On 'Discussion on Barkhausen and Nyquist stability criteria'

摘要

The present article is related to the recently published paper given in Singh (Analog Integr Circuits Signal Process, 62, 327-332, 2010), which depicts the failure of Barkhausen criterion concerning the determination of condition of oscillation for startup of sinusoidal oscillation. In particular, the sinusoidal oscillator circuit considered in this article is one of the possible four alternatives of the Wien-bridge oscillator (WBO). In other previous articles by the same aforementioned author (Singh, Analog Integr Circuits Signal Process 48, 251-255, 2006; Singh, Analog Integr Circuits Signal Process 50, 127-132, 2007), some examples are provided with the objective of sustaining this hypothesis. In this article, however, the study of RC oscillator circuits based on the Barkhausen criterion is reconsidered. This point of view involves to consider the classical structure of a sinusoidal oscillator as a system consisting of a positive feedback loop composed of a general amplifier block (with its corresponding local negative feedback that stabilizes the gain) plus a general passive network. Taking into account this point of view, it is shown that Barkhausen criterion (specifically, the practical form of this criterion) allows to predict properly the startup of oscillations of the circuit considered in the article (Singh 2010).