High accuracy rc oscillator

A device comprising:

• an RC oscillator circuit operable to provide a tunable output frequency, the oscillator circuit including a bias circuit switchable between first and second modes of operation, one of which has less drift in oscillator bias current relative to the other mode;
• drift compensation circuitry operable to compensate for drift in the oscillator output frequency in a closed-loop mode of operation based on a comparison of the oscillator output frequency with a reference frequency;
• and
• a processor operable to compensate for temperature-based drift in the oscillator frequency in an open-loop mode of operation based on a measured temperature value in a vicinity of the oscillator circuit,
• wherein the RC oscillator circuit comprises a tunable capacitor and a tunable resistor, each of which is adjusted according to a respective input value, wherein during operation according to the closed-loop and open-loop modes, the input value for the tunable resistor is adjusted, respectively, by the drift compensation circuitry and by the processor.

A method of operating an RC oscillator circuit that provides a tunable output frequency, the method comprising:

• providing a signal to the oscillator circuit to cause a bias circuit for the oscillator circuit to switch between first and second modes of operation, one of which has less drift in oscillator bias current relative to the other mode, wherein the bias circuit includes a proportional-to-absolute-temperature branch and a complementary-to-absolute-temperature branch, the method including:
• enabling only the proportional-to-absolute-temperature branch in the first mode of operation, and
• enabling both the proportional-to-absolute-temperature branch and the complementary-to-absolute-temperature branch in the second mode of operation, the method further including:
• generating a mode selection signal to enable one of the following modes of operation:
• a closed-loop mode of operation based to compensate for drift in the oscillator output frequency based on a comparison of the oscillator output frequency with a reference frequency or an open-loop mode of operation to compensate for temperature-based drift in the oscillator frequency based on a measured temperature value in a vicinity of the oscillator circuit.

An RC oscillator circuit operable to provide a tunable output frequency, the oscillator circuit comprising:

• a tunable capacitor, and a resistor that is tunable independently of the capacitor;
• and
• a bias circuit switchable between first and second modes of operation, one of which has less drift in oscillator bias current relative to the other mode,
• wherein the bias circuit includes a proportional-to-absolute-temperature branch and a complementary-to-absolute-temperature branch, wherein in the first mode of operation, only the proportional-to-absolute-temperature branch is enabled, and wherein in the second mode of operation, both the proportional-to-absolute-temperature branch and the complementary-to-absolute-temperature branch are enabled.

A method of operating an RC oscillator circuit that provides a tunable output frequency, the method comprising:

• comparing an output frequency of the oscillator circuit with a reference frequency;
• adjusting an input value for a tunable resistor in the oscillator circuit based on the comparison;
• detecting that the input value for the tunable resistor corresponds to a highest or lowest value within a specified range of possible values;
• and
• generating an error signal if the highest or lowest value is detected.