A Low-Frequency Sinusoidal Voltage Controlled Oscillator Based on Switched Capacitor Filters

Low-frequency sinusoidal Voltage Controlled Oscillators (VCO) are used as signal generation modules in instruments for Electrical Impedance Spectroscopy (EIS), which has several important applications in contexts such as biomedical and agricultural, for help in the diagnosis of human and plant diseases, respectively. Unfortunately, the design of sinusoidal VCO for low-frequencies has several issues, such as the difficulty of sweep-of-frequency, voltage-to-frequency nonlinearity, harmonic content, and difficulty of integration on a chip. To address this, we propose a low-frequency sinusoidal VCO that uses a square wave VCO to control the frequency of a switched capacitor based oscillator. As proof of concept, a circuit with two commercial Integrated Circuits is implemented in a breadboard and the results are analyzed in terms of Total Harmonic Distortion and input-output relationship for a frequency range from 1 Hz to 12 kHz.