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US 10,826,501 B1Granted
Ring oscillator based RC calibration circuit
AssigneeSilicon Laboratories Inc.
InventorsAbdulkerim L. Coban, Wenhuan Yu, Mustafa H. Koroglu
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Abstract
A calibration operation adjusts a frequency of a ring oscillator to a desired frequency by adjusting programmable RC circuits in the stages of the ring oscillator. The programmable RC circuits have programmable capacitors, resistors, or both. The RC circuits account for most of the delay through the ring oscillator. Another circuit with its own RC time constant is calibrated based on the adjustments made to the RC circuits in the ring oscillator to achieve the desired frequency.
Claims20
A method of performing a calibration operation comprising:
- operating a ring oscillator with RC time constants in respective stages of the ring oscillator and generating an oscillator output signal, the RC time constants being adjustable;
- dividing the oscillator output signal to generate a divided oscillator signal;
- asserting a load signal responsive to assertion of an enable signal and a transition of the divided oscillator signal, the enable signal allowing the ring oscillator to oscillate;
- loading a starting count value corresponding to a desired frequency into a counter responsive to the load signal;
- counting down the starting count value during a period of the divided oscillator signal to determine if the ring oscillator is oscillating above or below the desired frequency;
- if a count value of the counter goes to zero before an end of the period of the divided oscillator signal as indicated by a first value of a carry-out bit of the counter, thereby indicating an oscillation frequency of the ring oscillator is above the desired frequency, increasing the RC time constants to decrease the oscillation frequency of the ring oscillator, wherein after reaching zero the count value staying at zero during the period of the divided oscillator signal;
- if the count value is non-zero at the end of the period of the divided oscillator signal as indicated by a second value of a carry-out bit of the counter, thereby indicating the oscillation frequency is below the desired frequency, decreasing the RC time constants to increase the oscillation frequency of the ring oscillator;
- adjusting the RC time constants until the oscillation frequency of the ring oscillator is at the desired frequency, the RC time constants having a final value when the oscillation frequency is at the desired frequency;
- and
- adjusting another RC time constant in another circuit based on the final value of the RC time constants.
7 more elements
An integrated circuit comprising:
- a ring oscillator including an odd number of inverter stages, each inverter stage including,
- an inverter;
- and
- an RC circuit having an RC time constant that is adjustable;
- a divider to divide an output signal of the ring oscillator and provide a divided ring oscillator signal;
- a counter to load an initial count value corresponding to a desired oscillation frequency and to count down the initial count value for a period of the divided ring oscillator signal;
- wherein if a count value of the counter goes to zero before an end of the period of the divided ring oscillator signal, thereby indicating an oscillation frequency of the ring oscillator is above the desired oscillation frequency, the RC time constant of each inverter stage is increased to decrease the oscillation frequency of the ring oscillator, and wherein after reaching zero, the count value stays at zero during the period of the divided ring oscillator signal;
- wherein if the count value is non-zero at the end of the period of the divided ring oscillator signal, thereby indicating the oscillation frequency is below the desired oscillation frequency, the RC time constant of each inverter stage is decreased to increase the oscillation frequency of the ring oscillator;
- wherein the RC time constant of each inverter stage is adjusted until an oscillation frequency of the ring oscillator is at a desired oscillation frequency;
- and
- a second circuit independent of the ring oscillator and having a variable circuit parameter calibrated based on adjustments made to the RC time constant of each inverter stage to achieve the desired oscillation frequency.
8 more elements
An integrated circuit comprising:
- a ring oscillator including a plurality of inverting stages having programmable capacitor circuits disposed in each of the inverting stages, the ring oscillator supplying an oscillator output signal;
- wherein the ring oscillator is coupled to an enable signal that allows the ring oscillator to oscillate responsive to the enable signal being asserted;
- a calibration controller to measure an oscillation frequency of the oscillator output signal and to adjust the programmable capacitor circuits until the oscillation frequency is at a desired oscillation frequency, the calibration controller supplying the enable signal, the calibration controller including,
- a divider to divide the oscillator output signal of the ring oscillator and provide a divided ring oscillator signal;
- a counter to load an initial count value corresponding to the desired oscillation frequency and to count down the initial count value for a period of the divided ring oscillator signal;
- wherein a load signal is asserted to load the initial count value into the counter responsive to the enable signal being asserted and a transition of the divided ring oscillator signal;
- a functional circuit independent of the ring oscillator and having a variable capacitor circuit;
- and
- wherein the variable capacitor circuit is calibrated based on adjustments made to the programmable capacitor circuits to achieve the desired oscillation frequency.
6 more elements
Dependencies are inferred from the claim text.