Abstract
Spin-torque nano-oscillators (STO) are candidates for the next technological implementation of spintronic devices in commercial electronic systems. For use in microwave applications, improving the noise figures by efficient control of their phase dynamics is a mandatory requirement. In order to achieve this, we developed a compact phase locked loop (PLL) based on custom integrated circuits (ICs) and demonstrate that it represents an efficient way to reduce the phase noise level of a vortex based STO. The advantage of our approach to phase stabilize STOs is that our compact system is highly reconfigurable e.g. in terms of the frequency divider ratio N, RF gain and loop gain. This makes it robust against device to device variations and at the same time compatible with a large range of STOs. Moreover, by taking advantage of the natural highly non-isochronous nature of the STO, the STO frequency can be easily controlled by e.g. changing the divider ratio N.
Highlights
Since their discovery in 2003,1 large expectations have arisen around a new type of nano-scale oscillator called spin-torque oscillator (STO)
We present a phase locked loops (PLL) system utilizing a vortex STO where major functions as RF amplifier, frequency divider, phase frequency detector and charge pump are implemented on custom integrated circuits
For a STO frequency of about 290 MHz and divider ratio of 16, the phase noise level is improved by 20 dB at an offset frequency of 100 kHz
Summary
Since their discovery in 2003,1 large expectations have arisen around a new type of nano-scale oscillator called spin-torque oscillator (STO). The spin transfer effect offers the possibility to nonlinearly convert a dc current into an rf voltage, or an rf current in a dc voltage These magnetic oscillators have key advantages, i.e. their ultra-small dimension, their low power consumption and their wide tuning range,[2,3] which make them promising candidates for the generation of microwave devices. The compatibility of its fabrication process to semiconductor manufacturing enables the efficient integration in integrated circuits applicable e.g. in future communication systems. Their small size and highly non-linear behavior come at the cost of degraded phase noise performance.
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