Low-noise Preamplifier Research Articles

Superconducting radiation detector by using a microfabricated MgB2 meander line

The thermal response of an MgB2 detector was examined by using the irradiation of a 20ps pulse laser with the aid of ultra low-noise cryogenic preamplifier. High-quality MgB2 thin films were prepared by a sputtering technique. This device can be used as a novel neutron detector by employing the 10B(n,α)7Li nuclear reaction with a local energy release of 2.3MeV. This would be able to count individual neutrons with a repetition rate much faster than 106 per second.

ASIC With Multiple Energy Discrimination for High-Rate Photon Counting Applications

An ASIC for high rate photon counting measurements with multiple energy discrimination is presented. Optimized for pixelated CdZnTe sensors, the ASIC is composed of 64 channels with low-noise charge preamplification, high-order shaping (40ns minimum peaking time), and five window-discriminators with associated 16-bit counters. An efficient readout scheme allows simultaneous measurement and readout through a 60 MHz 16-bit output bus. The ASIC architecture and experimental results are reported, and the impact of the shaper order on the resolution, ballistic deficit, and pile-up is discussed.

A low-noise, low stored energy preamplifier for high-voltage radiation detectors

A low-noise preamplifier with very low stored energy has been developed for use with high-voltage radiation detectors. The input will withstand 3.5 kV, has a physical capacitance to ground of 200 pF, and an effective “small signal” capacitance of ∼30 nF. When connected to a high-voltage electrode, the low physical input capacitance to ground limits the stored energy and helps protect the detector system should an accidental discharge occur. The large effective input capacitance minimizes the voltage transient on the high-voltage electrode that occurs during charge collection, thus lowering the charge that is capacitively coupled to surrounding electrodes from this transient. If the surrounding electrodes are part of a position sensing readout, then this coupled charge is distributed uniformly among readout electrodes and is added to the signal charge induced by the motion of charge carriers containing position information. This introduces an error into the position centroid calculation. The preamplifier presented here greatly reduces this effect while keeping stored energy low. Equivalent input noise charge (ENC) is 256 electrons RMS when using a 250 ns unipolar shaping amplifier and no input capacitance. With input capacitances of 18 and 223 pF, the noise increases to 361 and 1766 electrons RMS, respectively.

Advances in particle identification in AMS at low energies

Special gas ionisation detectors have been developed for AMS at low energies (0.3–3MeV). By using very thin silicon nitride foils as entrance windows and low-noise preamplifiers, significant improvements in the performance has been obtained. In addition, electronic noise has been reduced by a compact design which minimises cable length and input capacitance. The resolution has been systematically studied as a function of energy for various projectiles ranging from protons to uranium. Energy straggling in the thin entrance foil is only a minor contribution to the total energy resolution. For heavier ions zp>6 the resolution is limited by the statistical nature of the ionisation process in the counter gas. For light elements, the electronic noise is the dominant contribution to the resolution. Particle identification with ΔE−E techniques has been studied as well. Good isobar separation for 10Be–10B can be obtained in the energy range of 0.3–0.8MeV. Also isobaric molecules such as BeH and CH can be identified in the energy range of 1MeV. These advances in detector performance represent an essential step forward in the development of multi-isotope AMS facilities at low energies. The detector development has also a potential for application in other fields of research where good energy resolution and particle identification is needed.

14N nuclear quadrupoleresonance of p-nitrotoluene using a high-Tc rf SQUID

Using a high-Tc radio-frequency superconducting quantum interference device (rf SQUID), wesuccessfully detected nuclear quadrupole resonance (NQR) at about 887 kHz for14N inp-nitrotoluene (PNT). A normal metal transformer made of copper wire was used to improve the sensitivity ofthe high-Tc rf SQUID and pulse-controlled rf switches and cross diodes were inserted in the transformer to reducethe influence of the strong excitation field. The preliminary results for NQR detection using thehigh-Tc SQUID had a similar signal-to-noise ratio to that of using a low noise preamplifier.

Front-end ASICs development for W–Si calorimeter at ILC (CALICE collaboration)

An ASIC (FLC_PHY3) has been developed to read out the test-beam prototype of the future international linear collider (ILC) tungsten–silicon calorimeter. It consists of 18 channels low-noise charge preamplifiers, bi-gain CRRC2 180 ns shapers, 12-bit track-and-hold, and a 5 MHz output multiplexer. It covers a dynamic range of 14 bits with a noise of 3500 e − with the 70 pF detector and a linearity at the per-mil level. The chip dissipates 6 mW/channel and 1000 chips have been produced in AMS 0.8 μm BiCMOS technology in 2003. One channel has recently been migrated into 0.35 μm, improving the series noise by 20% and the 1/ f noise by two. Besides, a power pulsing feature has been added in order to exploit the 1% duty cycle of the accelerator. This feature is a key parameter for ILC, as it is mandatory to embed the front-end inside the detector, without spoiling the Moliere radius with cooling pipes. Preliminary results indicate a good behavior in pulsing mode and several hundred channels have been produced of the recent version including this feature (FLC_PHY4), to be tested extensively in test beam at CERN in autumn 2006. FLC_PHY4 also includes a 12-bit ADC in order to take a step to the final version, which will send digital data out.

The electronics readout and the DAQ system of the DRAGO Anger Camera

The aim of the DRAGO project, supported by Italian INFN, is the development of a high-resolution, compact γ-ray imager, based on the Anger Camera principle. In this configuration, the light generated by a unique scintillator is read by an array of 77 Silicon Drift Detectors. In order to locate the position of interaction of the photon inside the scintillator, it is necessary to make an amplification and filtering of the detector signals followed by a processing of the acquired data. The electronics readout and processing system can be divided in two separate parts: the analog front end and the DAQ board. The analog front end is composed of 80 readout channels divided in 10 CMOS chips, produced in the 0.35 μm AMS technology, each one processing 8 channels. Each analog channel of the circuit includes a low-noise preamplifier, a sixth-order semigaussian shaping amplifier with four selectable peaking times from 1.8 μs up to 6 μs, a peak stretcher and a baseline holder. The energy resolution measured using a single channel of the chip with a Silicon Drift Detector Droplet (SD 3) is of 128 eV FWHM at 6 keV with the detector cooled at −20 °C. The 8 analog channels of the chip are multiplexed to a single analog output and fed to the acquisition system. For each γ event, this system performs the A/D conversion of all the signals of the array and sends them to a host PC, where the position reconstruction algorithm is executed. The DAQ board contains 10 ADCs, each one dedicated to a single ASIC of the analog section and having a resolution of 13 bit (ENOB). The burst conversion rate of the 10 ADCs together is 50 Ms/s resulting in a dead time of about 2 μs/event. The converted data are stored in a FIFO memory, for buffering, and then are transferred to the host PC via a USB 2.0 interface, which allows an event rate of more than 40k events/s for the whole Anger Camera, compatible with the application.

A front-end readout mixed chip for high-efficiency small animal PET imaging

Today, the main challenge of Positron Emission Tomography (PET) systems dedicated to small animal imaging is to obtain high detection efficiency and a highly accurate localization of radioisotopes. If we focus only on the PET characteristics such as the spatial resolution, its accuracy depends on the design of detector and on the electronics readout system as well. In this paper, we present a new design of such readout system with full custom submicrometer CMOS implementation. The front end chip consists of two main blocks from which the energy information and the time stamp with subnanosecond resolution can be obtained. In our A Multi-Modality Imaging System for Small Animal (AMISSA) PET system design, a matrix of LYSO crystals has to be read at each end by a 64 channels multianode photomultiplier tube. A specific readout electronic has been developed at the Hubert Curien Multidisciplinary Institute (IPHC, France). The architecture of this readout for the energy information detection is composed of a low-noise preamplifier, a CR-RC shaper and an analogue memory. In order to obtain the required dynamic range from 15 to 650 photoelectrons with good linearity, a current mode approach has been chosen for the preamplifier. To detect the signal with a temporal resolution of 1 ns, a comparator with a very low threshold (∼0.3 photoelectron) has been implemented. It gives the time reference of arrival signal coming from the detector. In order to obtain the time coincidence with a temporal resolution of 1 ns, a Time-to-Digital Converter (TDC) based on a Delay-Locked-Loop (DLL) has been designed. The chip is fabricated with AMS 0.35 μm process. The ASIC architecture and some simulation results will be presented in the paper.

Evaluation of silicon photomultipliers: A promising new detector for MR compatible PET

The Silicon Photomultiplier (SiPM) is a compact detector which shows great promise for use in MR compatible PET systems. SiPMs are insensitive to magnetic fields, have a high intrinsic gain (about 10 6) and operate at low voltages (40 V), eliminating the need for sophisticated shielding and low noise preamplifiers. A prototype 1×1 mm 2 detector currently under investigation at the University of Toronto consists of an array of 556 independent microcells operating in Geiger mode. Each microcell thus produces a pulse of constant amplitude with the detection of one or more electrons. All microcells are connected in parallel through integrated quenching resistors, and thus the output of the SiPM is the sum of the individual standardized signals and is proportional to energy provided the number of detected light photons is less than the number of microcells. The detector was operated without a preamplifier, and using a 2×2×6 mm 2 LSO crystal and 22Na source, the energy resolution was measured to be 25.6±0.4% FWHM and timing resolution for a detector pair was 1.9±0.1 ns FWHM. LED measurements and measurements using 133Ba (356 keV) and 137Cs (662 keV) verify that the detector is operating linearly at 511 keV. The major noise contribution is the dark current, which at −44 V results in a peak dark count rate of about 16 kHz that reduces to negligible levels above a 90 keV lower energy threshold. In the next generation of compact multi-element SiPM detectors with improved optical coupling the energy resolution should improve to below 15% FWHM, making them well suited for use in a high performance MR compatible depth of interaction PET scanner.

Study of beam heating effect in a gas target through Rutherford scattering

A systematic study of α -beam heating effect on a windowless gas target through Rutherford scattering is described. For such measurements, an ion implanted commercial silicon detector to reveal 100–250 keV alphas is used coupled with a low-noise home-made preamplifier. The results on density reduction of the gas in the target due to beam heating are discussed and their importance for high precision cross section measurements at very low energies are underlined.

High throughput measurements of soft x-ray impurity emission using a multilayer mirror telescope

A 4in. multilayer mirror telescope has been tested on National Spherical Torus Experiment (NSTX) for high throughput measurements of the beam excited soft x-ray impurity emission. The design is aimed at imaging low-k turbulent fluctuations in the plasma core. The test device used curved and planar Mo∕Si mirrors to focus with ≈15% optical transmission and few angstrom bandwidths, the 135Å Lyα line from injected Li III atoms, or the n=2–4 line from intrinsic C VI ions. As test detectors we used 1cm2 absolute extreme ultraviolet diodes, equipped with 400kHz bandwidth, low noise preamplifiers. With the available view on NSTX the telescope successfully detected small impurity density fluctuations associated with 1∕1 modes rotating at midradius, indicating that a high signal to noise ratio and cost effective core turbulence diagnostic is feasible based on this concept.

An Advanced Preamplifier for Highly Segmented Germanium Detectors

We present a fast low-noise hybrid charge-sensitive preamplifier for germanium position-sensitive gamma-ray detectors. In conjunction with a bulky 36-fold segmented detector it provided an excellent resolution of 1.71/1.77 keV fwhm on the 1.17/1.33MeV60Co lines. The preamplifier rise time, as measured at the test bench, is as fast as 7.5 ns, with a detector capacitance of 21 pF and with a 5 m 50 Omega twisted-pair cable connected at its output. The dynamic range of the preamplifier input stage is as large as 92 dB, ranging from 0.275 fC to 9.9 pC, i.e., from 5 keV to 180 MeV in terms of photon energy. On signals larger than 2 MeV a fast reset (~ 10 MeV/mus) is enforced to reduce the system dead time. An estimate of the amplitude of such large signals is derived from the reset time, still obtaining a high resolution. Using this technique we achieved an energy resolution of 0.3% at 16.7 MeV

An 8-Channel DRAGO Readout Circuit for Silicon Detectors With Integrated Front-End JFET

We have developed a CMOS circuit to be used with Silicon Drift Detectors (SDDs) for X-ray spectroscopy and gamma-ray imaging applications. The circuit operates with the input transistor integrated directly on the detector wafer. The circuit is composed of 8 analog channels, each including a low-noise voltage preamplifier, a 6th order semi-Gaussian shaping amplifier, with four selectable peaking times from 1.8 mus up to 6 mus, and a peak stretcher. The integrated time constant used for the shaping are implemented by means of a recently proposed 'RC' cell. This cell is based on the de- magnification of the current flowing in a resistor R thanks to the use of current mirrors. The 8 analog channels of the chip are multiplexed to a single analog output. A digital section provides self-resetting of the channels, trigger output and the external programming of independent threshold on the analog channels by means of a 3 bit DAC and a programmable serial register. In this work, the main features of the circuit are described. The measurement results obtained in the characterization of the prototype are then reported and discussed. The energy resolution measured using a single channel of the chip with a Silicon Drift Detector Droplet (SDD3) is of 128 eV at 6 keV with the detector cooled at -20degC. Spectroscopy measurements using a multi-element SDD are also shown

Microcontroller-Based Wireless Recording Unit for Neurodynamic Studies in Saltwater

This paper presents the design of a biocompatible implantable neural-recording unit for Aplysia californica, which is a common sea slug. Low-voltage extracellular neural signals (<250 muV) are recorded using a high-performance low-power low-noise preamplifier that is packaged with programmable digital data acquisition and control, and frequency-shift keying (FSK) telemetry that provides 5-kb/s wireless neural data through 18 cm of saltwater. The telemetry utilizes an 8-cm electric-dipole antenna matched to 50 Omega by exposing the ends of the antenna to the saltwater. A custom 27-MHz receiver has been developed using commercially available ICs. A clock data recovery algorithm is implemented in a microcontroller to synchronize the received data. A 3-V lithium-ion battery (160 mAh) allows 16 h of recording. Neural data obtained using extracellular nerve electrodes and a wired interface to this unit exhibit a 2.5-mV-rms noise, which is comparable to a commercial neural-recording equipment. Neural data were also collected through the wireless link, demonstrating the feasibility of low-power transmission through saltwater

Polarization fluctuations near the glass transition

Measurements of polarization fluctuations were performed for an epoxy glass former. The voltage noise produced by polarization fluctuations of the sample filling a capacitor was acquired via a home-made very high input impedance current–voltage converter, in series with an ultra low noise pre-amplifier, achieving high sensitivity and accuracy in the range 0.1–1000Hz. The temperature and frequency dependence of polarization noise was investigated above and below the glass transition temperature Tg. The sample was driven to the glassy state with different cooling rate and then isothermally aged, while the noise spectral density was measured at different times and compared with the Johnson–Nyquist noise determined by the sample impedance measured by conventional dielectric spectroscopy. At thermodynamic equilibrium the polarization noise agreed with the predictions of the fluctuation–dissipation theorem linking noise spectral density to susceptibility. On the contrary, a strong violation of the theorem was observed after a fast cooling below Tg: an intense polarization noise was detected, with a power spectral density following an inverse power law frequency behavior, whose intensity was decreasing with aging time. At the same time, the amplitude of polarization fluctuations showed a non-Gaussian distribution, whose width reduced during the aging process, up to recover the Gaussian statistics on approaching the equilibrium.

An eight channel low-noise CMOS readout circuit for silicon detectors with on-chip front-end FET

We propose a CMOS readout circuit for the processing of signals from multi-channel silicon detectors to be used in X-ray spectroscopy and γ-ray imaging applications. The circuit is composed by eight channels, each one featuring a low-noise preamplifier, a 6th-order semigaussian shaping amplifier with four selectable peaking times, from 1.8 up to 6 μs, a peak stretcher and a discriminator. The circuit is conceived to be used with silicon detectors with a front-end FET integrated on the detector chips itself, like silicon drift detectors with JFET and pixel detectors with DEPMOS. The integrated time constants used for the shaping are implemented by means of an RC-cell, based on the technique of demagnification of the current flowing in a resistor R by means of the use of current mirrors. The eight analog channels of the chip are multiplexed to a single analog output. A suitable digital section provides self-resetting of each channel and trigger output and is able to set independent thresholds on the analog channels by means of a programmable serial register and 3-bit DACs. The circuit has been realized in the 0.35 μm CMOS AMS technology. In this work, the main features of the circuit are presented along with the experimental results of its characterization.

A CMOS Readout Circuit for Silicon Drift Detectors With on-Clip JFET and Feedback Capacitor

We propose a CMOS circuit designed to be used with silicon drift detectors (SDDs) for high-resolution and high peak stability X-ray spectroscopy. The circuit is developed in the framework of a project for researches on exotic atoms (e.g., kaonic hydrogen) at e-/e+ colliders. The circuit is composed by a low-noise charge preamplifier, by a sixth-order semi-Gaussian shaping amplifier with four selectable peaking times from 0.7 mus up to 3 mus, and by a bipolar shaping amplifier to provide a timing signal required by the experiment. The preamplifier operates with the input JFET directly integrated on the detector itself. A low-frequency current-mode feedback loop allows to stabilize the operating point of the input JFET with respect to background and leakage current variations. The feedback capacitor is also integrated on the detector. Because its value is not known precisely a priori, the preamplifier is designed with the possibility to adjust externally its decay time to match the fixed time constant of the pole/zero network. A baseline holder senses the baseline voltage shifts at the output of the circuits due to the dc changes of the drain voltage of the input JFET in correspondence of background variations and provides a feedback loop back to the preamplifier to stabilize the output baseline. A first prototype has been realized in the 0.35-mum AMS technology. The energy resolution measured using the chip with a SDD of 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is of 137 eV at 6 keV (ENC=8 e-rms)

Experimental characterization of collapse-mode CMUT operation

This paper reports on the experimental characterization of collapse-mode operation of capacitive micromachined ultrasonic transducers (CMUTs). CMUTs are conventionally operated by applying a direct current (DC) bias voltage less than the collapse voltage of the membrane, so that the membrane is deflected toward the bottom electrode. In the conventional regime, there is no contact between the membrane and the substrate; the maximum alternating current (AC) displacement occurs at the center of the membrane. In collapse-mode operation, the DC bias voltage is first increased beyond the collapse voltage, then reduced without releasing the collapsed membrane. In collapse-mode operation, the center of the membrane is always in contact with the substrate. In the case of a circular membrane, the maximum AC displacement occurs along the ring formed between the center and the edge of the membrane. The experimental characterization presented in this paper includes impedance measurements in air, pulse-echo experiments in immersion, and one-way optical displacement measurements in immersion for both conventional and collapse-mode operations. A 205-microm x 205-microm 2-D CMUT array element composed of circular silicon nitride membranes is used in the experiments. In pulse-echo experiments, a custom integrated circuit (IC) comprising a pulse driver, a transmit/receive switch, a wideband low-noise preamplifier, and a line driver is used. By reducing the parasitic capacitance, the use of a custom IC enables pulse-echo measurements at high frequencies with a very small transducer. By comparing frequency response and efficiency of the transducer in conventional and collapse regimes, experimental results show that a collapsed membrane can be used to generate and detect ultrasound more efficiently than a membrane operated in the conventional mode. Furthermore, the center frequency of the collapsed membrane can be changed by varying the applied DC voltage. In this study, the center frequency of a collapsed transducer in immersion is shown to vary from 20 MHz to 28 MHz with applied DC bias; the same transducer operates at 10 MHz in the conventional mode. In conventional mode, the maximum peak-to-peak pressure is 370 kPa on the transducer surface for a 40-ns, 25-V unipolar pulse excitation. In collapse mode, a 25-ns, 25-V unipolar pulse generates 590 kPa pressure at the surface of the transducer.

A low-cost, ultra-fast and low-noise preamplifier for micro channel plates

A compact, low-cost, ultra fast, low distortion and low noise preamplifier suitable for data-acquisition applications utilization micro channel plate (MCP) detectors has been built with a new monolithic integrated circuit amplifier in two stages. The gain, bandwidth and noise are optimized to the MCP performance in order to achieve the best rise time, response and stability with minimal jitter. The use of commercial components makes this instrument very low in cost and easy to build.

Low-noise amplification of /spl gamma/-ray detector signals in hostile environments

We designed and realized a low-noise charge preamplifier for HPGe (High Purity Germanium) /spl gamma/-ray detectors, able to operate at a distance of 3 m to 6 m from the detector. One transistor only is placed in close proximity to the detector. Such a setup is required in applications where the detector works in hostile environments that could damage or destroy the electronic circuitry. Using 3 m RG62 cables and a 23 pF detector capacitance we obtained a noise of /spl sim/1.07 keV fwhm at 2 /spl mu/s shaping time, so fully compatible with /spl gamma/-spectroscopy requirements. By compensating the preamplifier so as to completely eliminate the ringing in its response function we obtained a rise-time of /spl sim/46 ns with 3 m cables and of /spl sim/80 ns with 5 m cables. With a different approach, or using a lower compensation capacitance and eliminating the ringing through a numerical post filter, we obtained a faster rise time of /spl sim/33 ns, with a detector-preamplifier distance of 5 m, while maintaining the low-noise performance. This latter setup is adequate for spectroscopy and tracking of /spl gamma/-rays with segmented HPGe detectors.