The Implementation of Single VCII-Based RC Sinusoidal Oscillators: 28 Novel Configurations
Sinusoidal oscillators are key components in electronics, widely used in applications like telecommunications, instrumentation, and biomedical, etc. Their design is complex, requiring careful consideration of energy efficiency, distortion, frequency, stability, accuracy, and sensitivity to parasitic elements and component tolerances. These complexities make oscillator design a long-standing and active research area.
Oscillators are commonly categorized by their passive components: RC (Resistor-Capacitor) for low-frequency systems and LC (Inductor-Capacitor) for high-frequency applications where low signal power loss is critical. RC oscillators traditionally use operational amplifiers (OA) for their availability and ease of integration. Current-mode processing, however, offers better bandwidth and dynamic range, especially at low supply voltages, though its current output is less convenient for readout than voltage. The introduction of the Second-Generation Voltage Conveyor (VCII) combines the advantages of current-mode operation with a practical voltage output, making it increasingly popular in analogue signal processing.
This study presents 28 RC oscillator schemes, all featuring a compact design requiring only one VCII, three resistors, and two capacitors. This minimalist design outperforms OA-based circuits, which usually need at least four resistors and two capacitors. The reduced component count lowers power dissipation, while the VCII’s internal biasing ensures inherent energy efficiency. Its low-impedance Z port eliminates the need for a voltage buffer, minimizing quiescent current and total power consumption—overcoming a key limitation that previously restricted current-mode circuit adoption.
The ideal VCII acts as a voltage buffer from X to Z and a current buffer from Y to X, with zero impedance at Y and Z and infinite impedance at X. In practice, non-idealities like finite impedances and non-unitary gains arise, modelled by parasitic resistances, inductances, and capacitances at the terminals.
The paper presents a comprehensive theoretical framework for deriving the oscillation conditions (OC) and oscillation frequencies for all 28 circuits. The circuits are grouped into seven categories, each characterized by different sets of admittance-based characteristic equations. Each group has its own design rules and frequency formulas, enabling designers to tailor circuits to specific requirements. Sample designs and frequency equations are provided for each group.
To validate the theory, the proposed circuits were implemented using the AD844 IC, configured to emulate a VCII− with two VCII+ blocks. Of the 28 circuits, 16 were experimentally validated, producing oscillations as predicted. The remaining 12 failed due to parasitic effects of the AD844, such as inductive and capacitive artifacts. However, simulations with an ideal VCII confirmed their theoretical correctness, suggesting these designs may still function with alternative or custom VCII implementations.
The study also highlights the potential of these circuits in sensor interface applications, particularly where environmental parameters affect circuit components like resistors or capacitors. As a use case, the paper demonstrates an oscillator configuration using three identical thermistors, showing that environmental temperature changes directly affect the oscillation frequency, with a relative error below 8%.
The detailed theoretical analysis, coupled with experimental validation, provides a valuable resource for researchers and designers seeking compact, low-power solutions for various electronic applications, particularly in sensor interfacing.