Influence of Thermal Noise on the Frequency Resolution of a Sweep-Tuned Spectrum Analyzer

Nano-sized spin-torque nano-oscillators (STNO) can be very rapidly sweep-tuned by variation of the bias direct current, and, therefore, can be used in ultra-fast (tuning speed ~100 MHz/ns) sweep-tuned spectrum analyzers [1,2]. At relatively high tuning speeds the resolution in frequency determination in such a device is determined by the bandwidth theorem. In contrast, at a relatively low tuning speed the generation linewidth of the STNO, which is determined by the thermal noise, is the limiting factor in the frequency determination accuracy. Our numerical calculations have shown that the external thermal noise not only leads to the broadening of the STNO generation linewidth, but also to the STNO central frequency “jitter”, which can significantly impact the accuracy of the frequency determination.

[1] S. Louis, O. Sulymenko, Vasil Tiberkevich, et al., Ultra-fast wide band spectrum analyzer based on a rapidly tuned spin-torque nano-oscillator, Appl. Phys. Lett. 113, 112401 (2018).
[2] A. Litvinenko, V. Iurchuk, P. Sethi, et al., Ultrafast Sweep-Tuned Spectrum Analyzer with Temporal Resolution Based on a Spin-Torque Nano-Oscillator, Nano Letters 20, 6104 (2020),
DOI: 10.1021/acs.nanolett.0c02195.