Low-Distortion Wideband Tunable Sinusoidal Oscillator Based on Multiple Feedback Band-Pass Filter for Impedance Measurements

Sinusoidal oscillators, as excitation sources for impedance measurements, require high signal quality for accurate measurements. However, traditional amplitude control methods, such as automatic gain control (AGC) or Zener clipping amplitude control, introduce either system complexity or additional total harmonic distortion (THD). In this paper, a sinusoidal oscillator topology based on multiple feedback band-pass filter is proposed, which employs antiparallel diode pairs that exploit diodes’ forward characteristics to efficiently generate low-THD, amplitude-tunable sinusoidal signals at low amplitudes. The proposed topology is capable of generating low-distortion sinusoidal signals with specified amplitudes across a frequency range of 10Hz to 1MHz. Within the range of 1kHz to 1MHz, the THD is less than 0.0900%, and below 1kHz, the THD is less than 0.1694%. Methods for generating low-distortion sinusoidal signals are also analyzed. In complex impedance demodulation applications, compared to DDS solution, the improved demodulation accuracy of the proposed topology highlights the indispensable role of high-precision single-frequency excitation sources.