Methods and apparatus for calibration and temperature compensation of oscillators having mechanical resonators
Methods and apparatus for calibration and temperature compensation of oscillators having mechanical resonators are described. The method(s) may involve measuring the frequency of the oscillator at multiple discrete temperatures and adjusting compensation circuitry of the oscillator at the various temperatures. The compensation circuitry may include multiple programmable elements which may independently adjust the frequency behavior of the oscillator at a respective temperature. Thus, adjustment of the frequency behavior of the oscillator at one temperature may not alter the frequency behavior at a second temperature.
1. A method of calibrating temperature compensation circuitry of an oscillator, the oscillator comprising a mechanical resonator coupled to the temperature compensation circuitry, the method comprising:
setting a first temperature of the oscillator;
adjusting a first component of the temperature compensation circuitry to set an output frequency of the oscillator to a desired value at the first temperature;
setting a second temperature of the oscillator; and
adjusting a second component of the temperature compensation circuitry to set the output frequency of the oscillator to the desired value at the second temperature,
wherein the first component and the second component are digital-to-analog converters (DACs), and wherein adjusting those components comprises programming values into those components, and
wherein the DACs are not linear DACS.
2. The method of claim 1 , wherein the method of calibrating the temperature compensation circuitry does not involve performing a temperature sweep with the oscillator.
3. The method of claim 1 , wherein the first and second temperatures are stable but not accurate.
4. A method of calibrating temperature compensation circuitry of an oscillator, the oscillator comprising a mechanical resonator coupled to the temperature compensation circuitry, the method comprising:
setting a first temperature of the oscillator;
adjusting a first component of the temperature compensation circuitry to set an output frequency of the oscillator to a desired value at the first temperature;
setting a second temperature of the oscillator; and
adjusting a second component of the temperature compensation circuitry to set the output frequency of the oscillator to the desired value at the second temperature,
further comprising setting a third temperature of the oscillator and adjusting a third component of the temperature compensation circuitry to set the output frequency of the oscillator to the desired value at the third temperature, wherein each of the first, second, and third components is a digital-to-analog converter (DAC) configured to independently adjust the output frequency of the oscillator independent of the other two of the DACs.
5. A temperature compensation circuit configured to form part of an oscillator comprising a mechanical resonator, the temperature compensation circuit comprising:
at least first and second adjustable circuit components configured to independently alter an output frequency of the oscillator,
wherein the at least first and second adjustable circuit components comprise a first adjustable circuit component, a second adjustable circuit component, and a third adjustable circuit component, and
wherein the first adjustable circuit component is configured to control a linear component of a temperature-dependent frequency response of the oscillator,
wherein the second adjustable circuit component is configured to control a quadratic component of the temperature-dependent frequency response of the oscillator, and wherein the third adjustable circuit component is configured to control a cubic component of the temperature-dependent frequency response of the oscillator,
further comprising a plurality of adders coupled to the first, second, and third adjustable circuit components,
wherein each of the first, second, and third adjustable circuit components is a digital-to-analog converter (DAC), and wherein the temperature compensation circuit further comprises a fourth DAC coupled to at least one first adder of the plurality of adders and a fifth DAC coupled to at least one second adder of the plurality of adders.
6. The temperature compensation circuit of claim 5 , wherein one adder of the plurality of adders receives an input from a temperature sensor.