Low-noise Junction Field-effect Transistor Research Articles

Low-Noise Programmable Voltage Source

This paper presents the design and testing of a low-noise programmable voltage source. Such a piece of instrumentation is often required as part of the measurement setup needed to test electronic devices without introducing noise from the power supply (such as photodetectors, resistors or transistors). Although its construction is based on known configurations, here the discussion is focused on the characterization and the minimization of the output noise, especially at very low frequencies. The design relies on a digital-to-analog converter, proper lowpass filters, and a low-noise Junction Field-Effect Transistors (JFET) based voltage follower. Because of the very low level of output noise, in some cases we had to resort to cross-correlation in order to reduce the background noise of the amplifiers used for the characterization of the programmable source. Indeed, when two paralleled IF9030 JFETs are used in the voltage follower, the output noise can be as low as 3 nV/√Hz, 0.6 nV/√Hz and 0.4 nV/√Hz at 1 Hz, 10 Hz and 100 Hz, respectively. The output voltage drift was also characterized and a stability of ±25 µV over 3 h was obtained. In order to better appreciate the performance of the low-noise voltage source that we have designed, its noise performances were compared with those of a set-up based on one of the best low-noise solid-state voltage regulators available on the market. Actual measurements of the current noise in a type-II superlattice photodetector are reported in which the programmable source was used to provide the voltage bias to the device.

Ultra-Low-Noise Balanced Detectors for Optical Time-Domain Measurements

Two ultra-low-noise balanced detectors used for optical time-domain measurements are presented in this paper. Both simultaneously achieve high bandwidth and low noise that is extremely difficult to realize in commercial detectors. Two-stage amplification circuits based on transimpedance amplifiers (TIAs) were used for these detectors, with special modifications implemented for different applications. To further suppress noise, a low-noise junction field-effect transistor is connected between the photodiode and TIA to reduce the impact of amplifier leakage current in one of the detectors. Benefiting from this design, a 70-MHz sensitive detector with a gain of 3.2E5 V/W and low noise-equivalent power (NEP) density of 2.2 pW/rtHz was implemented. For another balanced detector used in higher bandwidth applications, the differential TIA circuit is used, with the detector achieving a 250-MHz bandwidth with a gain of 5E4 V/W, equivalent to NEP of 6.2 pW/rtHz. Due to the difficulty of achieving high bandwidth with low noise, we perform theoretical analysis and simulations for our designs to ensure that these two design goals are realized simultaneously. The performance of the detectors is consistent with our analysis. In addition, a simplified optical testing system was built to test and calculate the performance of the detectors in their respective applications. The results show that both detectors are well-balanced and achieve a common mode rejection ratio greater than 50 dB.

CMOS-Integrated Low-Noise Junction Field-Effect Transistors for Bioelectronic Applications.

In this work, we present a CMOS-integrated low-noise junction field-effect transistor (JFET) developed in a standard 0.18 pm CMOS process. These JFETs reduce input-referred flicker noise power by more than a factor of 10 when compared to equally sized n-channel MOS devices by eliminating oxide interfaces in contact with the channel. We show that this improvement in device performance translates into a factor-of-10 reduction in the input-referred noise of integrated CMOS operational amplifiers when JFET devices are used at the input, significant for many applications in bioelectronics.

Programmable, very low noise current source.

We propose a new approach for the realization of very low noise programmable current sources mainly intended for application in the field of low frequency noise measurements. The design is based on a low noise Junction Field Effect Transistor (JFET) acting as a high impedance current source and programmability is obtained by resorting to a low noise, programmable floating voltage source that allows to set the sourced current at the desired value. The floating voltage source is obtained by exploiting the properties of a standard photovoltaic MOSFET driver. Proper filtering and a control network employing super-capacitors allow to reduce the low frequency output noise to that due to the low noise JFET down to frequencies as low as 100 mHz while allowing, at the same time, to set the desired current by means of a standard DA converter with an accuracy better than 1%. A prototype of the system capable of supplying currents from a few hundreds of μA up to a few mA demonstrates the effectiveness of the approach we propose. When delivering a DC current of about 2 mA, the power spectral density of the current fluctuations at the output is found to be less than 25 pA/√Hz at 100 mHz and less than 6 pA/√Hz for f> 1 Hz, resulting in an RMS noise in the bandwidth from 0.1 to 10 Hz of less than 14 pA.

A low noise single-transistor transimpedance preamplifier for Fourier-transform mass spectrometry using a T feedback network

A novel single-transistor transimpedance preamplifier has been introduced for improving performance in Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. A low noise junction field-effect transistor (JFET), BF862, is used as the main amplification stage of this trans-impedance preamplifier, and a T-shaped feedback network is introduced as both the feedback and the gate biasing solutions. The T feedback network has been studied using an operational amplifier (Op Amp), AD8099. Such a feedback system allows ~100-fold less feedback resistance at a given transimpedance, hence preserving bandwidth, which is beneficial to applications demanding high gain. The single-transistor preamplifier yields a tested transimpedance of ~10(4) Ω (80 dBΩ) in the frequency range between 1 kHz and 1 MHz (mass-to-charge ratio, m/z, of around 180-180k for a 12-T FT-ICR system), with a low power consumption of ~6 mW, which implies that this preamplifier is well suited to a 12-T FT-ICR mass spectrometer. In trading noise performance for higher trans-impedance, an alternative preamplifier design, an AD8099 preamplifier with the T feedback network, has also been studied with a capability of ~10(6) Ω (120 dBΩ) transimpedance in the same frequency range. The resistive components in the T feedback network reported here can be replaced by complex impedances, which allows adaptation of this feedback system to other frequency, transimpedance, and noise characteristics for applications not only in other mass spectrometers, such as Orbitrap, time-of-flight (TOF), and ion trap systems, but also in other charge/current detecting systems such as spectroscopy systems, microscopy systems, optical communication systems, or charge-coupled devices (CCDs).

Measurement of Low-Frequency Noise of Modern Low-Noise Junction Field Effect Transistors

A description of the low-noise measurement system designed for experimental investigation of low-frequency noise of modern low-noise junction field effect transistors (JFETs) at a frequency range from 0.5 Hz to 50 kHz is presented. The noise floor of the system in terms of noise voltage spectral density is about 1.3 nV//spl radic/Hz at frequency 0.5 Hz, 0.6 nV//spl radic/Hz at frequency 1 Hz, 0.08 nV//spl radic/Hz at frequency 10 Hz, and /spl les/0.04 nV//spl radic/Hz at frequencies 100 Hz-50 kHz. Such a system makes it possible to measure 1/f noise and channel thermal noise of modern very low noise n-channel JFETs. Specifically, discrete samples of JFETs, IF9030, IF1801, IF3601, and 2N4338, were investigated at the frequency range mentioned above. The system provided negligible contribution of all noise sources except intrinsic noise of measured JFETs which was a 1/f noise at frequencies f < 10 Hz and a channel thermal noise at frequencies f /spl ges/ 10 Hz. The measured values of the equivalent input noise voltage spectral density e/sub n/ of the best samples from investigated JFETs IF9030, IF1801, IF3601, and 2N4338 were 2.7, 3.2, 3.4, and 22 nV//spl radic/Hz at frequency 0.5 Hz; 1.5, 2.1, 1.8, and 14 nV//spl radic/Hz at frequency 1 Hz; and 0.5, 0.4, 0.6, and 3.2 nV//spl radic/Hz at frequencies more than 1 kHz, correspondingly.

Frequency dependence of glass encapsulated electrometer resistors

The frequency dependence of the resistance of commercial 1-1000 G/spl Omega/ electrometer resistors has been measured from 30 Hz to 30 kHz. When scaled appropriately, the data for devices of similar geometry fall on a single curve, indicating that the frequency dependence is due to distributed capacitance, rather than to frequency dependence of the resistivity. The results are important for understanding noise performance when these devices are used as gate bias resistors in low-noise junction field effect transistor circuits.

High Energy Resolution X-Ray Spectrometer for High Count Rate Xrf Applications

AbstractA new x-ray spectrometer has been constructed which incorporates a novel large area, low capacitance Si(Li) detector and a low noise JFET (junction field effect transistor) preamplifier. The spectrometer operates at high count Tates without the conventional compromise in energy resolution. For example, at an amplifier peaking time of 1 p.sec and a throughput count rate of 145,000 counts sec-1, the energy resolution at 5.9 keV is 220 eV FWHM. Commercially available spectrometers utilizing conventional geometry Si(Li) detectors with areas equivalent to the new detector have resolutions on the order of 540 eV under the same conditions. Conventional x-ray spectrometers offering high energy resolution must employ detectors with areas one-tenth the size of the new LBL detector (20 mm2 compared with 200 mm2). However, even with the use of the smaller area detectors, the energy resolution of a commercial system is typically limited to approximately 300 eV (again, at 1 μsec and 5.9 keV) due to the noise of the commercially available JFET's. The new large area detector is useful in high count rate applications, but is also useful in the detection of weak photon signals, in which it is desirable to subtend as large an angle of the available photon flux as possible, while still maintaining excellent energy resolution. X-ray fluorescence data from die new spectrometer is shown in comparison to a commercially available system in the analysis of a dilute muhi-element material, and also in conjunction with high count rate synchrotron EXAFS applications.

Low Noise Junction Field Effect Transistors Exposed to Intense Ionizing Radiation

The low noise junction field effect transistor (JFET) is an essential active component in the input stages of low noise amplifiers. The changes in the characteristics of low noise JFETs have been studied after exposure to high doses of intense ionizing radiation as may be experienced in nuclear and space applications. The experimental results show that the source-drain current, transconductance and threshold voltage are only slightly degraded and that the gate junction leakage current and the noise voltage generated by the JFET both increase considerably, the latter especially at low frequencies. It is concluded from the results that JFETs should perform in low noise amplifiers provided the radiation dose does not exceed 10 Krad (Si), and that JFETs should be useable as active devices to very high doses if allowance is made for the degraded gate junction properties in specially designed circuits.

Methods of Reducing Noise of Junction Field Effect Transistor (JFET) Amplifiers

At present in non-dispersive X-ray spectrometers the electronic noise of the pulse amplifier input circuit prevents full realization of the inherent resolution of the semiconductor detector. Commercially available low noise JFET's encapsulated with boro-silicate (7052)glass insulated headers have typical noise contributions to detector resolution widths (FWHM), at 25°C, of 326 eV (Si). JFET's encapsulated with BeO or Al2O3 headers contribute ~200 eV to the resolution at 25°C and 150 eV at about -20°C. Techniques to select passive components which do not inhibit the performance of these transistors are discussed.