C. Brofferio

Cryogenic voltage-sensitive preamplifier using GaAs MESFETs of low 1ƒ noise

Abstract A voltage-sensitive preamplifier using GaAs MESFETs of low 1 ƒ noise has been developed. The voltage gain is fixed to 51. With a total power dissipation of 54 mW the preamplifiers series noise level at 4 K is 9 nV / Hz 1 2 at 100 Hz and 0.3 nV / Hz 1 2 at 100 kHz. The input bias current of the preamplifier was determined to be lower than 10 fA below 100 K. Response to a step pulse gave a rise time of 40 ns when loaded with a 130 pF load. The voltage-sensitive preamplifier is presently used in Milano for signal readout and characterization of large-mass bolometric particle detectors. An energy resolution of 13 keV for the 1330 keV of a 60Co gamma source was obtained with an 11 g Ge bolometric detector readout with this preamplifier.

Gallium-arsenide charge-sensitive preamplifier for operation in a wide low-temperature range

A charge-sensitive preamplifier for temperature operation between 1 and 120 K has been developed and evaluated. It uses double-gate GaAs MESFETs selected for their low 1/ƒ noise. These devices are operated with both gates interconnected emulating single-gate MESFETs of double gate-length, obtaining in this way a value for Aƒ, the coefficient of the 1/ƒ noise spectral power density, of 1.7 × 10−13 V2 at 77 K and 3.8 × 10−14 V2 at 4 K. The latter is one fourth the value exhibited by the original device before modification and two orders of magnitude less than the value measured at 300 K. At the optimum bias operating point device transconductance is 6 mA/V, input capacitance is less than 5 pF and the power dissipation 360 μW. The circuit configuration consists of a double-cascade loaded with a bootstrapped current source. In this way, a high gain-bandwidth product is obtained despite of the low dynamic output resistance, 3000 Ω, exhibited by the MESFETs at the operating point. Equivalent noise charge was measured for detector capacitances up to 35 pF. Using a semi-Gaussian weighting function minimum values of 58 and 20 rmse− at 77 and 4 K, respectively, were determined. Noise slopes are 4.68 and 3.64 e−/pF at 1 μs shaping time for 77 and 4 K, respectively. A rise time of 20 ns was measured at the receiving-end of a 1 m length 50 Ω coaxial cable terminated at sending-end, when detector capacitance was CD = 35 pF. The total power dissipation of the preamplifier is less than 10 mW.

A programmable front-end system for arrays of bolometers

We report on a new front-end system developed to readout an array of large mass bolometers. The front-end allows setting all the necessary parameters for each detector by remote control. A special circuit, also red remotely, has been developed in order to adjust the output voltage, allowing the DC coupling to the detector. ( 2000 Elsevier Science B.V. All rights reserved.

A low DC drift read-out system for a large mass bolometric detector

We present a read-out solution for a bolometric detector of large mass. It consists of a voltage-sensitive preamplifier, having very low series and parallel input noise, thanks to the use of a pair of selected silicon JFETs at the input. Very good electrical characteristics were obtained. DC power supply rejection ratio, thermal drift of input offset voltage and input leakage current are minimized by using novel circuit solutions. Parallel noise behavior was also investigated using a new measurement method capable to be sensitive to shot noise generated by very small currents (tens of fA).

A front-end for an array of /spl mu/-bolometers for the study of the neutrino mass

We present a very low noise front-end solution for the readout of an array composed of 10 /spl mu/-bolometers. The system consists of a cold JFET and a room temperature second stage. The optimization of the second stage feedback configuration allowed to minimize the overall noise figure. A very simple current generator having a large output impedance has been developed and is used for biasing the cold JFET.

Signal modelling for TeO2 bolometric detectors

An energetic particle impinging a large mass bolometric detector generates signals of different shape depending on where the energy is deposited: in the absorber or in thethermal sensor. By exploiting this effect and the thermal characteristic of the sensor, all the parameters needed for simulating the dynamic behaviour of the detector for small and large signals were extracted. The model was used for simulating a series of 3 TeO2 bolometers with mass of 70g and 330g. For an accurate analysis an electric field effect dependance of the electron-phonon thermal conductance and electrons heat capacity in the thermistors used was taken into account. Also an interesting measured and simulated effect was considered regarding the quasi complete thermalized energy given by an α-particle.

A linear, low-noise, low-power optocoupler amplifier for bolometric detectors

We present an optocoupler with di⁄erential inputs and balanced output, which was realized to make galvanic decoupling in a bolometric detector read-out chain. The circuit configuration incorporates a true di⁄erential optocoupled feedback, with low bias current in LEDs and photodiodes. Large Common Mode (CMRR) and Power Supply (PSRR) Rejection Ratio, low crossover distortion, high dynamic range, low noise and power dissipation have been achieved. ( 1998 Elsevier Science B.V. All rights reserved.

Measuring thermistor resistance with very low d.c. power dissipation

Abstract A very simple and efficient procedure for measuring thermistor resistances at very low temperatures (down to 5 mK) with d.c. bias voltages is presented. The measurements can be performed with a d.c. power dissipation in the thermistors as low as 10 −18 W or less, as required by the extreme thermistor sensitivity to small heating effects. In particular this method suppresses the effects of the input current of the amplifier used for the measurement. We are using this procedure for the automatic characterization of thermistors with impedances up to 10 9 Ω at temperatures as low as 10 mK.

Cryogenic, monolithic, differential GaAs preamplifier for bolometric detectors

Abstract We present a first prototype of a monolithic differential voltage-sensitive preamplifier for cryogenic applications made in a GaAs ion implanted MESFET process. This preamplifier presents a very high input impedance using only a single long-tailed pair at its input, which allows the noise to be kept low. It was designed to obtain low power dissipation and a large dynamic range. The results of the first prototype chips are presented.

Large mass, low temperature, low background detectors

Abstract Bolometric detectors can be realized with a wide range of materials, and large mass. Some aspects regarding the energy resolution of large bolometers are analyzed. Preliminary experimental results on neutrinoless ββ decay of tellurium, obtained with this technique, are shown.