Spectrum analyzer with noise reduction by cross-correlation technique on two channels

A spectrum analyzer with a sensitivity better than few pV/root Hz in voltage noise measurements and better than 1 fA/root Hz in current noise measurements is presented. It has two distinct and independent input amplifiers in parallel, connected to the same device under test (DUT) and is based on the suppression of their uncorrelated noises. The instrument is modular with different front-end amplifiers conceived to optimize the measurement of low impedance or high impedance DUTs. The instrument can cover 8 decades of frequency span, from 10 mHz to 1 MHz. The improvement of sensitivity with respect to a traditional system and the simplicity in the connection and biasing of the DUT makes it perfectly suited to measure ultralow noise levels in semiconductor devices, like trapping noise, shot noise associated with tunneling in fractional quantum Hall systems, 1/f and channel noise in metal-oxide-semiconductor field effect transistors operated below threshold. ()C 1999 American Institute of Physics. [S0034-6748(99)01805-5].