Features of multi-loop structures with OTAs and adjustable current amplifier for second-order multiphase/quadrature oscillators

This contribution presents two types of second-order multiphase oscillators based on the multiple-loop transfer modification. The main aim of this paper is to show the possibilities of two structures to generate multiphase outputs (phase shifts of multiples of π/2 and π/4) and the features resulting from this type of synthesis. We focused on independently and electronically adjustable oscillation condition for simple implementation of automatic amplitude gain control circuit (AGC) and linear electronic control of oscillation frequency. Basic two-loop structure (typical for band-pass response in multifunctional filtering structures) with additional loop of the feedback for control of oscillation condition was used. There are two different requirements for oscillation condition fulfillment in the same topology. These aspects (actual polarity of the loops transfers) are important for design of the AGC in specific case. Mutual relations between generated signals at available outputs of the circuits are studied. Design is supported by the detailed signal-flow graphs. Final circuits were verified by PSpice simulations.