Current Oscillator Based on Pyragas Model for Electrical Bioimpedance Applications

Abstract

Current sources play an essential role in tissue excitation used in bioelectrical impedance spectroscopy. Most investigations use Howland current sources that, despite their practicality and simplified implementation, have operating frequency limitations and dependence on the load impedance due to their narrow output impedance, especially at higher frequencies. The objective of this work is to propose a model for a robust current-controlled sinusoidal oscillator. The oscillator is based on fully analog electronics, which enables controlling the oscillation phase and amplitude by using a voltage reference. The mathematical model is based on Pyragas control application to the classical harmonic oscillator. From the modeling process, an oscillator topology was built based on second-generation current carriers and on transconductance amplifiers. A sinusoidal voltage source having a frequency of 1 MHz and an amplitude of 1Vpp was used as a reference signal to drive the oscillator. The oscillator output current synchronized the oscillations’ phase and amplitude using the reference, regardless of their magnitude before the control signal acted in the circuit at t≈13.5μs. SPICE simulations using ideal components have confirmed the successful operation of the proposed oscillator. This type of oscillator can be implemented in SOIC, then allowing oscillation control interface with logic circuits.