Cross-correlation on a single channel for resistance noise measurements

Cross-correlation is an established tool to reduce the background in resistance noise measurements. However, the conventional method requires the amplifier, demodulator and digitizer channels to be duplicated, increasing the cost and complexity of the measurement circuit. We propose an alternating-current technique that allows cross-correlation with only a single channel by modulating the device under test with two carrier frequencies simultaneously. Using multiple software-based demodulators, we show that this method produces accurate amplitude measurements and noise spectra. The signal-to-noise-ratio is improved by 7 decibel for standard parameters. Longer measurement durations increase this improvement, which makes the new technique a true cross-correlation method.