Very low frequency quadrature oscillator

Abstract

We propose a low-cost, practical, quadrature oscillator with a period, Tq, which may be very long (Tq⩾1 s). We illustrate this design with an oscillator that produces two quadrature sinusoidal waves with a 1 s period. This design can be modified to provide signals of any shape by adjusting the value of one or more resistors. This design uses digital integrated circuits (ICs) and analog multiplexers. Digital ICs and an analog multiplexer are used to generate a stair-step waveform approximation by switching between the four members of a set of constant voltages. The duration, Tc, of each constant voltage is held constant (Tc=Tq/16). Then, a set of linear ramps, each ramp with a period Tc, is generated and selectively added to the stair-step approximation with another analog multiplexer. The use of multiplexed linear ramps, together with the stair-step approximation to the desired waveform, results in a smooth analog wave. The period, Tc=Tq/16, of the necessary linear ramp can be reduced as needed by increasing the number, 16, of stair-step per period, Tq, of the desired overall waveform. In this way, the values and sizes of components needed to generate high-quality waves with extremely long periods are made small enough to be practical. Experimental results of a detailed study of waveform quality are included.