Multichannel Amplifier Topologies for High-Sensitivity and Reduced Measurement Time in Voltage Noise Measurements

In this paper, we discuss a few techniques that allow an effective reduction of the background noise and/or the reduction of the measurement time when performing voltage noise measurements by employing a number of nominally identical voltage amplifiers with negligible equivalent input current noise. It is demonstrated in particular that, if N (N > 2) voltage amplifiers are connected to the device under test and if the properties of cross-correlation among all N acquisition channels connected to the output of each amplifier are exploited, the time required for obtaining a given accuracy is reduced by a factor N(N - 1)/2 with respect to the conventional setup for cross-correlation that employs only two channels. From another point of view, the effective background noise is reduced for constant measurement time. Such a factor can be further increased if amplifier paralleling is also employed for reducing the equivalent input voltage noise for each channel. Measurements on two different setups employing up to four channels and up to eight channels are presented that confirm the expected reduction factors in measurement times.