1,721,012 research outputs found
Automatic offset cancellation and time-constant reduction in charge-sensitive preamplifiers
No full textA circuit technique is presented which eliminates the offset at the output of charge-sensitive preamplifiers and optionally reduces the resistive reset time-constant. Offset cancellation as well as time-constant reduction are obtained with no trimming. Offset cancellation is obtained actively through a negative feedback path whose "error" variable is the offset itself. As a result the output voltage offset is automatically eliminated, irrespective of the bias point of the input transistor and the dark current of the sensor connected to the preamplifier. Using the proposed technique in low-noise charge preamplifiers for germanium detectors typical offsets in the range 100-300 mV are reduced to +/-2 mV. The noise of the preamplifier is unaffected by the offset cancellation circuit. Moreover, by insertion of an optional resistor in the proposed circuitry the decay time-constant of the preamplifier is automatically reduced by a factor of up to 10, while leaving unchanged the noise and the sensitivity of the charge preamplifier. This improves pulse separation at the preamplifier's output, which can be particularly useful for pattern recognition at high event rates. The realized offset-free circuit features an equivalent noise of 650 eV fwhm in germanium at 3 mu s shaping time, i.e. an Equivalent Noise Charge of similar to 94 electrons r.m.s. and a dynamic range in excess of 86 dB, which makes it perfectly suited for high-resolution gamma-ray spectrometry with large germanium detectors
Low-noise current preamplifier for photodiodes with DC-current rejector and precise intensity meter suited for optical light spectroscopy
No full textA low-noise large dynamic-range current preamplifier for photodiode current signals is presented. The circuit is equipped with a smart device for automatic removal of the DC current of the photodiode. This device sinks away the exact amount of DC current from the preamplifier input, yielding auto zeroing of the output-voltage offset, while introducing the minimum electronic noise possible. As a result the measurement dynamic-range is maximized. An auxiliary inspection point is provided which precisely tracks the DC component of the photodiode current. This auxiliary signal may be used for precise beam alignment and diagnostic purposes. The excellent gain stability and linearity make the circuit perfectly suited for optical-light pulse spectroscopy. Applications include two-dimensional characterization of semiconductor detectors, ultra-precise characterization of laser beam stability, particle sizing in the 100 nm range, confocal microscopy
Preamplificatore a transimpedenza per fotorivelatori con indicatore preciso di intensità
No full textLa presenza di una corrente stazionaria nel fotorivelatore (illuminato) rende difficile la misura dei piccoli segnali ad essa sovrapposti e tende a ridurre molto significativamente il range dinamico delle misure. L’invenzione consiste in un circuito preamplificatore di tali segnali, che sopprime automaticamente l’offset dovuto alla corrente stazionaria sottostante introducendo un rumore elettronico aggiuntivo trascurabile, e fornendo in una apposita uscita una misura ultra-precisa della corrente stazionaria del fotodiodo.
Caratteristiche dell’invenzione: completa reiezione alla corrente stazionaria del fotorivelatore illuminato e contestuale presenza di un indicatore ultra-preciso della intensità di tale corrente stazionaria. Ciò senza aumento di rumore elettronico né calo di guadagno, range dinamico e banda passante
Metodo e dispositivo per la misura di segnali generati da un rivelatore di particelle e⁄o radiazioni ionizzanti
No full textViene descritto un metodo per la misura di segnali generati da un rivelatore di particelle e/o radiazioni ionizzanti, detti segnali essendo resi disponibili alle uscite del rivelatore sotto forma di cariche elettriche, comprendente i passi di: rimuovere tutte dette cariche elettriche a tasso costante da dette uscite del rivelatore; misurare il tempo necessario per la rimozione di tutte dette cariche elettriche; convertire detto tempo in una misura della quantità di dette cariche elettriche
A low-noise preamplifier for gamma-ray sensors with add-on device for large-signal management
No full textA new charge-sensitive preamplifier for High Purity Germanium gamma-ray detectors has been built and tested. It comprises an over-load recovery device that reduces the dead time brought about by hits of energetic particles. The amplitude of the large signals is reconstructed from Time-Over-Threshold measurements performed along the reset transients. Using such a technol. an extremely wide energy range of 10 keV to 30 MeV, or 70 dB, is obtained. With a count rate of 6 kHz a resoln. of 1.1 keV fwhm is obtained on the 152Eu 122 keV line and of .apprx.5 perthousand on pulser lines in the energy range of 5-30 MeV
De-oscillating preamplifier signals through digital filtering techniques
No full textWe present a time-domain digital filtering technique able to eliminate the ringing of preamplifier signals. The preamplifier signal is sampled by an ADC and then processed by a digital filter, whose aim is to eliminate the ringing while minimizing the loss of high-frequency information. We developed such a filtering technique for the case of a charge-sensitive preamplifier for gamma-ray spectroscopy installed far away from the detector/FET cryogenic assembly. With such a setup a damped oscillation is caused by the long connection cable acting as a delay line along the feedback loop. We could completely eliminate the ringing in the output signals and maintain, at the same time, a large bandwidth and a high loop gain. Experimental results are shown
An auto-zero charge preamplifier with "cold" discharge mechanism for ionising radiation sensors
No full textA circuit technique is presented which eliminates the offset error in the output voltage of low-noise charge preamplifiers for ionising radiation sensors. Offset cancellation is obtained actively through a negative feedback path whose “error” variable is the offset itself. As a result the output voltage offset is automatically eliminated with no trimming, irrespective of the bias point of the input transistor and the dark current of the sensor. Using the proposed technique in a low-noise charge preamplifier for germanium detectors we obtained an output voltage offset < 1 mV against an original offset of -291 mV. The output offset of these preamplifiers is typically in the range of -500 mV to +100 mV, as mainly dictated by the bias voltage of the gate of the input FET (Field Effect Transistor). The noise of the preamplifier is unaffected by the offset cancellation circuit. In addition, an optional resistor permits reduction of the the fall time of the preamplifier by a factor of 1 to 10, while leaving unchanged the noise and the sensitivity of the charge preamplifier. This helps reduce the pileup at high count rates
Fast low-impedance output stage for CMOS charge preamplifiers able to work at cryogenic temperatures
No full textThe quality of the output stage is key to the performance of low-noise CMOS preamplifiers for semiconductor detectors, especially when the preamplifier signal is to be transmitted to a remote receiver. This work deals with two implementations of an output-stage circuit architecture particularly suited for low-noise integrated preamplifiers of X and gamma-ray detector signals. The aim is to conjugate a few important features: low output impedance, ability to work at room and cryogenic temperatures, ability to drive a terminated coaxial cable, low power consumption, large voltage swing with a 100 ohm load. In particular we were interested to a large negative voltage swing. The standard solution, i.e. a source-follower stage realized with a p-MOSFET, is not adequate because its threshold and overdrive voltage would severely limit the negative output voltage swing. The proposed circuit structure, inspired to the White follower, builds around a first n-MOSFET configured as source follower, a second n-MOSFET acting as driver for the load current and a negative-feedback loop which stabilizes the working current of the first MOSFET. As a result both a low output impedance and a large negative voltage swing are obtained. Using a prototype of such output stage in a JFET-CMOS charge-sensitive preamplifier for germanium detectors we obtained a large negative voltage swing, a signal rise time of ~13 ns with a resistive load of 100 ohm, and a negligible additional noise
Design criteria for the optimization of hybrid charge-sensitive preamplifiers for high resolution gamma-ray spectroscopy
No full textDesign criteria for the optimization of hybrid charge-sensitive preamplifiers for germanium high resolution gamma-ray detectors are presented. In particular we studied the optimization of the Transimpedance Amplifier (T.A.) following the input JFET and realized with Bipolar Junction Transistors. Our aim was to highlight and adjust the key parameters of the T.A. in order to maximize the loop gain of the charge-sensing stage while maintaining at the same time an adequate low noise. We analytically studied the expression of the open-loop gain, focusing our attention on the upper limit that can be reached according to the physical parameters of the chosen devices. We analyzed the role played by the Miller effect acting on the input JFET gate-drain capacitance, which reduces the loop gain of the charge-sensing stage, and we proposed a solution to address this issue. We studied the optimization of the folded cascode BJT bias current in order to minimize the T.A. noise. Analytical study is reported and simulation results for typical structures are shown
Optimization of a time-over threshold preamplifier for high-purity germanium detectors
No full textThis paper deals with the optimization of a new time-variant preamplifier for High Purity Germanium (HPGe) detectors, featuring an unprecedented 90dB dynamic range in high resolution spectrometry of ionizing particles/radiations. The preamplifier works with a conventional resistor reset for gamma photon energies < 3 MeV while it uses a pulsed fast reset for large pulses of higher energies. The height of the large pulses is measured indirectly from the preamplifier reset time using a Time-over-Threshold (ToT) measurement technique, which is effective even when the signal is much larger than the input voltage swing of the Analog to Digital Converter (ADC). This yields a substantial increase of the overall measurement dynamic range. We studied the time jitter of the ToT parameter by using the concept of “Noise Weighting Function” (NWF). We found that the limiting factor for the signal-to-noise ratio of the ToT measurement comes from the steepness of the NWF’s slope at a certain time position. By smoothing out the NWF’s corner by simply using a passive RC network we were able to improve the time jitter of the ToT measurement of as much as 50%, or from 610 ps to 305 ps (r.m.s.). A noise correlation property is finally observed, which can be used to cancel in part the noise and so improve the spectroscopic resolution in the ToT mode. A detailed study of the ToT technique and its performance is presented in this paper
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