Frequency linearization and sensitivity equalization of a frequency modulated crystal oscillator

Claim 1

In a frequency modulated crystal control oscillator including a current conducting device for providing amplification to sustain oscillations and a frequency determining circuit connected to said current conducting device for controlling the frequency of oscillation, said frequency determining circuit including a crystal element resonant at a frequency dependent upon a reactance connected in series therewith, the improvement for improving the linearity of the modulation of the oscillator, comprising: a voltage variable capacitance connected in series with said crystal element; a second capacitance coupled across the series combination of said crystal element and said voltage variable capacitance; a third capacitance connected across said voltage variable capacitance; said crystal element, said voltage variable capacitance, said second capacitance and said third capacitance forming a parallel resonant circuit at the fundamental frequency of said oscillator; means for applying an initial D.C. reference bias across said voltage variable capacitance to set the center frequency of oscillation; means for applying a modulating voltage across said voltage variable capacitance to change the capacitive reactance thereof to thereby change the frequency of operation of said crystal element and modulate the frequency of oscillations; and said second and third capacitances having selected capacitance values to provide a frequency deviation vs. voltage that is generally symmetrical about the initial D.C. reference bias.