NEW CONCEPT OF A MEASUREMENT PROBE FOR HIGH IMPEDANCE SPECTROSCOPY

The paper presents a new measurement probe working as the input circuit for a high impedance spectroscopy analyzer. The probe allows to measure impedance in the range of 100 Omega < vertical bar Z(x)vertical bar < 100 G Omega. The probe extracts two signals proportional to current through and voltage across the measured impedance in a wide frequency range from 100 mu Hz to 1 MHz. By the use of a current-to-voltage converter the influence of capacitance of the shielded cables connecting the object under measurement on the result of the measurement is kept as low as possible. An analysis of the probe has been performed taking into account most important parameters influencing the measurement accuracy: parasitic capacitance and real-life parameters of operational amplifiers in use. The formula for calculation of the modulus and argument of the measured impedance has been developed taking into account the correction for real-life parameters of the probe. This allows to decrease the maximal measurement errors of the impedance modulus to ca. 1% and of the impedance argument to 2 degrees, respectively, in the whole range of measurement frequencies.