Variable frequency crystal oscillator using variable negative inductance or capacitance

This letter refers to one by Capparelli and Verrazzani [1]. Its aim is to present new techniques for building a variable frequency crystal oscillator based on the use of a negative inductor or capacitor. The interval available for the frequency deviation is larger than the one existing between the natural frequencies f
p
and f
s
of the crystal. The spurious frequencies uncontrolled by the crystal are absent.