RC oscillator admits negative frequency

• Published in: International journal of circuit theory and applications Vol. 39; no. 6; pp. 687 - 695
• Main Author: Williamsen, Mark S.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.06.2011
• Subjects: Amplitudes; analog multipliers; audio oscillators; Circuits; closed-loop systems; Computer simulation; Discontinuity; Frequency ranges; log ratio amplifiers; Mathematical models; Oscillators; quadrature oscillators; RC oscillators; Reinforced concrete; state variable oscillators; two integrator oscillators
• ISSN: 0098-9886; 1097-007X; 1097-007X
• DOI: 10.1002/cta.640

The humble resistance–capacitance (RC) oscillator has held our attention for nearly seven decades. During that time many improvements have been made to enhance the performance and the range of applicability. In this letter we consider further refinements that extend the frequency range to include zero, and even negative frequencies. This allows the frequency to be swept through zero with no discontinuity in phase or amplitude. We then suggest an addition to the well‐known automatic level control (ALC) circuits to linearize the control function, with attendant benefits in modeling, simulation, and implementation. Closed‐loop dynamics for the improved ALC circuit are predicted, then verified by experiment. Copyright © 2010 John Wiley & Sons, Ltd. A state variable oscillator has been develope dwith symmetric independent damping and frequency terms, allowing positive or negative rotation in the complex plane. A log ratio amplifier replaces the traditional differential error amplifier, linearizing the amplitude control loop. We describe for the first time an RC oscillator in which large‐scale amplitude changes can be accurately modeled with a simple transfer function, independent of oscillation frequency. Copyright © 2010 John Wiley & Sons, Ltd.