Oracle International Corporation

Eric Y Chang

Frankie Liu

Philip Amberg

Suwen Yang

Guanghua Shu

Ziad Saleh Shehadeh

Ashok V Krishnamoorthy

Xuezhe Zheng

Ronald Ho

Elad Alon

We disclose a system, which performs a duty-cycle correction operation for an injection-locked phase-locked loop (PLL). The system first obtains a pattern of positive and negative error pulses at rising and falling edges of a reference clock signal for the injection-locked PLL, wherein the pattern specifies deviations of the reference clock signal from a 50% duty cycle. The system multiplies the pattern of positive and negative error pulses by a duty-cycle distortion (DCD) template, which specifies a sign of a duty-cycle error for the reference clock signal, to calculate duty-cycle distortion values. The system then accumulates the duty-cycle distortion values to produce a duty-cycle-error amplitude. Next, the system multiplies the duty-cycle-error amplitude by the DCD template to produce a duty-cycle correction signal. Finally, the system uses the duty-cycle correction signal to compensate for timing errors in the injection-locked PLL, which are caused by duty-cycle variations in the reference clock signal.

Digitally assisted feedback loop for duty-cycle correction in an injection-locked PLL

In an optical device, a ring-resonator modulator, having an adjustable resonance (center) wavelength, receives an optical signal that includes a carrier wavelength from an input-output optical waveguide. Then, a monitoring mechanism monitors a performance metric (such as an average power or a signal swing) of a monitor optical signal from the ring-resonator modulator. Moreover, control logic in the optical device adjusts the resonance wavelength based on the monitored performance metric so that the resonance wavelength is locked to the carrier wavelength. In particular, the control logic may apply a change to an adjustment signal that is provided to the ring-resonator modulator. If the change increases the performance metric, the control logic may continue to modify the resonance wavelength. Otherwise, the control logic may modify the resonance wavelength by applying one or more changes, having an opposite sign to the change, to the adjustment signal.

In-situ ring-resonator-modulator calibration

During operation, the system uses a differential ring oscillator to generate the output clock signal. Next, the system uses a phase detector to detect errors comprising deviations between edges of the output clock signal and a reference clock signal. The system subsequently uses a frequency-tracking path to adjust a frequency of the differential ring oscillator based on the detected errors, wherein adjusting the frequency involves adjusting a supply voltage for the differential ring oscillator. The system also uses a phase-tracking path to adjust a phase of the differential ring oscillator based on the detected errors, wherein adjusting the phase involves selectively activating an injection pulse generator to inject pulses into the differential ring oscillator. Finally, the system uses a gating mechanism to periodically suppress the injected pulses produced by the injection pulse generator to enable the frequency-tracking path to detect and remediate frequency errors without interference from phase adjustments.

Injection-locking PLL with frequency drift tracking and duty-cycle distortion cancellation

In the optical device, a ring-resonator modulator, having an adjustable resonance (center) wavelength, optically couples an optical signal that includes the carrier wavelength from an input optical waveguide to an output optical waveguide. A monitoring mechanism in the optical device, which is optically coupled to the output optical waveguide, monitors a performance metric of an output optical signal from the output waveguide. For example, the monitoring mechanism may monitor: an average optical power associated with the output optical signal, and/or an amplitude of the output optical signal. Moreover, control logic in the optical device adjusts the resonance wavelength based on the monitored performance metric so that the performance metric is optimized.

Wavelength-locking a ring-resonator modulator

An optical receiver includes a feedback circuit that applies a feedback signal to a front-end circuit prior to the front-end circuit converting an optical signal into an analog electrical signal. In particular, the optical receiver includes a digital slicer that determines a digital electrical signal from the analog electrical signal based on a reference voltage that specifies a decision threshold and a clock that specifies sampling times. The feedback circuit determines the feedback signal at least one previous bit preceding a current bit in the analog electrical signal that is provided by the digital slicer and an impulse response of a communication channel. Moreover, the feedback signal has a pulse width that is less than a bit time of the clock. In this way, the optical receiver can cancel post-cursors of the current bit, even when the communication channel includes a low-pass filter.

Optical receiver with adjustable pulse-width feedback

The disclosed embodiments provide a system that tracks and compensates for input signal noise at a receiver of a data communication channel. In particular embodiments, the receiver of the data communication link receives an input signal which comprises two signal levels. Next, for each of the two signal levels, the system generates an error signal by comparing the input signal value of the signal level with an expected signal value for the signal level. The system then updates a threshold signal value based on at least one of the two error signals associated with the two signal levels. Finally, the system compensates for input signal noise in the received input signal using the updated threshold signal value.

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San Mateo, CA, United States of America

Eric Y Chang