A 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.

Automatic offset cancellation and time-constant reduction in charge-sensitive preamplifiers / A. Pullia, F. Zocca. - In: IEEE TRANSACTIONS ON NUCLEAR SCIENCE. - ISSN 0018-9499. - 57:2(2010 Apr), pp. 5409506.732-5409506.736. [10.1109/TNS.2009.2038913]

Automatic offset cancellation and time-constant reduction in charge-sensitive preamplifiers

A. Pullia
Primo
;
2010

Abstract

A 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.
charge preamplifier ; low noise preamplifier ; offset ; semiconductor detector
Settore ING-INF/01 - Elettronica
apr-2010
Article (author)
File in questo prodotto:
Non ci sono file associati a questo prodotto.
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/152344
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 14
  • ???jsp.display-item.citation.isi??? 7
social impact