Downshift Techniques for Oscillator with Feedback Loop

An apparatus, comprising:

• an oscillator configured to generate an output clock signal based on one or more control signals;
• feedback circuitry configured to control the oscillator based on the output clock signal;
• and
• first circuitry configured to operate based on the output clock signal when the apparatus is in both:
• a closed-loop mode in which the feedback circuitry is configured to vary at least one of the one or more control signals based on both the output of the oscillator and a reference signal to cause the oscillator to generate the output clock signal at a first frequency;
• and
• an open-loop mode in which the oscillator generates the output clock signal at a second frequency, without feedback based on output of the oscillator;
• sensor circuitry configured to output a trigger signal in response to detecting a first state of the first circuitry during operation of the apparatus;
• and
• control circuitry configured to transition the apparatus from the closed-loop mode to the open-loop mode in response to the trigger signal.

A method, comprising:

• generating, by an oscillator, an output clock signal based on one or more control signals;
• controlling the oscillator, by feedback circuitry, based on the output clock signal;
• and
• operating first circuitry in a closed-loop mode in which the feedback circuitry varies at least one of the one or more control signals based on both the output of the oscillator and a reference signal to cause the oscillator to generate the output clock signal at a first frequency;
• detecting, by sensor circuitry, a first state of the first circuitry during operation of the first circuitry;
• and
• transitioning to operating the first circuitry in an open-loop mode based on the detecting, oscillator generates the output clock signal at a second frequency, without feedback based on output of the oscillator, in the open-loop mode.

A non-transitory computer readable storage medium having stored thereon design information that specifies a circuit design in a format recognized by a fabrication system that includes a processor that is configured to process the design information, wherein the fabrication system is configured to fabricate, based on the processing, a hardware integrated circuit that includes circuitry configured to operate according to the circuit design, wherein the circuitry includes:

• an oscillator configured to generate an output clock signal based on one or more control signals;
• feedback circuitry configured to control the oscillator based on the output clock signal;
• and
• first circuitry configured to operate based on the output clock signal when the circuitry is in both:
• a closed-loop mode in which the feedback circuitry is configured to vary at least one of the one or more control signals based on both the output of the oscillator and a reference signal to cause the oscillator to generate the output clock signal at a first frequency;
• and
• an open-loop mode in which the oscillator generates the output clock signal at a second frequency, without feedback based on output of the oscillator;
• sensor circuitry configured to output a trigger signal in response to detecting a first state of the first circuitry during operation of the first circuitry;
• and
• control circuitry configured to transition the circuitry from the closed-loop mode to the open-loop mode in response to the trigger signal.