磁気シールドを施した前置増幅器を用いた微小電圧計測

抄録

For measurement of nano-voltages it is required to evaluate the noise which comes from a Zener diode and a lithium battery which will be used here.
This paper discusses the problems which arise when a commercial digital multimeter (D.M.M.) which has nominally resolution of 10nV is used for some measurement. That is, the magnetic fields in a usual test room which is 10^-9 to 10^-7 T with 60Hz and also the magnetic field which is 10^-7 T and comes from the power supply part of the D.M.M. through the transformer will disturb nano-volt measurement. These magnetic fields possibly induce a 10nV in the measurement circuit of the D.M.M. This fact recommends the magnetic shielding of the measurement circuit. Moreover the D.M.M. shows 10∼20μV when the input terminals are short circuited. This fact is very a serious problem for measurement of nano-volt. We observed that linearity is not hold lower than 800nV using a single frequency sinusoidal voltage input.
In order to resolve the problems mentioned above, a measured voltage is pre-amplified by a low-noise amplifier with magnetic shielding before it is input to the D.M.M. As a result, the lowest linearity improved from 800nV to 10nV is obtained.