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Low-current amplifier for practical calibration and for quality assurance


Generating and measuring extremely small electric currents down into the range of femtoamperes (10–15 ampere) are gaining in importance.

Low-current amplifier for practical calibration and for quality assurance

Developing and monitoring the production of highly integrated circuits, dosimetry in radiation protection, the detection of ultra-low concentrations in environmental measuring techniques, DNA sequencers and the measurement of photoelectric currents in the lighting industry are examples of this. In order to provide the required measurement and calibration technology in the future, “single-electron circuits” are being developed both at PTB and worldwide. These systems are used to link up the unit of electric current to the elementary charge of an electron by “counting” single electrons. Such systems must, however, be operated in the millikelvin range.

At PTB, a handy, table-top device which is based on a different principle has been developed. It is designed for operation at room temperature in calibration laboratories. With this device, it is possible to attain nearly the same accuracy as with a singleelectron source. With regard to its characteristics, it is superior to all conventional, commercially available low-current measuring instruments which are, for the major part, currently supplied by US manufacturers.

This novel instrument combines the following features:

  • current measuring range from femto- to microamperes (fA – μA)
  • at the same time reference current source for currents from femto- to microamperes
  • very low relative measurement uncertainty (0.1 ppm at a current of 100 pA)
  • vast application range for “next-generation” current calibration, e.g. Industry 4.0 sensors technologies.

Within the scope of a technology transfer program, PTB’s new development was transferred, together with two patent applications, to a small German enterprise, Magnicon GmbH, Hamburg. The instrument has been produced and commercialized under PTB license under the designation “ULCA” (short for Ultrastable Low-noise Current Amplifier) since mid-2016. The first instruments have already been delivered to calibration laboratories and national metrology institutes.</l&