Low-Frequency Noise Measurement of High-Ohm Resistors

This paper addresses with the measurement of low-frequency noise in high-ohm resistors. The magnitude of low-frequency 1/f noise is primarily determined by the manufacturing technology of the resistor. In this paper, the noise of precise thick-film resistors was compared with the noise of metal-oxide resistors, which, according to theory, should generate very low low-frequency noise. For this purpose, new measuring equipment was developed to provide accurate results by correlating its two outputs. Another method used in this paper was the conversion of the noise-voltage spectral density from measured time histories. This method can be used to measure a wide frequency range at high voltage drop on resistors. The low-frequency noise of thick-film resistors was compared based on the size of their packages and the magnitudes of their voltage coefficient. A combination of both methods can provide very accurate results. The main reason for this measurement was to select high-quality, high-ohm resistors for measuring very small currents in order of pA and fA, where there is often no alternative to thick-film resistors. Their 1/f low-frequency noise is often not specified by the manufacturer.