Comparison between the Series and Parallel Power Output Summation Arrangements for an Ensemble of Self-oscillators

Abstract

The parallel and serial arrangements for summing the power outputs in large ensembles of sine-wave self-oscillators (SO) are investigated. The study was prompted by research activities carried out in the field of spintronics and spin-transfer nanooscillators (STNO). The main drawback of such oscillators is a low power level of the generated oscillations (a few hundred of nanowatts); therefore, one of possible ways for increasing the power output of STNO-based devices is combining them into ensembles to synchronize and sum up their power outputs. In summing up the powers of active elements, bridge circuits are used, which provide mutual decoupling and lack of connection through the common load. The use of bridge circuits for summing up the powers of nanoscale oscillators does not seem to be feasible because the number of generators can reach several hundred. In view of this circumstance, a need arises to seek for the best way of combining the generators (the uniting geometry) and the method for arranging their connection with the load. One possible way in which nanooscillators can be interlinked is to unite their current circuits by means of short-circuited connectors to form either a parallel or a series wiring schemes. Abridged equations of ensembles were derived proceeding from the simplified equivalent circuit of a single self-oscillator consisting of an oscillating loop with losses and a nonlinear active element, and the elementary equal-amplitude synchronous modes are investigated. The obtained models were used to construct a family of SO ensemble external load characteristics. In addition, the ensemble operation conditions are found for the case when an arbitrary number of ensemble elements fail in emergency manner. It is shown that if M elements in the ensemble consisting of N self-oscillators fail, their parallel-connected arrangement will remain operable only if N > 2M, whereas the series-connected scheme will remain operable with any N > M. It should be pointed out that the self-excitation condition for the parallel scheme is not fulfilled if M > N/2. If there occurs a short-circuit fault in the parallel scheme and an open-circuit fault in the series scheme, the entire ensemble fails. Therefore it is necessary to use more intricate component combining topologies, e.g., to unite the considered types of ensembles into sub-ensembles. The obtained results are of importance in constructing large ensembles of SOs (specifically, spin-transfer nanooscillators) when the implementation of bridge circuits is impossible.