Voltage-controlled oscillators using CFOAs with correction terminal Z

ABSTRACT

In this work, a realization of a voltage-controlled LC oscillator (VCO), using monolithic current-feedback operational amplifiers (CFOAs) with accessible correction terminal Z, is proposed. The frequency variation for the developed oscillator is obtained by replacing the capacitor in the resonant LC circuit with pairs of varactor diodes that use a common cathode. The barrier capacitance of the varactor diodes is controlled by a DC voltage obtained from an external voltage source. The proposed circuit configurations include single active element, a small number of discrete components, an operating frequency range of up to about 10 MHz and a relatively high value of the equivalent quality factor. To verify the effectiveness of the realised oscillators, results of computer simulations and experimental studies of sample electronic circuits using commercially available monolithic CFOAs with correction terminal Z are presented. Moreover, the obtained experimental results confirm the theoretical analyses of the circuits and the obtained mathematical expressions for the basic parameters, and the differences between them are within 10% and are mainly due to tolerances in the technological parameters of the used electronic components.

KEYWORDS:

• Analog circuits
• LC oscillators
• VCOs
• feedback
• CCII+
• CFOA

Acknowledgements

The author would like to thank G. Nikolov and B. Ganev of the “Automated systems for measurement and control” R&D laboratory for their help in the testing of the passive components for the various resonance circuits. Also, the author would like to thank the anonymous reviewers and associate editor for their helpful comments and suggestions that contributed to improving this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.