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Ultra-low-noise preamplifier

Licence available
Especially interesting for
  • cryoelectronics
  • cryophysics

The ultra-low-noise preamplifier developed by PTB considerably reduces measurement uncertainties, e. g., for the traceability of impedance standards. This preamplifier is characterized by the fact that selected field effect transistors are connected in parallel at the input; these have the lowest possible noise current and noise voltage values. The circuit is designed in such a way that a stable standby current is generated by the input transistors and also that the drain resistance is increased dynamically. In this way, the noise of the pre-stage can be optimally adapted to that of the main stage. This guarantees very low noise. The optimized feedback network adjusts a stable gain. This novel circuit concept enables the so far unprecedented combination of an input noise voltage smaller than 0.5 nV, an input noise current smaller than 5 fA and an input impedance of 1 GΩ parallel to approx. 100 pF (stated for a noise bandwidth of 1 Hz at a measuring frequency of 1 kHz).


Günther Ramm,
Department 2.1 Direct Current and Low Frequency
phone: +49 (0) 531 592-2190
e-mail: guenther.ramm(at)ptb.de