An analysis of a measurement probe for a high impedance spectroscopy analyzer

The paper presents a measurement probe which forms the input circuitry of an analyzer for high impedance spectroscopy. The probe allows measurements of impedance which is grounded at one terminal in the range of 100 Ω < ∣Zm∣ ⩽ 100 GΩ. It extracts two signals proportional to current through and voltage across the measured impedance in a wide frequency range from 100 μHz up to 100 kHz. An analysis of the probe has been performed taking into account the most important parameters affecting the accuracy of the impedance measurement: parasitic capacitance at the probe input, the parameters of the transfer function of the amplifier and the tolerance of the resistors in the differential amplifier of the current signal. The formula for determining the measured impedance was elaborated, taking into consideration corrections minimizing the influence of the parasitic capacitance and the real-life parameters of the operational amplifiers.