Low-temperature preamplifier

摘要

A method and apparatus for amplifying low-level electrical signals at low temperatures (typically below 4.2 K) is disclosed. The problem of large heat dissipation ( APPROX mW) in cryogenic amplifiers (1, 2, 8) is solved. A low-temperature section (3) comprises a field-effect transistor or FET (1) and an elevated temperature section comprises current sensing means (2), such as an operational amplifier or op-amp (2). According to the invention the FET (1) is operated in the small-signal ohmic regime. Thereby ultra-low power losses in the FET (1) (e. g. below APPROX 1 nW) are achieved. One or several FETs (1) can be mounted inside a cryostat close to a measuring impedance (ZTF) with negligible heating of the cryostat. A particular stable operation of the FET (1) in the ohmic regime and a selectable operating point are realized by supplying a constant source-drain voltage USD (e. g. 1 mu V - 100 mV) and a separately adjustable gate-drain voltage UGD. An amplifier (1, 2, 8) for implementing the method and a scanning probe microscope comprising the amplifier (1, 2, 8) are disclosed as well. <IMAGE> <IMAGE>