Novel technique for dual-mode quartz oscillators

This paper describes a novel concept in the design of dual-mode quartz crystal oscillators that are widely used in sources with improved frequency stability. The suggested scheme incorporates a single feedback loop comprising a sustaining amplifier with a triangular amplitude characteristic loaded on a pass filter with two low-Q resonant frequencies followed by a quartz network. The feedback is positive for one mode and negative for another. As a result, the oscillator is capable of providing essentially different harmonics as two simultaneous oscillations can occur only when the magnitude of the chosen “positive” mode becomes high enough