Loading effect of the AC-DC transfer standard for low level AC voltage standard

AC-DC transfer standard and micro-potentiometer are widely used for AC voltage standard at low level. Input impedance and 50-Ω load dependency of the standard are discussed for the ac voltage application below 200 mV and 1 MHz. The load dependency of the unit reaches 385 µV/V at 1 MHz, and this loading error should be corrected when calibrate the 50-Ω AC source using the standard.