Disclosed is a low-power fractional-N phase-locked loop circuit, which comprises a phase detector, a voltage-to-current converter, a loop filter, a voltage-controlled oscillator, a frequency divider and a digital logic processor; the phase detector, the voltage-to-current converter, the loop filter, the voltage-controlled oscillator and the frequency divider are connected in sequence; a reference signal is input from the phase detector, the phase detector detects the phases of the reference signal and a feedback signal with a quantization error output by the frequency divider, compensates a quantization phase error generated by fractional frequency division, and outputs a compensated phase detection result to the voltage-to-current converter; the quantization error generated by fractional frequency division is converted into a voltage domain through a digital domain or directly coupled to a phase error signal in the phase detector to complete the compensation of the quantization error.

A digital phase-locked loop (DPLL) includes a time-to-digital converter (TDC) to generate a multi-bit code based on a phase error between a reference clock and a feedback clock, a digital loop filter (DLF) coupled to the TDC, a digitally-controlled oscillator (DCO) circuit coupled to the DLF and to generate an output signal that is convertible to the feedback clock, and a logic component coupled to an input of the DCO circuit. The logic component is to: trigger, in response to detecting a power on of the DPLL circuit, a switch to decouple the DLF from the DCO circuit; determine, from the reference clock, a target frequency; measure a frequency of the feedback clock; and iteratively generate, based on the frequency during each iteration, a set of digital bits to the input of the DCO circuit that successively causes the frequency to converge towards the target frequency.

A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation includes initially establishing, using a first calibration method where a data bit pattern received by the data interface circuit is predictable, an optimal sampling point for sampling data bits received by the data interface circuit, and during a normal system operation and without disturbing the normal system operation, performing a second calibration method where the data bit pattern received by the data interface circuit is unpredictable. The second calibration method determines an amount of a timing drift for received data bit edge transitions and adjusts the optimal timing point determined by the first calibration method to create a revised optimal timing point. The second calibration method samples fringe timing points associated with the transition edges of a data bit.

A method for operating a data interface circuit whereby calibration adjustments for data bit capture are made without disturbing normal system operation includes initially establishing, using a first calibration method where a data bit pattern received by the data interface circuit is predictable, an optimal sampling point for sampling data bits received by the data interface circuit, and during a normal system operation and without disturbing the normal system operation, performing a second calibration method where the data bit pattern received by the data interface circuit is unpredictable. The second calibration method determines an amount of a timing drift for received data bit edge transitions and adjusts the optimal timing point determined by the first calibration method to create a revised optimal timing point. The second calibration method samples fringe timing points associated with the transition edges of a data bit.

A phased locked loop includes; a load circuit that generates an output signal in response to a driving voltage, a frequency calibration circuit that generates a calibration signal in response to an output frequency of the output signal and a target frequency, and a regulator that generates the driving voltage in response to the calibration signal.

A DLL includes a delay line with two phase outputs, a gater coupled with the delay line phase outputs, a PFD coupled with gater outputs, a PD coupled with PFD outputs, a retimer coupled with PD outputs, and a loop filter with inputs coupled with the retimer and a speed control output coupled with the delay line. The gater passes signals on its two inputs to its two outputs, apart from a first pulse on its first input. The PD determines if the second gated signal leads or lags the first gated signal. The retimer retimes PD output signals to be aligned with a delay line input signal. The loop filter uses the retimed PD output signals to determine if the delay line should delay more or delay less, and outputs a speed control signal to control the delay line speed.

A DLL includes a delay line with two phase outputs, a gater coupled with the delay line phase outputs, a PFD coupled with gater outputs, a PD coupled with PFD outputs, a retimer coupled with PD outputs, and a loop filter with inputs coupled with the retimer and a speed control output coupled with the delay line. The gater passes signals on its two inputs to its two outputs, apart from a first pulse on its first input. The PD determines if the second gated signal leads or lags the first gated signal. The retimer retimes PD output signals to be aligned with a delay line input signal. The loop filter uses the retimed PD output signals to determine if the delay line should delay more or delay less, and outputs a speed control signal to control the delay line speed.

In an embodiment, a method includes initializing an input clock rotating register by sending a reset signal synchronized to an input clock signal and initializing an output clock rotating register by sending the reset signal synchronized to an output clock signal. The method further providing a data input synchronized to the output clock to a plurality of mux-flops. The output clock rotating register activates one of the plurality of mux-flops to receive the data input. The method further includes forwarding the data input via the one of the plurality of mux-flops to a multiplexer. The multiplexer has a selection input of the input clock rotating register. The method further includes selecting the data input as the output of the multiplexer to be a data output signal, such that the data output is synchronized with the input clock.

An initialization circuit of a delay locked loop (DLL) includes a sense circuit and a control circuit. The sense circuit receives an enable signal, a reference clock signal, and various delayed reference clock signals, and outputs another enable signal. The control circuit receives the two enable signals and outputs and provides a control signal to a loop filter of the DLL to control a delay value associated with the DLL. The control signal is provided to the loop filter such that the delay value associated with the DLL equals a predetermined delay value for a predetermined time duration. Further, after a lapse of the predetermined time duration, the delay value associated with the DLL increases until a difference between a time period of the reference clock signal and the delay value equals a threshold value.

An initialization circuit of a delay locked loop (DLL) includes a sense circuit and a control circuit. The sense circuit receives an enable signal, a reference clock signal, and various delayed reference clock signals, and outputs another enable signal. The control circuit receives the two enable signals and outputs and provides a control signal to a loop filter of the DLL to control a delay value associated with the DLL. The control signal is provided to the loop filter such that the delay value associated with the DLL equals a predetermined delay value for a predetermined time duration. Further, after a lapse of the predetermined time duration, the delay value associated with the DLL increases until a difference between a time period of the reference clock signal and the delay value equals a threshold value.