A Spintronic Voltage-Controlled Stochastic Oscillator for Event-Driven Random Sampling

A voltage-controlled stochastic oscillator (VCSO) utilizing a magnetic tunnel junction (MTJ) is introduced. The VCSO can be used in analog-to-digital information conversion systems for low-energy applications. Experiments show that the thermally activated switching rate of the MTJ is modulated by using an applied voltage across the device via the voltage-controlled magnetic anisotropy effect. The MTJ is deliberately designed to have a relatively short retention time by reducing the perpendicular magnetic anisotropy. The macrospin MTJ compact model is implemented into a circuit design platform as a noise source, which allows the VCSO to generate an event-driven stochastic sampling signal (ESS). Since the average sampling frequency of the ESS is efficiently modulated by the maximum frequency of the input signal, it can drastically reduce the energy consumption of the system. The circuit simulation shows that the frequency range of the ESS and its slope can be optimized by adjusting the MTJ parameters. The VSCO can achieve 20 times improvement in area-efficiency and reduce power consumption by more than three times compared with the previous works.