Noise reduction of spin torque oscillator by phase-locked loop with combinational frequency tuning method

The noise of a spin torque oscillator (STO) is 4-6 orders higher than that of a traditional CMOS Voltage Controlled Oscillator (VCO). This is the biggest obstacle hindering the STO to replace the VCO in pragmatic usage since a high quality RF signal is essential to the modern telecommunication system. The phase-locked loop (PLL) is widely used in RF chips, which can both stabilize VCO frequency and reduce its noise. There are very few experimental and theoretical works investigating the STO stabilized by the PLL, whereas the numerical investigation is totally missing. In this work, the STO stabilized by the PLL is numerically investigated. Based on the analysis, a combinational frequency tuning method is proposed, which is suitable for the PLL operation and can reduce the STO noise even further.