A recently published paper (Singh, Analog Integr Circuit Signal Process, 62:327–332, 2010) dealing with the relationship between the Barkhausen condition for oscillation and the well known Nyquist stability criterion for systems with feedback is highly appreciated. However, it seems to be necessary to place some comments on it. The circuit examples presented in the cited paper as well as the conclusions will be critically reviewed. Apparently, there is still no sufficient oscillation condition. Therefore, the necessity to complete the existing oscillation criterion with a sufficient condition is emphasized.
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