Active and Passive Electronic Components 
Volume 2008 (2008), Article ID 539618, 6 pages
doi:10.1155/2008/539618
Research Article

Amplitude and Frequency Control: Stability of Limit Cycles in Phase-Shift and Twin-T Oscillators

J. P. Dada,1 J. C. Chedjou,2 and S. Domngang1

 1Department of Physics, Faculty of Science, University of Yaoundé-I, P.O. Box 812, Yaoundé, Cameroon
2Department of Physics, Faculty of Science, University of Dschang, P.O. Box 67, Dschang, Cameroon
Received 1 October 2007; Revised 25 March 2008; Accepted 29 April 2008

Recommended by Fahrettin Yakuphanoglu

Abstract

We show a technique for external direct current (DC) control of the amplitudes of limit cycles both in the Phase-shift and Twin-T oscillators. We have found that amplitudes of the oscillator output voltage depend on the DC control voltage. By varying the total impedance of each oscillator oscillatory network, frequencies of oscillations are controlled using potentiometers. The main advantage of the proposed circuits is that both the amplitude and frequency of the waveforms generated can be independently controlled. Analytical, numerical, and experimental methods are used to determine the boundaries of the states of the oscillators. Equilibrium points, stable limit cycles, and divergent states are found. Analytical results are compared with the numerical and experimental solutions, and a good agreement is obtained.