Digitally-tuned oscillator including a self-calibrating RC oscillator circuit
AssigneeAmerican Microsystems, Inc.
InventorTimothy G. O'Shaughnessy
Life of this patent
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Abstract
A digitally-tuned oscillator (DTO) includes a digital-to-analog converter (DAC) and an RC oscillator. The RC oscillator includes an RC circuit for forming a time constant equal to the RC product. However, this RC time constant is not used in the manner of a typical RC network to set the frequency of oscillation. Instead, the RC oscillator disclosed herein includes a separate oscillator, such as a voltage-controlled oscillator (VCO), and uses the RC time constant to compare with the oscillator-generated period and to adjust the frequency of the overall RC oscillator circuit in accordance with the comparison. The RC oscillator is self-calibrating.
Claims26
A digitally-tuned oscillator (DTO) comprising:
- a switched-capacitor digital to analog converter (DAC);
- and
- an RC oscillator coupled to the switched capacitor DAC.
A digitally-tuned oscillator (DTO) comprising:
- a switched-capacitor digital to analog converter (DAC);
- and
- an RC oscillator coupled to the switched capacitor DAC, the RC oscillator including:
- an RC network for setting an RC time constant;
- a core oscillator for generating a timing signal at a controlled frequency having an input terminal for controlling frequency of the core oscillator;
- a comparator coupled to the RC network and the core oscillator for comparing an indicator of the controlled frequency to an indicator of the RC time constant;
- and
- means responsive to the comparator for adjusting the frequency of the core oscillator.
A digitally-tuned oscillator (DTO) comprising:
- a switched-capacitor digital to analog converter (DAC);
- and
- an RC oscillator coupled to the Switched capacitor DAC, the RC oscillator including:
- a first input terminal coupled to an input resistance R;
- a second input terminal coupled to an input capacitance C;
- a ramp and hold circuit coupled to the first and second input terminals for establishing a time constant proportional to a multiplication product of the input resistance R and the input capacitance C;
- an oscillator generating an output timing signal having a period of oscillation established by a control input signal;
- a comparator coupled to the ramp and hold circuit and to the oscillator to compare an integer multiple of periods of the output timing signal to the time constant;
- and
- a control signal generator coupled to the oscillator and responsive to the comparator by generating an incremental signal to the control input signal to adjust the period of oscillation.
A digitally-tuned oscillator (DTO) comprising:
- a switched-capacitor digital to analog converter (DAC);
- and
- an RC oscillator coupled to the switched capacitor DAC, the RC oscillator
- including:
- a resistance R;
- a capacitance C;
- time constant means coupled to the resistance R and the capacitance C for establishing a time constant proportional to the multiplication product of the resistance R and the capacitance C;
- an oscillator means for generating a timing signal having a period of oscillation established by a control signal;
- a comparator means coupled to the time constant means and coupled to the oscillator means for comparing an integer multiple of periods of the timing signal to the time constant;
- and
- means coupled to the oscillator means and responsive to the comparator means for generating a control signal to adjust the period of oscillation of the timing signal, the control signal being generated by incrementing a previous version of the control signal.
Dependencies are inferred from the claim text.