Equivalent Input Current Noise Research Articles

A low noise CLASS AB operational amplifier with high voltage output capability by 180 nm BCD process

Abstract In this work, a low noise CLASS AB operational amplifier, which can output high voltage, has been fabricated by a 180 nm BCD process. For the objective of achieving low noise, the bipolar junction transistor (BJT) input stage with the base current compensation structure is employed. Experimental results show that the low noise amplifier’s equivalent input current and voltage noise are 3.2 pA/sqrt (Hz) and 16.73 nV/sqrt (Hz) separately, and the rising and falling slew rates are 10.40 MV/s and 6.67 MV/s separately. With the die area of 0.629 mm2, the amplifier’s power consumption is 18.3 mW, which flows 60 μA on the 5 V low power supply and 600 μA on the 25 V high power supply.

Low-noise chopper amplifier design for low-frequency induction magnetometers

Abstract Induction magnetometers (IM) are commonly used in the magnetotelluric method for exploration. 1/f noise in the low-frequency band of the preamplifier reduces the signal-to-noise ratio of IM, thus affecting the exploration results. We designed a low-noise chopper amplifier with equivalent input voltage noise of 9.8 nV/√Hz at 1 mHz, 2.1 nV/√Hz at 0.01 Hz, and 1.9 nV/√Hz at 0.1 Hz; 1/f noise corner frequency of 8 mHz, and equivalent input current noise of 200 fA/√Hz at 1 mHz, 100 fA/√Hz at 0.01 Hz, and 60 fA/√Hz at 0.1 Hz. The IM using this chopper amplifier is 85.5 cm long, 6.0 cm in diameter, and has a total weight of 4.8 kg. Its sensitivity is 300 mV/nT during 20 Hz and 1 kHz, with a theoretical equivalent input magnetic field noise of 0.3 pT/√Hz at 1 Hz and a measurement frequency range of 1 mHz to 1 kHz.

Ultralow Noise Low Offset Chopper Amplifier for Induction Coil Sensor to Detect Geomagnetic Field of 1 mHz to 1 kHz

An induction coil sensor (ICS) is important for measuring low-frequency (DC-1kHz) geomagnetic field. The accuracy of the preamplifier is one key factor determining the performance of the sensor. But the preamplifier is susceptible to 1/ f noise, offset voltage and drift. In order to eliminate these influences, a preamplifier circuit with three amplifier stages based on chopper technology has been designed, and its performance has been tested. The results show that: 1) The 1/ f noise corner frequency is 3 mHz, the equivalent input voltage noise (EIVN) level of the circuit is [Formula: see text] and [Formula: see text]; 2) The equivalent input current noise (EICN) level of the circuit is [Formula: see text]; 3) The offset voltage is about 600 nV, and the time drift performance is excellent. In conclusion, the preamplifier circuit has characteristics of ultralow noise, low offset voltage and low time drift. It can effectively amplify low-frequency weak geomagnetic signals from 1 mHz to 1 kHz and provides excellent performance for low-frequency ICS.

A Highly Sensitive In Situ CDOM Sensor Based on Frequency Spectrum Shifted m-Sequence Modulation

An in situ colored dissolved organic matter sensor based on a frequency spectrum shifted maximum-length sequence (FSSM) modulation method was proposed in this paper. The energy behavior resulting from the direct maximum-length sequence (m-sequence) modulation method was analyzed. We found a kind of twice modulation method, which optimizes m-sequence frequency spectrum structures. This novel method can effectively reduce the energy loss caused by filtering and reduce the noise introduced by demodulation. The sensitivity of the developed sensor was improved to an unprecedented level by optimizing the modulation/demodulation scheme without increasing the light-emitting diode intensity. Subsequently, we developed a cost-saving hardware sensor which can meet the requirements of the in situ measuring system with the FSSM modulation method. The equivalent input noise current of the electronic system can be as low as 12.20 fA. The limit of detection (LOD) of the sensor reached a maximum of 0.0168 μg/L within a concentration range of 0-3000 μg/L, and with an R-squared value of 0.9967. The results demonstrated that the LOD of our sensors was fivefold higher than the LOD of commercially available chromophoric dissolved organic matter (CDOM) sensors and doubled its normal detection range. The sensor also exhibited excellent anti-interference ability and it can attenuate sunlight and electromagnetic interference by up to ten times while improving the stability of the system. The improvement of the CDOM sensor's performance is of great significance to the marine environmental information monitoring field.

Common mode electronic noise in differential circuits

Differential circuits are assumed to reject common-mode noise yet no parameter is available to describe that rejection as the Common Mode Rejection Ratio (CMRR) applies only to deterministic signals, not to random noise. We propose a model and a method to analyze the contribution of the input common-mode electronic noise to the output voltage noise of differential circuits. The analysis shows that the same parameter-matching conditions that improve the CMRR determine common-mode noise rejection but CMRR is more sensitive to mismatching. For example, a low-frequency CMRR as low as 8 dB implies that more than 82% of common-mode noise is rejected. Thus, often only differential-mode noise is relevant. However, if the equivalent input current noise sources predominate over equivalent input voltage noise sources, cross-correlation between them partially yields common-mode noise that will also be rejected. We also propose a simple test that yields an estimate of that correlation.

Optimal Design of Low-Noise Induction Magnetometer in 1 mHz–10 kHz Utilizing Paralleled Dual-JFET Differential Pre-Amplifier

The optimal design of the induction magnetometer in the frequency band from 1 mHz to 10 kHz was analytically and experimentally investigated to achieve a suitable sensor configuration under a given noise equivalent magnetic induction (NEMI) and volume limitation. The transducer model is first analyzed, and the parameters $ {R}$ , $ {L}$ , $ {C}$ , and $\mu _{\rm {app}}$ are calculated. The equivalent input voltage noise that utilizes an n-paralleled dual- Junction Field-Effect Transistor (JFET) differential pre-amplifier, was decreased by $\surd \text{n}$ times, and the equivalent input current noise was increased by $\surd \text{n}$ times. The noise calculation formulas are derived based on the mathematical principle of the flux-feedback induction magnetometer, and the NEMI was immediately calculated. A set of sensor configurations, which reached the given NEMI, were achieved by solving the NEMI equation. The optimal sensor configuration was obtained, considering the smallest coil outer diameter limitation. To verify the theoretical analysis, the optimal induction magnetometer was manufactured, and its NEMI was measured in an electromagnetic shielding room. The experimental results show good agreement with the theoretical analysis. Furthermore, the optimal induction magnetometer had a smaller volume with a similar NEMI level compared with the well-known sensor MFS-06.

Characterization of SQUID-Based Null Detector for a Quantum Metrology Triangle Experiment

We present characterization of a null detector designed for an experiment aimed to close the quantum metrological triangle (QMT). The device is a SQUID amplifier equipped with a large winding-ratio planar input transformer improving the current resolution. We demonstrate equivalent input current noise down to 14 fA/Hz1/2. Furthermore, operation in a realistic environment of a dry dilution refrigerator hosting the QMT experiment is studied. We discuss particular challenges set by such system as the cryogenics introduces relatively large magnetic interference. We present data from measurements simulating the final QMT experiment and introduce the requirements for the averaging and bias reversal.

Multichannel Amplifier Topologies for High-Sensitivity and Reduced Measurement Time in Voltage Noise Measurements

In this paper, we discuss a few techniques that allow an effective reduction of the background noise and/or the reduction of the measurement time when performing voltage noise measurements by employing a number of nominally identical voltage amplifiers with negligible equivalent input current noise. It is demonstrated in particular that, if N (N > 2) voltage amplifiers are connected to the device under test and if the properties of cross-correlation among all <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> acquisition channels connected to the output of each amplifier are exploited, the time required for obtaining a given accuracy is reduced by a factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> - 1)/2 with respect to the conventional setup for cross-correlation that employs only two channels. From another point of view, the effective background noise is reduced for constant measurement time. Such a factor can be further increased if amplifier paralleling is also employed for reducing the equivalent input voltage noise for each channel. Measurements on two different setups employing up to four channels and up to eight channels are presented that confirm the expected reduction factors in measurement times.

Characterization of photoreceivers for LISA

LISA will use quadrant photoreceivers as front-end devices for the phasemeter measuring the motion of drag-free test masses in both angular orientation and separation. We have set up a laboratory testbed for the characterization of photoreceivers. Some of the limiting noise sources have been identified and their contribution has been either measured or derived from the measured data. We have built a photoreceiver with a 0.5 mm diameter quadrant photodiode with an equivalent input current noise of better than 1.8 pA Hz−1/2 below 20 MHz and a 3 dB bandwidth of 34 MHz.

An ultralow noise preamplifier for low frequency noise measurements

Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms.

Low-Noise Large-Area Quad Photoreceivers Based on Low-Capacitance Quad InGaAs Photodiodes

We report a large-area quad photoreceiver (2 times 2 array) having an equivalent input current noise density of <3.2 pA/radicHz per quadrant up to a 3-dB bandwidth of ~20 MHz. The low-noise photoreceiver performance is enabled by a 1-mm diameter quad p-i-n InGaAs photodiode having 2.5-pF capacitance per quadrant at 5-V reverse bias.

Full Model and Characterization of Noise in Operational Amplifier

In this paper, we propose a method to fully characterize noise in operational amplifiers (op-amps). The method allows the extraction not only of the spectra of the equivalent input current noise (EICN) and equivalent input voltage noise generators but also of their cross-correlation coefficients, which are routinely discarded in noise analysis of op-amps. The method is applied to extract all noise parameters of the low-noise bipolar-input op-amp OP27 and is validated through noise measurements in a test circuit. A key finding is that neglecting the cross-correlation coefficient between the two EICN generators can lead to severe errors in noise analysis.

A New Circuit Topology for the Realization of Very Low-Noise Wide-Bandwidth Transimpedance Amplifier

In this paper, after discussing some important limitations of the most common circuital configuration that is used for the realization of very low-noise transimpedance amplifiers, we propose and analyze a new circuit topology which allows us to obtain significant advantages as far as equivalent input current noise and bandwidth (BW) are concerned. We present a simple circuit implementation of the new transimpedance amplifier, together with the results of its noise characterization. The comparison between these measurements and those obtained on a conventional transimpedance amplifier with the same transimpedance gain has confirmed that the proposed approach allows us to obtain a lower background noise and a larger BW for the same transimpedance gain.

Transimpedance amplifier with 120 dB dynamic range

A transimpedance amplifier (TIA) with compression of the input current is presented. The proposed TIA has two regions of operation: a linear one for small input currents and one with compression for highcurrents, which would otherwise saturate the TIA. The measured −3 dB bandwidth is 102 MHz, the equivalent RMS input current noise is 20.2 nA and the maximal current overdrive is 20.5 mA, leading to a dynamic range at the input of 120 dB.

Enhanced Sensitivity Cross-Correlation Method for Voltage Noise Measurements

Ultralow noise measurements often require the application of signal processing and correction techniques to go beyond the noise performances of front-end amplifiers. In this paper, a new method for the voltage noise measurement is proposed, which allows, at least in principle, the complete elimination of the noise introduced by the amplifiers used for the measurements. This is obtained by resorting to the conventional cross-correlation technique for the elimination of the contribution of the equivalent input voltage noise of the amplifiers and by using a new three-step-measurement procedure that exploits different amplifier-configuration measurements in order to subtract the contribution of the equivalent input current noise of the amplifiers

Design of narrow-band photoreceivers by means of the photodiode intrinsic conductance

The photodiode intrinsic conductance is a versatile parameter for designing photoreceivers used in lightwave-microwave systems. A short review is given on how the transimpedance and equivalent input noise current of an optical receiver can be calculated. The design of monolithically integrated narrow-band photoreceivers for microwave-via-fiber applications at 10 GHz is demonstrated. The photoreceivers were fabricated using GaAs-based pseudomorphic high electron-mobility transistor monolithically integrated with metamorphic InGaAs photodiodes. For such a photoreceiver, a very low equivalent input noise current of 5.7 pA per square-root hertz and a high optoelectronic conversion gain of 64.1 dBV/W were measured in good agreement with simulations.

DC SQUID series array amplifiers with 120 MHz bandwidth (corrected)

We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 pm center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA//spl radic/Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.

DC SQUID series array amplifiers with 120 MHz bandwidth

We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 /spl mu/m center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/ Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.

Correlation between equivalent input noise generators

Correlation between equivalent input voltage and current noise sources is usually considered to be unimportant by low-frequency circuit designers. This paper shows that measurements of noise figure as a function of source resistance make it possible to determine the spectral densities of the equivalent input noise generators and the correlation between them. Measurements were made on five different types of operational amplifier and considerable correlation was found in three of these.

Unified analytical expressions for transimpedance and equivalent input noise current of optical receivers

Unified analytical expressions are derived for calculating the equivalent input noise current and transimpedance of optical receiver front ends with arbitrary input matching network topologies. To be independent of any transistor or amplifier type, noise parameters are used to describe the noise behavior of the active device. A new characteristic frequency-dependent value, called photodiode intrinsic conductance, is introduced. This figure-of-merit allows one to compare the achievable equivalent input noise current and transimpedance of different types of photodiodes independently of amplifier type and geometry.