A hybrid Phase Locked Loop, PLL (10, 34A, 34B, 38) employs an analog control loop during a first period of operation, such as steady-state operation, to achieve a simple design, stable operation at very high frequency, and low phase noise. During a second period of operation, such as frequency changes, a digital control loop takes over. Under digital control, charge pump (14) inputs are forced to be at or near 100% duty cycle for maximum loop filter (16) charging and fast, linear frequency change. The digital control loop monitors when the target frequency is reached, and exits the second period of operation with the proper feedback signal phase. The digital control loop can operate in two control modes. In a first mode, the phase of the divided VCO output signal is synchronized with the phase of a periodic reference signal throughout the frequency change. In a second mode, the frequency and phase are controlled in separate steps, by controlling the integer and fractional parts of delta-sigma generated division number. Three embodiments are disclosed. In a first embodiment, a switch substitutes constant charge pump (14) inputs for the outputs of a phase frequency detector, PFD (12) to maximize the loop filter (16) current. In a second embodiment, one pulse of one of the periodic signals is suppressed, forcing the PFD (12) to output charge pump input signals at near 100% duty cycle. In a third embodiment, all the cycles of one of the periodic signals are suppressed, forcing PFD (12) output signals to 100% duty cycle.

Methods and circuits are provided for range extension of a phase-locked loop (PLL). The PLL uses a phase subtractor with a limited unextended range. It also includes first and second registers and combinatorial logic. The phase subtractor calculates the current phase difference. The first register stores the previous phase difference. The combinatorial logic determines, from the current phase difference and the previous phase difference, if a range excursion occurs, and if it is upward or downward. When an upward excursion occurs, the value in the second register is incremented. When a downward excursion occurs, the value of the second register is decremented. The bits in the second register are combined with the bits of the current phase difference to obtain an extended current phase difference.

Dynamic voltage frequency scaling to transition to a target clock frequency and associated target voltage is provided. Dynamic voltage frequency scaling to a different clock frequency is performed by gradually changing the clock frequency using discrete variable-size steps, while dynamically switching to faster or slower reference clock frequencies as appropriate to harmonize the frequency trajectory with system requirements.

A PLL includes a controlled oscillator, a phase accumulator to measure the controlled oscillator output phase, a phase predictor to calculate the required output phase, and a phase subtractor to calculate the phase difference or phase error. The phase accumulator includes a counter whose output sequence changes only one bit per counted controlled oscillator output cycle, such as a Gray counter. It further includes a register or latches, which sample(s) the counter output value upon receiving a reference clock pulse. The latches output value represents the measured phase. A binary encoder, such as a Gray-to-binary converter, may translate the measured phase to a binary number. The phase accumulator may further include a delay line, second latches, and a delay line decoder to measure a fractional part of the phase. A calibration feedback loop may keep the number of delay line steps per output clock pulse known and stable.

A PLL has a frequency comparator that is active during lock-in. It outputs a signal related to the difference between the oscillator frequency and a target frequency. It captures an initial phase and observes change in phase relative to the initial phase. Two ways of capturing the initial phase are provided. The frequency comparator can provide input signals for the loop filter and make the PLL act as a frequency-locked loop during lock-in. Alternatively, it can provide input signals for a search controller that may perform a binary or other search. The frequency comparator may wait one or more cycles of the reference clock signal to reduce noise, or it may set a threshold to eliminate some noise. It may signal that the oscillator frequency equals the target frequency when the threshold has not been exceeded after a timeout. The search controller may directly or indirectly control the PLL's oscillator.

A method of performing a frequency scan at a radio includes placing the radio in an active mode and, while maintaining the radio in the active mode, for each of a plurality of target frequencies determining a coarse frequency tuning value based on the target frequency. The radio places a phase locked loop (PLL) in an open-loop configuration and while the PLL is in the open-loop configuration, programs the VCO with the coarse frequency tuning value. The radio programs the divider with a feedback adjustment based on the target frequency, places the PLL in a closed-loop configuration, and in response to the PLL reaching a settled state, performs an operation based on an output signal of the PLL.

A method includes generating first frequency metrics for a first received network clock signal using a local reference clock signal. The method includes, in response to the first received network clock signal being available and satisfying a quality metric, generating a network delay estimate using a first error estimate based on the first received network clock signal, and updating stored frequency metrics for the first received network clock signal with the first frequency metrics. The method includes generating an output clock signal based on received packets and the network delay estimate. The first frequency metrics for the first received network clock signal may include a current average frequency count, a prior average frequency count, a standard deviation of prior average frequency counts and a multiplicative constant corresponding to a number of samples used to determine the current average frequency count, prior average frequency count, and standard deviation.

A method of performing a frequency scan at a radio includes placing the radio in an active mode and, while maintaining the radio in the active mode, for each of a plurality of target frequencies determining a coarse frequency tuning value based on the target frequency. The radio places a phase locked loop (PLL) in an open-loop configuration and while the PLL is in the open-loop configuration, programs the VCO with the coarse frequency tuning value. The radio programs the divider with a feedback adjustment based on the target frequency, places the PLL in a closed-loop configuration, and in response to the PLL reaching a settled state, performs an operation based on an output signal of the PLL.

A PLL includes a controlled oscillator, a phase accumulator to measure the controlled oscillator output phase, a phase predictor to calculate the required output phase, and a phase subtractor to calculate the phase difference or phase error. The phase accumulator includes a fast counter and a low-power counter, and two sets of corresponding latches. The fast counter counts cycles of the controlled oscillator clock signal, and the low-power counter counts carry signals from the fast counter. The low-power counter represents one or more most significant bits of the integer part of the measured phase, and the fast counter represents the remaining bits. The phase accumulator may further include a delay line, second latches, and a delay line decoder to measure a fractional part of the phase. A calibration feedback loop may keep the number of delay line steps per output clock pulse known and stable.

A PLL has a controlled oscillator with a limited frequency range. It has a phase accumulator and a phase predictor whose ranges are limited to a value K related to their bit width. K is less than the ratio of the maximum output frequency and the minimum reference frequency. The PLL locks the output frequency to a value higher than the FCW times the reference frequency. The PLL includes a means for setting the output frequency to a target frequency before achieving final lock. The PLL may have a lock detector. After acquiring lock, the PLL may reduce the bit width and K value, for example by cutting power to or switching off some of the bits, or by switching off slow counters in a multi-counter system.