A first clock signal is generated from a reference clock signal. A first frequency associated with the first clock signal is less than a reference clock frequency associated with the reference clock signal. The first clock signal is propagated towards a first component of an integrated circuit through a clock tree. A second clock signal having a second frequency is generated from the first clock signal at a terminal point of the clock tree. The second clock signal is provided to the first component.

A clock and data recovery circuit includes a phase detector (PD), a phase frequency detector (PFD), a multiplexer circuit, a conversion stage and an oscillator. The PD detects a difference in phase between a data signal and an oscillating signal to generate a first set of error signals. The PFD detects a difference in phase and frequency between a reference clock signal and the oscillating signal to generate a second set of error signals. The multiplexer circuit selectively outputs the first set of error signals or the second set of error signals as a third set of error signals according to a selection signal. The conversion stage determines a set of gains according to the selection signal, and converts the third set of error signals with the set of gains to generate a set of input signals. The oscillator generates the oscillating signal according to the set of input signals.

In accordance with an embodiment, a method of operating a fractional-N phase locked loop (FN-PLL) includes: dividing a first clock signal using a multi-modulus divider (MMD) based on a modulus control signal to form a frequency-divided clock signal, where the first clock signal is based on an output clock of the PLL; generating the modulus control signal based on a divider control input value using a delta-sigma modulator (DSM); and when a fractional portion of the divider control input value is within a first range of values, and repeatedly removing a first number of clock cycles from the first clock signal before dividing the first clock signal using the MMD, where the first number of clock cycles is a non-integer number of clock cycles.

An apparatus includes a phase-locked loop and a jitter detection circuit. A method of detecting a jitter in the apparatus includes the phase-locked loop generating a lead control signal and a lag control signal according to a reference clock and a feedback clock, the jitter detection circuit generating a jitter signal according to the lead control signal and the lag control signal, the jitter detection circuit generating a jitter window signal according to the jitter signal, the jitter detection circuit identifying jitters in the clock signal according to the jitter signal and the jitter window signal, and the jitter detection circuit outputting a jitter indication signal according to the number of jitters identified.

A phase locked loop (PLL) comprises: a reference oscillator to generate a reference clock having a reference frequency; a voltage controlled oscillator (VCO) to generate a VCO clock having a VCO frequency controlled in response to a control signal applied to the VCO; a first integrator to integrate the reference frequency into a first ramp slope; a second integrator to integrate the VCO frequency into a second ramp slope; and a slope comparator to generate a slope difference between the first ramp slope and the second ramp slope and that is conveyed by the control signal, such that the control signal is configured to drive the VCO frequency toward the reference frequency to minimize the slope difference and frequency lock the VCO frequency to the reference frequency.

A reference-less dock and data recovery device includes a CDR circuit, an oscillator circuit, and a processor. The CDR circuit is configured to generate a first clock signal through synchronization according to a data signal having a first frequency in a first time period. The oscillator circuit is configured to output an oscillating clock signal according to the first clock signal, A frequency of the oscillating clock signal is substantially identical to that of the first clock signal. The processor oversamples the data signal having a second frequency in a second time period to generate a simulated preparation signal conforming to the second frequency. The CDR circuit is configured to generate a second clock signal through synchronization according to the simulated preparation signal. Before generating the second clock signal, the CDR circuit is synchronized to the oscillating clock signal to maintain outputting of the first clock signal.

Apparatus and methods for phasing detection of asynchronous dividers are provided herein. In certain embodiments, a clock and data recovery system includes a first divider that outputs a first divided clock signal, a second divider that outputs a second divided clock signal, and an asynchronous clock phasing detection circuit that generates a detection signal indicating a relative phase difference between the first divided clock signal and the second divided clock signal. The asynchronous clock phasing detection circuit includes a quantization and logic circuit that generates an output signal indicating when the first divided clock signal and the second divided clock signal are in different states, an oscillator that outputs a control clock signal, a first counter controlled by the control clock signal and configured to count the output signal, and a control circuit that processes a first count signal from the first counter to generate the detection signal.

Embodiments of the present invention synchronize multiple synthesizers, such as phase-locked loops (PLLs), in a manner that does not require communication or coordination between the synthesizers. Specifically, each synthesizer is part of a synthesizer circuit that includes a synthesizer (e.g., a PLL), a phase measurement circuit, and a synchronization circuit. A common reference signal (e.g., an alternating clock signal) is provided to the synthesizer circuits. In one exemplary embodiment, in each synthesizer circuit, the phase measurement circuit measures a phase difference between the reference signal and a corresponding output of the synthesizer, and the synchronization circuit adjusts the synthesizer operation based on the measured phase difference in such a way that all of the synthesizers operate in-phase with one another relative to the common reference signal, without having any communication or coordination between the two synthesizer circuits other than provision of the common reference signal.

Introduced here are techniques for implementing a clock and data recovery circuit with improved tendencies, such a pull up and/or pull down tendencies. In various embodiments, the CDR circuit includes a phase detector that receives an input signal and a output reference clock signal. The phase detector then outputs two signals to charge pump. The output from the charge pump drives an oscillator control voltage up or down depending the current from the charge pump. A lock detector detects whether a lock has occurred by comparing the oscillator control voltage to a predetermined threshold voltage. A lock can occur when the circuit has settled into a frequency substantially near the frequency of the input signal and the oscillator control voltage is substantially near the threshold voltage. A controller circuit can control a sweeping of an available frequency range by the circuit until a lock occurs.

Disclosed is a phase demodulator, which includes a transmitter that outputs a reference signal to a target, a receiver that receives a target signal generated in response to the reference signal from the target, and a demodulation processor that demodulates the target signal, and the demodulation processor includes a phase controller that outputs a first phase signal based on the reference signal, a phase shifter that delays a phase of the first phase signal to output a first delayed signal, a mixer that outputs a first mixing signal based on the target signal and the first delay signal, and an amplifier that outputs a first feedback signal generated by amplifying the first mixing signal to the phase controller.