Narrow deviation voltage controlled crystal oscillator for mobile radio
OwnerMichael M. Driscoll, Rafi Arakelianinventors
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Abstract
A linear sensitivity voltage controlled crystal oscillator of the type including a resonator coupled to a negative resistance generator. The resonator comprises a crystal connected in series with a voltage variable capacitance device. The response of the resonator is linearized by the addition of an inductance across the voltage variable capacitance device. A resistor is shunted across the crystal to prevent oscillation at spurious resonances of the resonator.
Claims15
In a voltage controlled crystal oscillator (VCXO) for providing an output signal of a frequency in accordance with a control voltage applied thereto, said VCXO being of the type including a composite resonator coupled to a negative resistance generator, said composite resonator comprising a crystal, in series connection with a parallel combination of a voltage variable capacitance device, responsive to a control voltage applied thereto, and an inductance;
- said crystal having a unit static capacitance associated therewith and said voltage variable capacitance having a predetermined reactance versus voltage characteristic, the improvement wherein:
- said inductance is of a predetermined value equal to the parallel combination of (a) a first inductance exhibiting a reactance complementary to the reactance of said unit static capacitance and (b) a second inductance exhibiting a reactance to provide, when in effective parallel connection across said voltage variable capacitance, an inflection point in the reactance versus voltage characteristic of the parallel combination of said second inductance and said voltage variable capacitance at a nominal mid-band value of said control voltage.
In a voltage controlled crystal oscillator (VCXO) of the type including a resonator coupled to a negative resistance generator, said resonator comprising a crystal, a voltage variable capacitance device, a linearization inductance, the improvement wherein:
- said variable capacitance device is coupled in series with said crystal and said inductance is effectively an inductor coupled across said variable capacitance device;
- said crystal having a motional inductance of L.sub.1, motional capacitance of value C.sub.1, static capacitance of value C.sub.0 and series resonant frequency .omega..sub.s, said voltage variable capacitance being an abrupt junction varactor with a contact potential .phi. and four volt capacitance C.sub.-4, and said inductor has a value of L.sub.L where:
- L.sub.L = [(1/.omega..sub.s.sup.2 C.sub.0) (3/.omega..sup.2 C.sub.-4) ((V.sub.0 + .phi.)/(4 + .phi.)).sup.1/2 ]/[(1/.omega..sub.s.sup.2 C.sub.0) + (3/.omega..sup.2 C.sub.-4) ((V.sub.0 + .phi.)/(4 + .phi.)).sup.1/2 ] and C.sub.-4 = (-9/16K.sub.0) (1/.omega..sub.s L.sub.1) ((V.sub.0 + .phi.) (4 + .phi.)).sup.-1/2
- wherein K.sub.0 is the sensitivity of said VCXO and V.sub.0 is a bias voltage applied to said varactor and .omega. is the nominal frequency of operation of said VCXO.
A voltage controlled crystal oscillator (VCXO) comprising:
- a resonator including a crystal coupled to a voltage variable capacitance device, and a linearization inductance, said resonator having an effective series resistance;
- p1 a negative resistance generator, responsive to signals from said resonator, for sustaining oscillation when the magnitude of said negative resistance is greater than the effective series resistance of said resonator;
- and means, cooperating with said resonator, for selectively increasing said effective series resistance to a value greater than said negative resistance magnitude at frequencies outside of a predetermined range of frequencies, to prevent thereby oscillation at spurious resonant frequencies of said resonator.
Dependencies are inferred from the claim text.