Low Power Microwave Signal Detection With a Spin-Torque Nano-Oscillator in the Active Self-Oscillating Regime

A spin-torque nano-oscillator (STNO) driven by a ramped bias current can perform spectrum analysis quickly over a wide frequency bandwidth. The STNO spectrum analyzer operates by injection locking to external microwave signals and produces an output dc voltage V dc that temporally encodes the input spectrum. We found, via numerical analysis with a macrospin approximation, that an STNO is able to scan a 10 GHz bandwidth in less than 100 ns (scanning rate R exceeds 100 MHz/ns). In contrast to conventional quadratic microwave detectors, the output voltage of the STNO analyzer is proportional to the amplitude of the input microwave signal I rf with sensitivity S = dV dc /dI rf ≈ 750 mV/mA. The minimum detectable signal of the analyzer depends on the scanning rate R and, at low R ≈ 1 MHz/ns, is about 1 pW.