Network for temperature compensation of an AT cut quartz crystal oscillator
AssigneeRCA Corporation
InventorBortolo M. Pradal
Life of this patent
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Abstract
A network for temperature compensation of a crystal oscillator over an extended temperature range encompassing two points of inflection of the drift characteristic of an AT cut crystal. The oscillator is of the type having, in loop connection, an AT cut quartz crystal and a voltage variable capacitance device. The compensation network utilizes a three resistor, three thermistor electrical network for generating a temperature dependent bias voltage applied to the variable capacitance device to compensate for changes in the self-resonant frequency of the crystal due to temperature variation. A method for determining the component values for the compensation network is also disclosed.
Claims9
In a crystal oscillator of the type including a resonant circuit and means for sustaining oscillations in said resonant circuit, said resonant circuit including in loop connection a voltage variable capacitance device and a crystal, said crystal having a temperature dependent self-resonant frequency, and a predetermined frequency drift characteristic, said oscillator further including means for generating a bias signal having an aplitude varying in accordance with temperature, said bias signal being applied to said voltage variable capacitance device to vary the capacitance of said device to compensate for temperature dependent changes in said crystal self-resonant frequency,
- said bias signal matching a predetermined theoretical compensation voltage versus temperature curve at a plurality of predetermined temperatures within a predetermined range of temperatures,
- said means for generating said bias signal comprising a temperature dependent potential dividing network means, responsive to a fixed bias potential applied across first and second terminals, for providing said bias signal between said second terminal and a third terminal, the improvement wherein:
- said crystal has a frequency drift characteristic approximately in accordance with an equation of the third degree in temperature change having upper and lower inflection points within said predetermined range of temperatures;
- and
- said temperature dependent potential dividing means comprises first, second, third, fourth, fifth and sixth resistances, said first, second and third resistances exhibiting substantially zero temperature coefficients and said fourth, fifth and sixth resistance exhibiting predetermined negative temperature coefficients;
- a parallel connection of said first and said fourth resistances;
- said parallel connection being serially coupled with said second resistance between said first and third terminals;
- said third and said fifth resistances being serially coupled between said second and third terminals;
- and
- said sixth resistance being coupled between said second and third terminals.
In a crystal oscillator of the type including a resonant circuit and means for sustaining oscillations in said resonant circuit, said resonant circuit including a loop connection a voltage variable capacitance device and a crystal, said crystal having a temperature dependent self-resonant frequency, and a predetermined frequency drift characteristic, said oscillator further including means for generating a bias signal having an amplitude varying in accordance with temperature, said bias signal being applied to said voltage variable capacitance device to vary the capacitance of said device to compensate for temperature dependent changes in said crystal self-resonant frequency,
- said bias signal matching a predetermined theoretical compensation voltage versus temperature curve at a plurality of predetermined temperatures, the improvement wherein:
- said crystal has a frequency drift characteristic approximately in accordance with an equation of the third degree in temperature change having upper and lower inflection points within a predetermined range of temperatures;
- and
- said plurality of predetermined temperatures include temperatures substantially equal to said inflection point temperatures, the upper and lower temperatures of said range of temperatures and a temperature approximately in the middle of said range of temperatures,
- said means for generating said bias signal comprising a temperature dependent potential dividing network means, responsive to a fixed bias potential applied across first and second terminals, for providing said bias signal between said second terminal and a third terminal,
- said temperature dependent potential dividing means comprises first, second, third, fourth, fifth and sixth resistances, said first, second and third resistances exhibiting substantially zero temperature coefficients and said fourth, fifth and sixth resistances exhibiting predetermined negative temperature coefficients;
- a parallel connection of said first and said fourth resistances;
- said parallel connection being serially coupled with said second resistance between said first and third terminals;
- said third and said fifth resistances being serially coupled between said second and third terminals, and
- said sixth resistance being coupled between said second and third terminals.
Dependencies are inferred from the claim text.