Circuits and Methods of Synchronizing Differential Ring-Type Oscillators

A method of synchronizing a first differential ring-type oscillator and a second differential ring-type oscillator, each differential ring-type oscillator having differential output nodes, the method comprising:

• enabling the first differential ring-type oscillator to generate a first oscillating signal;
• enabling the second differential ring-type oscillator to generate a second oscillating signal;
• capacitively coupling, by at least one physical capacitor corresponding to each differential output node of each differential ring-type oscillator, the first and second differential ring-type oscillators;
• generating a first phase error signal according to a first signal associated with the first oscillating signal and a delayed version of a second signal associated with the second oscillating signal;
• generating a second phase error signal according to the second signal and a delayed version of the first signal;
• and
• generating one of a tuning signal and a pulse signal based on the difference between the first and second phase error signals.

A circuit comprising:

• a first oscillator having differential output nodes and configured to generate a first oscillating signal;
• a second oscillator having differential output nodes and configured to generate a second oscillating signal;
• a coupling structure capacitively coupling, by at least one physical capacitor corresponding to each differential output node of each differential ring-type oscillator, the first and second oscillators;
• a first phase comparator connected between the first and second oscillators and configured to generate a first phase error signal according to a first signal associated with the first oscillating signal and a delayed version of a second signal associated with the second oscillating signal;
• a second phase comparator connected between the first and second oscillators and configured to generate a second phase error signal according to the second signal and a delayed version of the first signal;
• and
• a control unit connected between the first and second phase comparators and configured to generate one of a tuning signal and a pulse signal based on the difference between the first and second phase error signals.