrical parameters (threshold voltage and ON-current). Two separate trends are identified and ascribed to two different trap families.

Design of a Low Noise Bias Generator for Multi-band RF CMOS Transceiver

A low noise bias generator for RF CMOS transceiver is proposed and implemented. The bias generator consists of a bandgap reference(BGR) and a low dropout regulator(LDO). In RF transceiver, the bias blocks determining bias quantity and quality of the signal-processing circuits are separately placed near each signal block for noise performance and proper power dividing. Therefore, bias block design issues such as power consumption, noise and chip size should be considerd for multi-band RF CMOS transceiver which has various circuit blocks and chip area constraints. This paper describes a design procedure and techniques for a low noise bias generator. The proposed techniques allow good trade-off among chip size, noise and power consumption. The bias generator gives temperature compensated bandgap reference of 1.2V with mean temperature dependency of 5ppm/˚C for -25˚C to 75˚C. The LDO is able to drive max bias current of 15mA. The bias generator is implemented in a 0.18m RF CMOS technology with a size of 0.2×0.4mm2 and consumes a bandgap core current of 40A at 2.5V supply and works for a power supply down to 1.8V. Output noise level is below 30nV/√Hz at 100kHz. A CMOS VCO with the proposed bias generator has the phase noise difference of only 2.2dBc/Hz at 400kHz offset.

Characterization and Modeling of Cryogenic Ultralow-Noise InP HEMTs

Detailed S-parameter and noise characterization and modeling of ultralow-noise InP/InAlAs/InGaAs high-electron mobility transistors (InP HEMTs) optimized for operation at 10 K are presented. At the optimum low-noise bias at 10 K, the InP HEMT exhibited a 60% improvement in cutoff frequency <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fT</i> and a 100% improvement in dc transconductance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gm</i> compared with 300 K. A small-signal noise model was evaluated at different bias conditions at 10 and 300 K. The bias dependence of the minimum noise temperature at low-noise operation was modeled at 10 K. The temperature dependence of the threshold voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VT</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gm</i> , and gate-source and gate-drain capacitances <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cgs</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Cgd</i> indicated that the excellent cryogenic noise performance of optimized InP HEMTs is due to a higher degree of confinement in the carrier concentration closest to the gate at 10 K compared with 300 K. As a result, a fast depletion of the HEMT channel with respect to drain current <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Id</i> occurs under cryogenic operation.

An 8-W 250-MHz to 3-GHz Decade-Bandwidth Low-Noise GaN MMIC Feedback Amplifier With &gt; +51-dBm OIP3

This paper describes a GaN monolithic microwave integrated circuit (MMIC) cascode feedback amplifier design which achieves up to 8 W of output power and greater than +51 dBm OIP3 across a 250-3000-MHz decade bandwidth. The LNA also achieves 20 dB of flat-gain across the band. The design was fabricated with a 0.25-μm GaN HEMT technology with an fT ~ 50 GHz and a BVgd >; 60 V. A 40-V 750-mA high-bias LNA design achieves an OIP3 of 51.9 dBm, P1dB of 38.5 dBm, and NF ~ 3 dB at 2 GHz . A 40-V 500-mA medium-bias LNA design achieves a lower NF ~ 2.5 dB , an OIP3 of 48.4 dBm, and a P1dB of 36.8 dBm at the same frequency. At an optimum low-noise bias of 20 V and 300 mA, a NF ~ 0.96 dB, an OIP3 of 43.4 dBm, and a linear P1dB of ~32.2 dBm was also obtained. The combination of high OIP3 and low NF from these GaN MMIC LNA designs exceed that achieved by many state-of-the-art PHEMT, HBT, and HFET technologies for decade-BW MMIC amplifiers operating in the popular wireless and wire-line S- and C-band frequency ranges. The linear GaN LNA performance demonstrated here can enable new generations of software-defined and reconfigurable radios which require ultra-linearity over multiple octaves of bandwidth.

The EMIR multi-band mm-wave receiver for the IRAM 30-m telescope

Aims. The prime motivation of this project was to design and build a state-of-art mm-wave heterodyne receiver system to enhance the observing throughput of the IRAM 30-m radiotelescope. More specifically, the requirements were i) state-of-art noise performance for spectroscopic observations; ii) simultaneous dual polarization and dual-frequency observing; iii) coverage of the atmospheric transmission windows from 83 to 360 GHz; iv) compact footprint and minimal maintenance.Methods. Key elements for low noise performance of heterodyne mixers are the superconducting Niobium junctions, operating at ≃4 K. These junctions are embedded in carefully designed coupling structures; furthermore, since atmospheric radiation is a significant contributor to the system noise budget, all mixers are either sideband separating or sideband rejecting. To achieve low noise, it is also essential to maximize the coupling of the receiver to the astronomical source, and to minimize the coupling to thermal radiation from the ground-based environment; this is achieved through mirror optics that realize a wavelength-independent coupling to the telescope. A flexible configuration of mirrors and frequency selective surfaces permits various combinations of frequency bands, as well as dual-load radiometric calibration. Low noise intermediate frequency amplifiers and bias electronics also play an important role in the system performance.Results. The EMIR receiver in operation at the 30 m telescope offers four frequency bands: B1: 83−117 GHz, B2: 129−174 GHz, B3: 200−267 GHz, and B4: 260−360 GHz. In each band, the two orthogonal polarizations are observed simultaneously. Dual-band combinations B1/2 B1/3, and B2/4 are available. Bands 1 and 4 (also 3 as of Nov.-2011) feature sideband separation. In dual-band configuration, including sideband separation and polarization diplexing, up to eight IF channels are delivered to the spectrometers, totaling up to 64 GHz of signal bandwidth (of which 32 GHz can be transported and processed by spectrometers, status Nov.-2011). The EMIR receiver has been in continuous operation for more than two years and has allowed, through a qualitative jump in performance, observations not possible before, as shown by a few selected examples of astronomical results.

Parallel Poisson disk sampling with spectrum analysis on surfaces

The ability to place surface samples with Poisson disk distribution can benefit a variety of graphics applications. Such a distribution satisfies the blue noise property, i.e. lack of low frequency noise and structural bias in the Fourier power spectrum. While many techniques are available for sampling the plane, challenges remain for sampling arbitrary surfaces. In this paper, we present new methods for Poisson disk sampling with spectrum analysis on arbitrary manifold surfaces. Our first contribution is a parallel dart throwing algorithm that generates high-quality surface samples at interactive rates. It is flexible and can be extended to adaptive sampling given a user-specified radius field. Our second contribution is a new method for analyzing the spectral quality of surface samples. Using the spectral mesh basis derived from the discrete mesh Laplacian operator, we extend standard concepts in power spectrum analysis such as radial means and anisotropy to arbitrary manifold surfaces. This provides a way to directly evaluate the spectral distribution quality of surface samples without requiring mesh parameterization. Finally, we implement our Poisson disk sampling algorithm on the GPU, and demonstrate practical applications involving interactive sampling and texturing on arbitrary surfaces.

Highly programmable temperature compensated readout circuit for capacitive microaccelerometer

This paper describes a capacitive microaccelerometer system and readout circuit topology with a high programmability and a low temperature dependency. The MEMS sensing element is fabricated using the Sacrificial Bulk Micromachining (SBM) process and the Wafer Level Hermetic Packaging (WLHP) process, to achieve high reliability, low noise and low bias instability. The readout circuit exploits a highly programmable capacitive sensing architecture with an on-chip EEPROM in order to calibrate the output offset and the scale factor. The temperature compensated sub-circuits, including a bandgap reference, a current reference, and an oscillator, are designed to enhance the temperature characteristics. The supply voltage variations are compensated for by using an on-chip voltage regulator. The reverse voltage protection circuit is also designed to enhance the electrical reliability. After calibrating the scale factor and the offset by using the programmable circuits, the scale factor error and the offset error are compensated to 1.2%FSO and 3.3%FSO, respectively. The temperature coefficient of the offset is measured to be 43 ppm/°C in the temperature range from −40 °C to 125 °C. The bias instability and the noise equivalent resolution are measured to be in the range from 16.1 μg to 135.2 μg, and from 93.5 μ g/ Hz to 514.0 μ g/ Hz , respectively.

A Cool, Sub-0.2 dB Noise Figure GaN HEMT Power Amplifier With 2-Watt Output Power

This paper reports on a S-, C-band low-noise power amplifier (LNPA) which achieves a sub-0.2 dB noise figure (NF) over a multi-octave band and a saturated output power (Psat) of 2 W at a cool temperature of -30degC . The GaN MMIC is based on a 0.2 mum AlGaN/GaN-SiC HEMT technology with an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ~ 75 GHz. At a cool temperature of -30degC and a power bias of 15 V-400 mA, the MMIC achieves 0.25-0.45 dB average NF over a 2-8 GHz band and a linear P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> of 32.8 dBm ( ~ 2 W) with 25% power-added efficiency (PAE). At a medium bias of 12 V-200 mA, the amplifier achieves 0.1-0.2 dB average NF across the same band and a P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> of 32.2 dBm (1.66 W) with 35% PAE. The corresponding saturated output power is greater than 2 W. At a low noise bias of 5 V-200 mA, a remarkable 0.05-0.15 dB average NF is achieved with a P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> > 24 dBm and PAE ~ 33%. These results are believed to be the lowest NF ever reported for a multi-octave fully matched MMIC amplifier capable of > 2 W of output power.

Epitaxial Optimization of 130-nm Gate-Length InGaAs/InAlAs/InP HEMTs for Low-Noise Applications

The epitaxial structure of 130- nm gate-length InGaAs/InAlAs/InP high electron mobility transistors (HEMTs) has been studied in order to optimize the device performance when biased under low-noise conditions. Three essential epitaxial parameters have been varied: the In channel content ([In]: 53%, 70%, and 80%), the delta-doping concentration (delta: 3, 5, and 7 times 1012 cm-2), and the Schottky layer thickness (dSL: 9,11, and 13 nm). All HEMTs exhibited low gate-leakage current IG below 1 muA/mm at a low-noise bias, except dSL = 9 nm due to a too thin Schottky layer thickness. It was verified that the lowest noise figure NF was achieved when the square root of the drain-to-source current IDS over transconductance gm exhibited a minimum. A clear optimum for both dSl and delta was observed with respect to minimum noise figure NFmin. Increasing [In] only provided a slight reduction in N-Fmin. In contrast, the RF performance was much more affected by increasing [In]. The lowest NFmin was achieved with a delta doping of 5 times 1012 cm2 and a dSL of 11 nm.

A Stereo Multi-Rate Audio Front-End Suitable for Mobile Multimedia Applications

A flexible, high quality audio front-end integrated circuit with low power consumption is presented. Targeted for the world-wide (GSM) mobile communication system, it is capable of stereo and mono reception and transmission, supports narrow voice-band as well as wide voice-band modes, FM radio and MP3 stereo play-back. The front-end provides a low-noise bias voltage for microphones as well as hands-free buffers driving 8? loads in bridge tied load configuration and two earphone outputs for stereo. The front-end is highly area-efficient, occupying 1.92 mm2 in a 0.25-? m CMOS technology. Measured results show a maximum power consumption of 11.8 mW at 2.65 V analog and 1.65 V digital supply.

LANGEVIN APPROACH TO UNDERSTAND THE NOISE OF MICROWAVE TRANSISTORS

A Langevin approach to understand the noise of microwave devices is presented. The device is represented by its equivalent circuit with the internal noise sources included as stochastic processes. From the circuit network analysis, a stochastic integral equation for the output voltage is derived and from its power spectrum the noise figure as a function of the operating frequency is obtained. The theoretical results have been compared with experimental data obtained by the characterization of an HEMT transistor series (NE20283A, by NEC) from 6 to 18 GHz at a low noise bias point. The reported procedure exhibits good accuracy, within the typical uncertainty range of any experimental determination. The approach allows to extract all the information required for understanding the noise performance of the device without any restriction on the statistics of the noise sources. The results show the relevant noise phenomena from a new angle.

A low cost uncooled focal plane array test system

The commercial test equipments from Pulse Instruments, Lumitron and Electro Optical Industries Inc. are very expensive. So, we proposed a new method of very low cost test system for testing the non-uniformity and signal/noise (S/N) and other characteristics of the uncooled focal plane array (UFPA). It uses complex programmable logic device to generate the necessary pulse for the UFPA and the low noise low dropout micropower regulator to obtain the low noise bias. A proportional-integral-differential controlled thermal electrical cooler based on micro-processor unit stabilizes the UFPA. The National Instruments 6111E Data Acquisition Card is used to convert the analog output of UFPA into digital signal into computer. Its 12-bits conversion capability provides sufficient accuracy for evaluating the S/N ratio and non-uniformity of 128×128 pixels UFPA. Labview is used to analyze the signal. The instrument is fast and convenient to adapt the system to other types of UFPA. Further discussion is presented to determine factors that affect the accuracy of the tester.

The programmable front-end system for CUORICINO, an array of large-mass bolometers

We report on the front-end electronics designed for the readout of the CUORICINO experiment's array of 60 large-mass bolometers. The front end consists of a preamplifier and a bias system for the bolometer. A significant feature of our design is its capability for in situ DC characterization of each bolometer as a function of applied bias. The principal front-end operating parameters, low-noise bias selection, load resistor selection, offset compensation, and gain are remotely programmable.

Low-Noise Amperometric Detector for Use in Capillary Electrophoresis

A low noise amperometric detector suitable for capillary electrophoresis has been constructed from integrated operational amplifiers with low noise and low input bias current. It includes a potentiostat and a vertical wall-jet detection cell. The circuit design of the potentiostat, the construction of the detection cells, and methods for minimizing the noise are described. Performance tests of the detector were performed for the determination of catecholmines.

Low-Noise Bias Reliability of AlInAs/GaInAs Modulation-Doped Field Effect Transistors with Linearly Graded Low-Temperature Buffer Layers Grown on GaAs Substrates

The low-noise bias reliability of 0.1 µm T-gate Al0.48In0.52As/Ga0.47In0.53As modulation-doped field effect transistors (MODFETs), grown on GaAs was investigated. Al0.48In0.52As/Ga0.47In0.53As MODFETs were grown on mismatched GaAs substrates by the insertion of a compositionally linearly-graded low-temperature buffer (LGLTB) layer. Transmission electon microscopy (TEM) analysis of the layers indicates that the majority of the defects are confined to the buffer layer. Although the LGLTB layer is highly defective, there is no indication that the low-bias reliability of these devices is compromised. MODFETs with a LGLTB layer show reliability under high temperature operating life (HTOL) tests at a drain bias of 1 V and 200 mA/mm, comparable to reported MODFETs grown lattice-matched to InP. The extrapolated mean-time-to-failure (MTTF), based on the drift of the zero-gate bias current, Idss, at temperatures of 200 to 240°C, exceeds 106 h at a channel temperature of 125°C. The drift in Idss arises primarily from a positive shift in threshold voltage. The low-bias Rd degradation behavior of these devices is also similar to devices grown on InP.