Dominant Noise Contribution Research Articles

A hybrid amplifier topology for low‐noise direct‐coupled front ends

SummaryHybrid amplifiers combine discrete transistors with operational amplifiers (OAs) achieving superior characteristics compared with commercially available OAs, while keeping simple structures and a reduced number of parts. A single‐ended amplifier topology based on a junction field‐effect transistor (JFET) is proposed as a means of achieving very low input noise levels, both in current and voltage. It is direct‐coupled and allows to place a high‐pass filter at its input to preserve input range, or at its output to optimize noise. The proposed topology results in a low input capacitance and low input‐current noise, making it suitable for applications where multiple amplifiers are connected in parallel to achieve ultra‐low noise levels. The amplifier's gain is set by a resistor ratio, being suitable for instrumentation front ends. The circuit analysis and design equations are provided to adapt it for different applications and, as an example, an amplifier with a gain of 40 dB and a bandwidth from DC to 1 MHz was designed, built, and tested. The dominant noise contribution of the amplifier was the JFET (a JFE2140 device), featuring an input noise voltage of , that is reduced to when two amplifiers are connected in parallel.

Performance of a front-end prototype ASIC for the ATLAS High Granularity timing detector

This paper presents the design and characterisation of a front-end prototype ASIC for the ATLAS High Granularity Timing Detector, which is planned for the High-Luminosity phase of the LHC. This prototype, called ALTIROC1, consists of a 5 × 5-pad matrix and contains the analog part of the single-channel readout (preamplifier, discriminator, two TDCs and SRAM). Two preamplifier architectures (transimpedance and voltage) were implemented and tested. The ASIC was characterised both alone and as a module when connected to a 5 × 5-pad array of LGAD sensors. In calibration measurements, the ASIC operating alone was found to satisfy the technical requirements for the project, with similar performances for both preamplifier types. In particular, the jitter was found to be 15 ± 1 ps (35 ± 1 ps) for an injected charge of 10 fC (4 fC). A degradation in performance was observed when the ASIC was connected to the LGAD array. This is attributed to digital couplings at the entrance of the preamplifiers. When the ASIC is connected to the LGAD array, the lowest detectable charge increased from 1.5 fC to 3.4 fC. As a consequence, the jitter increased for an injected charge of 4 fC. Despite this increase, ALTIROC1 still satisfies the maximum jitter specification (below 65 ps) for the HGTD project. This coupling issue also affects the time over threshold measurements and the time-walk correction can only be performed with transimpedance preamplifiers. Beam test measurements with a pion beam at CERN were also undertaken to evaluate the performance of the module. The best time resolution obtained using only ALTIROC TDC data was 46.3 ± 0.7 ps for a restricted time of arrival range where the coupling issue is minimized. The residual time-walk contribution is equal to 23 ps and is the dominant electronic noise contribution to the time resolution at 15 fC.

A 121.4-dB DR Capacitively Coupled Chopper Class-D Audio Amplifier

This article presents a class-D amplifier (CDA) with high dynamic range (DR). To eliminate the typically dominant noise contribution of a resistive feedback network, the input and feedback signals are chopped and applied to a capacitive feedback network. However, this leads to high-voltage (HV) transients at the input of the loop filter, which, due to timing and impedance mismatch in the chopped feedback network, could degrade linearity and even overstress low-voltage (LV) core devices. Robust processing of the HV chopped feedback signal is guaranteed with chopper timing skew correction, chopper impedance matching, and deadbanding. The prototype, implemented in a 180-nm bipolar-CMOS-DMOS (BCD) process, achieves 121.4 dB of DR, 5.9 dB higher than state-of-the-art closed-loop CDAs, and 8- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}_{\mathrm {RMS}}$ </tex-math></inline-formula> output-referred noise (A-weighted). It also achieves a peak total harmonic distortion (THD) + N of −109.8 dB and a peak efficiency of 93%/88% while driving 15 W/26 W into an 8-/4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> load.

Evaluation of probabilistic constellation shaping performance in Flex Grid over multicore fiber dynamic optical backbone networks [Invited

In this paper, we present a worst-case methodology for estimating the attainable spectral efficiency over end-to-end paths across a Flex Grid over multicore fiber (MCF) optical network. This methodology accounts for physical link noise, as well as for the signal-to-noise ratio in the Add module ( S N R T X ) of spatial-division-multiplexing-enabled reconfigurable optical add and drop multiplexers (SDM-ROADMs), introducing a dominant noise contribution over that of their Bypass and Drop modules. The proposed methodology is subsequently used to quantify the benefits that probabilistic constellation shaping (PCS) can bring to Flex-Grid/MCF dynamic optical backbone networks, compared to using traditional polarization-multiplexed modulation formats. In a first step, insight is provided into the spectral efficiency attainable along the precomputed end-to-end paths in two reference backbone networks, either using PCS or traditional modulation formats. Moreover, in each one of these networks, two S N R T X values are identified: the S N R T X yielding the maximum average paths’ spectral efficiency, as well as an S N R T X that, although slightly degrading the average paths’ spectral efficiency (by 10%), would yet enable a cost-effective SDM-ROADM Add module implementation. Extensive simulations are conducted to analyze PCS offered load gains under 1% bandwidth blocking probability. Furthermore, the study lastly focuses on finding out whether lower fragmentation levels in Flex-Grid/MCF dynamic optical backbone networks can push PCS benefits even further.

Sensitivity, Noise and Resolution in a BEOL-Modified Foundry-Made ISFET with Miniaturized Reference Electrode for Wearable Point-of-Care Applications.

Ion-sensitive field-effect transistors (ISFETs) form a high sensitivity and scalable class of sensors, compatible with advanced complementary metal-oxide semiconductor (CMOS) processes. Despite many previous demonstrations about their merits as low-power integrated sensors, very little is known about their noise characterization when being operated in a liquid gate configuration. The noise characteristics in various regimes of their operation are important to select the most suitable conditions for signal-to-noise ratio (SNR) and power consumption. This work reports systematic DC, transient, and noise characterizations and models of a back-end of line (BEOL)-modified foundry-made ISFET used as pH sensor. The aim is to determine the sensor sensitivity and resolution to pH changes and to calibrate numerical and lumped element models, capable of supporting the interpretation of the experimental findings. The experimental sensitivity is approximately 40 mV/pH with a normalized resolution of 5 mpH per µm2, in agreement with the literature state of the art. Differences in the drain current noise spectra between the ISFET and MOSFET configurations of the same device at low currents (weak inversion) suggest that the chemical noise produced by the random binding/unbinding of the H+ ions on the sensor surface is likely the dominant noise contribution in this regime. In contrast, at high currents (strong inversion), the two configurations provide similar drain noise levels suggesting that the noise originates in the underlying FET rather than in the sensing region.

All-programmable low noise readout ASIC for silicon strip sensors in tracking detectors

The Programmable Read-out with Improved Noise-performance Charge Sensitive Amplifier (PRINCSA) is a prototype Application Specific Integrated Circuit (ASIC) designed for read-out of the silicon micro-strip sensors in the tracking detectors for Physics experiments. The main aim of this project was to minimize the overall system noise (Equivalent Noise Charge, ENC) and implement a range of programmable features to adjust the noise performance to varying conditions. The chip comprises three single-ended and three pseudo-differential channels that additionally allow for power supply interference reduction. All channels include a charge sensitive amplifier (CSA), a fast shaping amplifier for time measurements, and a slow shaping amplifier for amplitude measurements. The slow shaper’s architecture (in all channels) and its peaking time (in the single-ended channels) are configurable to test the capability of noise filtering for various dominant noise contributions (unipolar semi-Gaussian and complex conjugate poles filters). To further improve the power supply rejection ratio, additional on-chip filtering of the preamplifier biasing potential is included in every channel. For faster CSA baseline restoration, its feedback in all channels is equipped with a pulsed reset circuit. In this design, it is combined with a double-polarity Krummenacher circuit for leakage current compensation for both polarities of charge pulse and leakage current without compromising the large value of the CSA feedback resistance. The ASIC comprises a calibration circuit working in two operational modes: a standard double-polarity charge injection and a single-polarity charge injection (fast leading and slow falling edges of the calibration pulses) with programmable amplitude. The IC was fabricated in Q4 2018 using UMC CMOS 180 nm technology node.

Grating Spectrometry and Spatial Heterodyne Fourier Transform Spectrometry: Comparative Noise Analysis for Raman Measurements

The desire for portable Raman spectrometers is continuously driving the development of novel spectrometer architectures where miniaturisation can be achieved without the penalty of a poorer detection performance. Spatial heterodyne spectrometers are emerging as potential candidates for challenging the dominance of traditional grating spectrometers, thanks to their larger etendue and greater potential for miniaturisation. This paper provides a generic analytical model for estimating and comparing the detection performance of Raman spectrometers based on grating spectrometer and spatial heterodyne spectrometer designs by deriving the analytical expressions for the performance estimator (signal-to-noise ratio, SNR) for both types of spectrometers. The analysis shows that, depending on the spectral characteristics of the Raman light and on the values of some instrument-specific parameters, the ratio of the SNR estimates for the two spectrometers () can vary as much as by two orders of magnitude. Limit cases of these equations are presented for a subset of spectral regimes which are of practical importance in real-life applications of Raman spectroscopy. In particular, under the experimental conditions where the background signal is comparable or larger than the target Raman line and shot noise is the dominant noise contribution, the value of is, to a first order of approximation, dependent solely on the relative values of each spectrometer’s etendue and on the number of row pixels in the detector array. For typical values of the key instrument-specific parameters (e.g., etendue, number of pixels, spectral bandwidth), the analysis shows that spatial heterodyne spectrometer-based Raman spectrometers have the potential to compete with compact grating spectrometer designs for delivering in a much smaller footprint (10–30 times) levels of detection performance that are approximately only five to ten times poorer.

A 0.3–6 ​GHz noise and distortion cancelling LNA achieving an NF of 2.8±0.3 ​dB in 0.18-μm SiGe BiCMOS process

This paper presents a noise and distortion cancelling wideband low-noise amplifier (LNA) in JAZZ 0.18-μm SiGe BiCMOS process. In the proposed design, a shunt feedback (SFB) and a common-emitter (CE) paths are adopted to reduce the dominant noise contribution of the main path. To enhance the linearity, the derivative superposition method is modified to eliminate the whole nonlinearity components. Moreover, with the help of an n-type MOS acted as a resistive load of the CE path, both flat gain and acceptable output impedance matching are achieved. The measurement results exhibit that the LNA has an input third-order intercept point (IIP3) of −4 dBm with a noise figure (NF) of 2.8 ​± ​0.3 ​dB and a power gain 16.5 ​± ​0.2 ​dB from 0.3 to 6 ​GHz. The circuit draws 14.5 ​mA dc current from a 3.3 ​V supply for core area of 0.22 ​mm2.

Characterization and Optimization of Four-Wave-Mixing Wavelength Conversion System

In this work, we present a comprehensive experimental and numerical investigation of the impact of system parameters on wavelength converters based on four-wave-mixing, with focus on practical system implementations in addition to the interaction within the nonlinear medium. The input signal power optimization is emphasized according to the trade-off between the linear and the nonlinear impairments, and the origin of the limitations at the optimum is studied. The impact of the input signal quality on the converted idler is discussed, and depending on the dominant noise contribution a varying conversion penalty is demonstrated. The penalty is also shown to scale with increasing number of WDM channels due to additional nonlinear cross-talk between them. Finally, by means of numerical simulations we extend the experimental characterization to high pump powers, showing the impact of parametric noise amplification, and different pump laser linewidths, which lead to increased phase-noise transfer. The experimental characterization employs an integrated AlGaAs-on-insulator waveguide, and the numerical simulations accompany the results to make the analysis general for χ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</sup> materials that satisfy the assumptions of the split-step Fourier method.

A $${\mathbf{g}}_{{\mathbf{m}}}$$-boosted highly linear fully differential 3–5 GHz UWB LNA employing noise and distortion canceling technique

A novel structure is presented to optimize the noise and linearity performance of a $${\text{g}}_{\text{m}}$$ -boosted common gate (CG) ultra-wide-band low noise amplifier (LNA) by exploiting noise and distortion canceling technique. The $${\text{g}}_{\text{m}}$$ -booster common source amplifier provides a degree of freedom to eliminate the limitation on the noise figure (NF) improvement, at a lower transconductance for the CG transistor. The applied noise and distortion canceling technique to the $${\text{g}}_{\text{m}}$$ -boosted topology is used to minimize the dominant noise contribution and the second and third order non-linearity coefficients of the first stage components. The proposed LNA is configured in a differential topology to compensate the $$IIP_{2}$$ of the structure. The Forward body bias technique is utilized for operating the LNA at a lower supply voltage and power consumption. The post-layout simulation results of the LNA, including bonding and electrostatic discharge circuits, with 90 nm TSMC RF CMOS technology show a power gain of 14.5 ± 05 dB, flat NF of 2.2 ± 0.1 dB, and $$S_{11}$$ less than − 9.5 dB for 3–5 GHz frequency at a power consumption of 13.8 mW from 0.7 V supply voltage. The $$IIP_{3}$$ and $$IIP_{2}$$ measures are obtained as + 5.2 dBm and 55 dBm, respectively.

Low noise current preamplifier for qPlus sensor deflection signal detection in atomic force microscopy at room and low temperatures.

The resolution of frequency modulation atomic force microscopy is limited by instrumental noise. When using a qPlus sensor, the deflection detector noise is the dominant noise contribution. It can be reduced by improving the preamplifier used to amplify the sensor deflection signal. We present a simple single-stage differential preamplifier which outperforms previous designs known to us by at least a factor of two in the deflection noise density. We show specific versions of this preamplifier to use in ambient conditions, in ultra-high vacuum at room temperature, and at 4.2 K. Furthermore, we compare the thermal peak analysis and the frequency shift noise density method as a means to determine the deflection noise density. We note that this preamplifier can also be used for any current-generating sensors such as other piezoelectric sensors and photodiodes, but, in this paper, we restrict our analysis to qPlus sensors.

Confirmation of resting-state BOLD fluctuations in the human brainstem and spinal cord after identification and removal of physiological noise.

Resting-state functional MRI (rs-fMRI) has been used to investigate networks within the cortex, but its use in the brainstem (BS) and spinal cord (SC) has been limited. This region presents challenges for fMRI, partly because of sources of physiological noise. This study aims to quantify noise contributions to rs-fMRI, and to obtain evidence of resting-state blood oxygenation level-dependent (BOLD) fluctuations. Resting-state-fMRI data were obtained from the BS/SC in 16 participants, at 3 Tesla, with T2 -weighted single-shot fast spin-echo imaging. The peripheral pulse, respiration, and expired CO2 were recorded continuously. Physiological noise was modeled from these recordings, movement parameters, and white matter regions. Model fits were then subtracted from the data. BOLD contributions were then investigated through connectivity. Bulk motion was the largest contributor to the signal variance (19% of the total), followed by cardiac-related motion (14%), nonspecific signal variations detected in white matter (10%), respiratory-related motion (2.6%), and end-tidal CO2 variations (0.7%). After noise was removed, significant left-right connectivity was detected in the SC dorsal horns and ventral horns. Resting-state BOLD fluctuations are demonstrated in the SC, as are the dominant noise contributions. These findings are an essential step toward establishing rs-fMRI in the BS/SC. Magn Reson Med 78:2149-2156, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Dynamic range improvement of broadband microwave photonic links using a linearized single-sideband modulator

A novel linearized single-sideband modulator is proposed and demonstrated to generate optical single-sideband (OSSB) signal and improve the dynamic range of microwave photonic links. The modulator is composed of a dual-electrode Mach–Zehnder modulator (DEMZM) lying on the top branch and a phase shifter (PS) lying on the bottom branch. By optimizing the optical power split ratio of the linearized modulator and the phase shift of the PS, the third-order inter-modulation distortion (IMD3) can be efficiently suppressed while the second-order distortion components are eliminated simultaneously. It is a multi-octave linearization technique which can be applied for broadband systems. Simulation results show that, the linearized modulator can provide a spurious-free dynamic range (SFDR) of 130dB for a bandwidth of 1Hz at the received optical power of 2dBm assuming shot noise is the dominant noise contribution, which is 22dB higher than the conventional DEMZM. The effects of the finite extinction ratio of modulator, the phase deviation of PS and the dispersion of fiber on the linearization performance are also investigated.

A Linearized Optical Single-Sideband Modulation Analog Microwave Photonic Link Using Dual Parallel Interferometers

Dual parallel Mach-Zehnder interferometers (MZIs) are presented to linearize the optical single-sideband (OSSB) modulation analog microwave photonic link. By using a dual-drive Mach-Zehnder modulator at the transmit side of the link, an OSSB modulation can be obtained. By exploiting different RF responses of two MZIs at the receive end, the third-order intermodulation distortion (IMD3) is well suppressed and the spurious-free dynamic range (SFDR) is enhanced. More importantly, we demonstrate fundamental-to-IMD3 ratio of 49 dB for an RF input signal power value of 10 dBm, which is 24 dB more than a conventional OSSB modulation link, and SFDR of 132 dB for a bandwidth of 1 Hz at the received optical power of 8 dBm assuming shot noise is the dominant noise contribution, which is improved approximately 20 dB.

Time-Division-Multiplexed Interferometric Sensor Arrays

We propose and experimentally demonstrate a time-division-multiplexed acoustic sensor array employing multiple low-gain Er-doped fiber amplifiers to multiplex ten compact Fabry-Perot acoustic sensors. We show that the ten sensors can be interrogated with a single laser diode at a single wavelength, and exhibit the same measured SNR within $\pm$ 0.95 dB of each other. We present a model to identify the dominant noise contributions, and their dependence on the number of multiplexed sensors. This model predicts that more than 350 sensors can be multiplexed with the proposed architecture.

Subtraction of Newtonian noise using optimized sensor arrays

Fluctuations in the local Newtonian gravitational field present a limit to high precision measurements, including searches for gravitational waves using laser interferometers. In this work, we present a model of this perturbing gravitational field and evaluate schemes to mitigate the effect by estimating and subtracting it from the interferometer data stream. Information about the Newtonian noise is obtained from simulated seismic data. The method is tested on causal as well as acausal implementations of noise subtraction. In both cases it is demonstrated that broadband mitigation factors close to 10 can be achieved removing Newtonian noise as a dominant noise contribution. The resulting improvement in the detector sensitivity will substantially enhance the detection rate of gravitational radiation from cosmological sources.

Noise Performance of a Regulated Cascode Transimpedance Amplifier for Radiation Detectors

A low noise transimpedance amplifier (TIA) is used in radiation detectors to transform the current pulse produced by a photo-sensitive device into an output voltage pulse with a specified amplitude and shape. We consider here the specifications of a PET (positron emission tomography) system. We review the traditional approach, feedback TIA, using an operational amplifier with feedback, and we investigate two alternative circuits: the common-gate TIA, and the regulated cascode TIA. We derive the transimpedance function (the poles of which determine the pulse shaping); we identify the transistor in each circuit that has the dominant noise source, and we obtain closed-form equations for the rms output noise voltage. We find that the common-gate TIA has high noise, but the regulated cascode TIA has the same dominant noise contribution as the feedback TIA, if the same maximum transconductance value is considered. A circuit prototype of a regulated cascode TIA is designed in a 0.35 μm CMOS technology, to validate the theoretical results by simulation and by measurement.

Broadband phase noise suppression in a Yb-fiber frequency comb

We report a simple technique to suppress high-frequency phase noise of a Yb-based fiber optical frequency comb using an active intensity noise servo. Out-of-loop measurements of the phase noise using an optical heterodyne beat with a cw laser show suppression of phase noise by ≥7 dB out to Fourier frequencies of 100 kHz with a unity-gain crossing of ∼700 kHz. These results are enabled by the strong correlation between the intensity and phase noise of the laser. Detailed measurements of intensity and phase noise spectra, as well as transfer functions, reveal that the dominant phase and intensity noise contribution above ∼100 kHz is due to amplified spontaneous emission or other quantum noise sources.

Improved quality of optical coherence tomography imaging of basal cell carcinomas using speckle reduction

Optical coherence tomography (OCT) is a possible imaging method for delineation of non-melanoma skin cancer. Speckle noise is the dominant noise contribution in OCT images; it limits the ability to identify cellular structures especially skin cancer. QUESTIONS ADDRESSED: This report suggests a method for improving OCT image quality for skin cancer imaging. OCT is an optical imaging method analogous to ultrasound. Two basal cell carcinomas (BCC) were imaged using an OCT speckle reduction technique (SR-OCT) based on repeated scanning by altering the distance between the probe and the surface of the skin. SR-OCT resulted in improved visualisation and more accurate thickness measurements in BCC lesions. This OCT speckle reduction method led to improved visualisation and better defined delineations in two BCC lesions. Thus, OCT was improved to a clinically relevant level when imaging BCC lesions.

Effect of Interfacial Oxide Thickness on 1/f Noise in Polysilicon Emitter BJTs

The role of the interfacial oxide (IFO) between the polysilicon and monosilicon emitter regions on the noise behavior of n-p-n poly-emitter bipolar transistors was investigated through 1/f noise measurements. Bipolar junction transistors with different IFO thickness, and emitter geometry were utilized. Measurements with variable external base bias resistance (R/sub S/) were used to investigate the relative contribution of each individual noise source from the base current (S/sub IB/), the collector current (S/sub IC/) and, the internal emitter and base series resistances (S/sub Vr/). When the voltage noise power spectral densities S/sub VC/ and S/sub VB/ were measured across resistances in series with the collector and base, respectively, using a relatively large R/sub S/ (/spl sim/1 M/spl Omega/), S/sub IB/ was found to have the dominant noise contribution at lower bias currents. On the other hand, when the voltage noise power spectral densities S/sub VC/ and S/sub VE/ were measured across resistances in series with the collector and emitter, respectively, in a different experimental setup with a low R/sub S/ value, S/sub Vr/ was found to have the dominant noise contribution at higher bias currents. IFO was found to increase S/sub IB/, S/sub IC/, and S/sub Vr/. S/sub IB/ was modeled as a combination of tunneling and diffusion fluctuations of the minority carriers in the emitter; whereas S/sub IC/ was modeled as a combination of number and diffusion fluctuations of the minority carriers in the base. S/sub Vr/ was attributed to the internal emitter resistance noise originating from the fluctuation in the majority carrier flow through the IFO.