Wide deviation voltage controlled crystal oscillator with temperature compensation

Claim 2

A wide deviation voltage controlled crystal oscillator, comprising: a. an amplifier; b. a source of tuning voltage c. and a voltage tunable crystal filter circuit coupled to the amplifier and the voltage source to to effect oscillations of the oscillator over a range of frequencies about a predetermined center frequency, said filter circuit including a first frequency compensating network to produce a substantially linear change of frequency versus voltage characteristic with a change in ambient temperature and a second frequency compensating network to correct the linear change in frequency versus voltage characteristic and thereby provide a substantially constant frequency versus voltage characteristic independent of ambient temperature change.

Claim 3

A wide deviation voltage controlled crystal oscillator substantially as described in claim 1, wherein the voltage tunable crystal circuit further includes: a. a piezoelectric crystal; b. a pair of parallel LC circuits connected in parallel with the piezoelectric crystal, each of said parallel LC circuits having a variable capacitor and an inductor; c. and a pair of series connected voltage variable capacitors connected in parallel with the parallel LC circuits, said tuning voltage applied at the junction between said voltage variable capacitors to vary the oscillator frequency.

Claim 4

A wide deviation voltage controlled crystal oscillator substantially as described in claim 2, wherein: a. the first frequency compensating neTwork includes a pair of parallel connected coupling capacitors coupled between a common junction of the pair of parallel LC circuits, the combined capacitance of said capacitors having a slightly negative temperature coefficient to compensate for the positive temperature coefficients of the other elements of the filter circuit, whereby the effect of temperature becomes a substantially identical shift of all tuning frequencies in a linear manner; b. and wherein the second frequency compensating network includes means for producing a linear temperature dependent compensating voltage providing a correcting biasing potential to the pair of voltage variable capacitors.

Claim 5

A wide deviation voltage controlled crystal oscillator substantially as described in claim 3, wherein the compensating voltage producing means comprises: a. a stable source of reference bias potential; b. a plurality of forward biased semiconductor diodes connected in series with the stable reference potential, said diodes exhibiting a negative temperature coefficient of contact potential; c. and a variable resistor connected in series with the semiconductor diodes, the voltage drop across said variable resistor providing the biasing potential for the voltage variable capacitors through the movable arm thereof.

Claim 6

A wide deviation voltage controlled crystal oscillator substantially as described in claim 4, wherein: a. the elements of the crystal filter circuit except the source of reference potential and the variable resistor are enclosed in a temperature-controlled chamber whose mean temperature is at the temperature turnover point of the piezoelectric crystal; b. and wherein the pair of coupling capacitors comprise a negative temperature coefficient capacitor and a highly stable positive or near zero temperature coefficient capacitor each contributing fractionally the total capacitance needed for the proper coupling of the pair of LC circuits.

Claim 7

A wide deviation voltage controlled crystal oscillator substantially as described in claim 5, wherein: a. the inductors of said LC circuits are wound on quartz formers with prestressed wire so that their temperature coefficients are substantially negligible; b. and the positive or near zero temperature coefficient capacitor of the pair of coupling capacitors is constructed from twined quartz.

Claim 8

In a voltage controlled crystal oscillator comprising an amplifier, a source of tuning voltage and a voltage tunable crystal filter circuit, wherein the oscillator is enclosed in a temperature-controlled chamber whose temperature is maintained near the temperature turnover point of the crystal, the improvement wherein said filter circuit comprises: a. a pair of capacitance coupled parallel LC circuits connected in a parallel configuration with said crystal; b. a pair of voltage variable capacitors for receiving the tuning voltage to produce oscillations over a range of frequencies about a predetermined center frequency; c. a pair of parallel connected coupling capacitors coupling said LC circuits, one of said capacitors having a negative temperature coefficient and the other of said capacitors having a positive of near zero temperature coefficient, the combined capacitance of said capacitors having a slightly negative temperature coefficient whereby the frequency shift caused by a change in temperature of said chamber is linear; d. and compensating means for correcting the linear change in frequency to produce a constant frequency for each tuned frequency, said compensating means comprising a voltage regulator, a plurality of forward biased semiconductor diodes connected serially with the voltage regulator and a variable resistor connected serially with the diodes, the voltage drop across said variable resistor providing a temperature dependent biasing potential for the voltage variable capacitors.

Claim 9

In a voltage controlled crystal oscillator comprising an amplifier, a source of tuning voltage and a voltage tunable crystal filter circuit, wherein the oscillator is enclosed in a temperature-controlled chamber whose temperature is maintained near the temperature turnover point of the crystal, the improvement wherein said filter circuit comprises: a. a pair of capacitance coupled parallel LC circuits connected in a parallel configuration with said crystal; b. a pair of voltage variable capacitors for receiving the tuning voltage to produce oscillations over a range of frequencies about a predetermined center frequency; c. a pair of parallel connected coupling capacitors coupling said LC circuits, one of said capacitors having a negative temperature coefficient and the other of said capacitors having a positive of near zero temperature coefficient, the combined capacitance of said capacitors having a slightly negative temperature coefficient whereby the frequency shift caused by a change in temperature of said chamber is linear; d. and compensating means for correcting the linear change in frequency to produce a constant frequency for each tuned frequency, said compensating means comprising a voltage regulator, a plurality of forward biased semiconductor diodes connected serially with the voltage regulator and a variable resistor connected serially with the diodes, the voltage drop across said variable resistor providing a temperature dependent biasing potential for the voltage variable capacitors.

Claim 10

In a voltage controlled crystal oscillator substantially as described iN claim 7, wherein: a. each of the parallel LC circuits have a variable capacitor and an inductor connected in a parallel configuration; b. and wherein said positive or near zero temperature coefficient capacitor is substantially stable and contributes fractionally to the total capacitance needed for the proper coupling of said LC circuits.