RC oscillator admits negative frequency

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 (C) 2010 John Wiley & Sons, Ltd.