A Comparison of Frequency Pullability in Oscillators Using a Single AT-Cut Quartz Crystal and Those Using Two Single AT-Cut Crystals Connected in Parallel with a Series Load Capacitance or Series Load Inductance

This paper presents a comparison of frequency pullability in oscillators using a single AT-cut crystal and those using two single AT-cut crystals connected in parallel operated with a series load capacitance or series load inductance at fundamental frequencies of 4, 10 and 19 MHz. Pullability describes how the operating frequency may be changed by varying the load capacitance. The paper also gives impedance circuits for both single- and dual-crystal units. The experiment results show that the new approach using two single quartz crystals connected in parallel increases the frequency pulling range by 30-200% depending on the type of oscillator. Also given is the crystal frequency stability at these three frequencies.