OTA-C Arbitrary-Phase-Shift Oscillators

This paper exhibits the generation of an operational transconductance amplifier and capacitor (OTA-C) arbitrary-phase-shift sinusoidal oscillator (APSO) for an order n >= 3 for various advanced applications. A new nth-order quadrature oscillator (QO) is obtained via the algebraic quadrature manipulations of an oscillatory characteristic equation. Based on a phase shift transformation from a quadrature, an APSO is then generated by superposing OTAs with required +/- transconductance(s) in parallel with some grounded capacitor(s) on the QO. For eliminating nonideal and parasitic effects to improve phase accuracy, phase compensation schemes are proposed. A new native amplitude control exploiting the nonlinearity of all employed OTAs of the APSO is presented as well to lead to rather low THD and a lower variation of THD with respect to amplitude enlargement. A fourth-order APSO is demonstrated and simulated using Hspice with a 0.35-mu m process for validation. In addition, its real application to a polyphase rectifier is improved. Finally, an experiment using LM13700s shows favorable potential of APSOs.