Embodiments of the present disclosure provide systems and methods for realizing phase synchronization updates based on an input system reference signal SYSREF without the need to synchronously distribute the SYSREF signal on a high-speed domain. In particular, phase synchronization mechanisms of the present disclosure are based on keeping a first phase accumulator in the device clock domain and using a second phase accumulator in the final digital clock domain to asynchronously transmit phase updates to the final digital clock domain. Arrival of a new SYSREF pulse may be detected based on the counter value of the first phase accumulator, which value is asynchronously transferred and scaled to the second phase accumulator downstream. In this manner, even though the SYSREF signal itself is not synchronously transferred to the second phase accumulator, the phase updates from the SYSREF signal may be transferred downstream so that the final phase may be generated deterministically.

Embodiments of the present disclosure provide systems and methods for realizing phase synchronization updates based on an input system reference signal SYSREF without the need to synchronously distribute the SYSREF signal on a high-speed domain. In particular, phase synchronization mechanisms of the present disclosure are based on keeping a first phase accumulator in the device clock domain and using a second phase accumulator in the final digital clock domain to asynchronously transmit phase updates to the final digital clock domain. Arrival of a new SYSREF pulse may be detected based on the counter value of the first phase accumulator, which value is asynchronously transferred and scaled to the second phase accumulator downstream. In this manner, even though the SYSREF signal itself is not synchronously transferred to the second phase accumulator, the phase updates from the SYSREF signal may be transferred downstream so that the final phase may be generated deterministically.

Presented herein are techniques for implementing a differential sub-sampling phase locked loop (PLL). A method includes detecting a common-mode voltage on an output of a differential sub-sampling phase detector operating in the differential sub-sampling phase locked loop, and controlling, based on the common-mode voltage, a duty cycle of a feedback signal of the differential sub-sampling phase locked loop that is fed back to the differential sub-sampling phase detector.

Presented herein are techniques for implementing a differential sub-sampling phase locked loop (PLL). A method includes detecting a common-mode voltage on an output of a differential sub-sampling phase detector operating in the differential sub-sampling phase locked loop, and controlling, based on the common-mode voltage, a duty cycle of a feedback signal of the differential sub-sampling phase locked loop that is fed back to the differential sub-sampling phase detector.

A clock and data recovery circuit includes a sampling circuit, a phase detector, a first processing circuit, a second processing circuit and an oscillator circuit. The sampling circuit is configured to sample input data according to an output clock, and generate a sampling result. The phase detector is configured to generate a detection result according to the sampling result. The first processing circuit is configured to process the sampling result to generate a first digital code. The second processing circuit is configured to accumulate a portion of the first digital code to generate a second digital code. A rate of change of a code value of the second digital code is slower than a rate of change of a code value of the first digital code. The oscillator circuit is configured to generate the output clock according to the detection result, the first digital code and the second digital code.

A clock and data recovery circuit includes a sampling circuit, a phase detector, a first processing circuit, a second processing circuit and an oscillator circuit. The sampling circuit is configured to sample input data according to an output clock, and generate a sampling result. The phase detector is configured to generate a detection result according to the sampling result. The first processing circuit is configured to process the sampling result to generate a first digital code. The second processing circuit is configured to accumulate a portion of the first digital code to generate a second digital code. A rate of change of a code value of the second digital code is slower than a rate of change of a code value of the first digital code. The oscillator circuit is configured to generate the output clock according to the detection result, the first digital code and the second digital code.

Presented herein are techniques for implementing a differential sub-sampling phase locked loop (PLL). A method includes detecting a common-mode voltage on an output of a differential sub-sampling phase detector operating in the differential sub-sampling phase locked loop, and controlling, based on the common-mode voltage, a duty cycle of a feedback signal of the differential sub-sampling phase locked loop that is fed back to the differential sub-sampling phase detector.

Presented herein are techniques for implementing a differential sub-sampling phase locked loop (PLL). A method includes detecting a common-mode voltage on an output of a differential sub-sampling phase detector operating in the differential sub-sampling phase locked loop, and controlling, based on the common-mode voltage, a duty cycle of a feedback signal of the differential sub-sampling phase locked loop that is fed back to the differential sub-sampling phase detector.

According to an exemplary embodiment of the present disclosure, a fractional-N sub-sampling phase locked loop using a phase rotator includes a frequency locked loop which is locked at a fractional-N frequency using a delta-signal modulator and a sub-sampling phase locked loop which locks a phase to a fractional multiple using a phase rotator, and the phase rotator applies a fractional multiple to a phase of a signal output from the oscillator.

The present invention discloses a clock data recovery method having quick locking and bandwidth stabilizing mechanism used in a clock data recovery circuit. A relative position relation between a serial data and a sampling clock is detected by a phase detection circuit in an adaptive control period to generate a tracking direction. The tracking direction of a first clock period is directly outputted as an adaptive tracking direction by an adaptive tracking circuit. For each of the clock periods behind the first clock period, a previous tracking direction is replaced by a current tracking direction only when the current tracking direction exists and is different from the previous tracking direction of a previous clock period such that an actual tracking direction is generated when the adaptive tracking direction changes. The phase of the sampling clock is adjusted according to the actual tracking direction by a clock control circuit.