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Register a new userA Transimpedance Amplifier for Remotely Located Quartz Tuning Forks
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The cable capacitance in cryogenic and high vacuum applications of quartz tuning forks imposes severe constraints on the bandwidth and noise performance of the measurement. We present a single stage low noise transimpedance amplifier with a bandwidth exceeding 1 MHz and provide an in-depth analysis of the dependence of the amplifier parameters on the cable capacitance.
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A transimpedance amplifier has been designed for scanning tunneling microscopy (STM). The amplifier features low noise (limited by the Johnson noise of the 1 G{Omega} feedback resistor at low input current and low frequencies), sufficient bandwidth for most STM applications (50 kHz at 35 pF input capacitance), a large dynamic range (0.1 pA--50 nA without range switching), and a low input voltage offset. The amplifier is also suited for placing its first stage into the cryostat of a low-temperature STM, minimizing the input capacitance and reducing the Johnson noise of the feedback resistor. The amplifier may also find applications for specimen current imaging and electron-beam-induced current measurements in scanning electron microscopy and as a photodiode amplifier with a large dynamic range. This paper also discusses the sources of noise including the often neglected effect of non-balanced input impedance of operational amplifiers and describes how to accurately measure and adjust the frequency response of low-current transimpedance amplifiers.
The performance of a muon radiography system designed to image the inner structure of a nuclear plant located at a distance of 64 m was evaluated. We concluded absence of the fuel in the pressure vessel during the measurement period and succeeded in profiling the fuel material placed in the storage pool. The obtained data also demonstrated the sensitivity of the system to water level changes in the reactor well and the dryer-separator pool. It is expected that the system could reconstruct a 2 m cubic fuel object easily. By operating multiple systems, typically four identical systems, viewing the reactor from different directions simultaneously, detection of a 1 m cubic object should also be achievable within a few month period.
We have developed a new capacitive transimpedance amplifier (CTIA) that can be operated at 2 K, and have good performance as readout circuits of astronomical far-infrared array detectors. The circuit design of the present CTIA consists of silicon p-MOSFETs and other passive elements. The process is a standard Bi-CMOS process with 0.5$mu$m design rule. The open-loop gain of the CTIA is more than 300, resulting in good integration performance. The output voltage swing of the CTIA was 270 mV. The power consumption for each CTIA is less than 10$mu$W. The noise at the output showed a$1/rm f$noise spectrum of 4$mu$V/$surdhbox Hz$at 1 Hz. The performance of this CTIA nearly fulfills the requirements for the far-infrared array detectors onboard ASTRO-F, Japanese infrared astronomical satellite to be launched in 2005.
We present the design and characterisation of a low-noise, resonant input transimpedance amplified photodetector. The device operates at a resonance frequency of $90 ,textrm{MHz}$ and exhibits an input referred current noise of $1.2,textrm{pA}/sqrt{textrm{Hz}}$---marginally above the the theoretical limit of $1.0,textrm{pA}/sqrt{textrm{Hz}}$ set by the room temperature Johnson noise of the detectors $16,textrm{k}Omega$ transimpedance. As a result, the photodetector allows for shot-noise limited operation for input powers exceeding $14,mutextrm{W}$ at $461,textrm{nm}$ corresponding to a noise equivalent power of $3.5,textrm{pW}/sqrt{textrm{Hz}}$. The key design feature which enables this performance is a low-noise, common-source JFET amplifier at the input which helps to reduce the input referred noise contribution of the following amplification stages.
The National High Magnetic Field Laboratory (NHMFL) High B/T facility at the University of Florida in Gainesville provides a unique combination of ultra-low temperatures below 1 mK and high magnetic fields up to 16 T for user experiments. To meet the growing user demand for calorimetric and thermal transport measurements, particularly on milligram-sized solid samples, we are developing scaleable thermometers based on quartz tuning fork resonators immersed in liquid $^3$He. We demonstrate successful thermometer operation at the combined extreme conditions available at our user facility, and discuss the feasibility of fast and compact thermal probes.
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