  Magnetic tunnel junction (MTJ) spin torque oscillators (STO) have shown the
potential to be used in a wide range of microwave and sensing applications. To
evaluate potential uses of MTJ STO technology in various applications, an
analytical model that can capture MTJ STO's characteristics, while enabling
system- and circuit-level designs, is of great importance. An analytical model
based on macrospin approximation is necessary for these designs since it allows
implementation in hardware description languages. This paper presents a new
macrospin-based, comprehensive and compact MTJ STO model, which can be used for
various MTJ STOs to estimate the performance of MTJ STOs together with their
application-specific integrated circuits. To adequately present the complete
model, this paper is divided into two parts. In Part I, the analytical model is
introduced and verified by comparing it against measured data of three
different MTJ STOs, varying the angle and magnitude of the magnetic field, as
well as the DC biasing current. The proposed analytical model is suitable for
being implemented in Verilog-A and used for efficient simulations at device-,
circuit- and system-levels. In Part II, the full Verilog-A implementation of
the analytical model with accurate phase noise generation is presented and
verified by simulations.
