A delay locked loop circuit includes a first delay locked loop and a second delay locked loop having different characteristics. The first delay locked loop performs a delay-locking operation on a reference clock signal to generate a delay locked clock signal. The second delay locked loop performs a delay-locking operation on the delay locked clock signal to generate an internal clock signal.

A delay locked loop circuit includes a first delay locked loop and a second delay locked loop having different characteristics. The first delay locked loop performs a delay-locking operation on a reference clock signal to generate a delay locked clock signal. The second delay locked loop performs a delay-locking operation on the delay locked clock signal to generate an internal clock signal.

A system, a method and a built-in phase noise measurement apparatus are introduced. The built-in phase noise measurement apparatus includes a first DLL and a TDC, in which the first DLL circuit controls a delay of a first signal to generate a second signal based on a control code, tune the control code until a phase of the second signal is aligned to a phase of a reference clock signal, and record a value of the control code when the phase of the second signal is aligned to the phase of the reference clock signal. The DLL circuit controls the delay of the first signal based on the value of the control code after the phase of the second signal is aligned to the phase of the reference clock signal. The TDC determines the phase noise of the first signal based on the reference clock signal and the second signal.

A system, a method and a built-in phase noise measurement apparatus are introduced. The built-in phase noise measurement apparatus includes a first DLL and a TDC, in which the first DLL circuit controls a delay of a first signal to generate a second signal based on a control code, tune the control code until a phase of the second signal is aligned to a phase of a reference clock signal, and record a value of the control code when the phase of the second signal is aligned to the phase of the reference clock signal. The DLL circuit controls the delay of the first signal based on the value of the control code after the phase of the second signal is aligned to the phase of the reference clock signal. The TDC determines the phase noise of the first signal based on the reference clock signal and the second signal.

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.

An interpolator includes a first delay circuit, a second delay circuit, and a tunable delay circuit. The first delay circuit delays a first input signal for a fixed delay time, so as generate a first output signal. The second delay circuit delays a second input signal for the fixed delay time, so as to generate a second output signal. The tunable delay circuit delays the first input signal for a tunable delay time, so as to generate an output interpolation signal. The tunable delay time is determined according to the first output signal, the second output signal, and the output interpolation signal.

A system and method for a frequency detector circuit includes: a transition detector configured to receive a data input and provide a first edge output based on transitions in the data input; a first circuit configured to generate a second edge output; a second circuit configured to generate a third edge output; and a combinational logic configured to output an UP output when at least two of the first edge output, the second edge output, and the third edge output are high and configured to output a DOWN output when the first edge output, the second edge output, and the third edge output are all low.

A system and method for a frequency detector circuit includes: a transition detector configured to receive a data input and provide a first edge output based on transitions in the data input; a first circuit configured to generate a second edge output; a second circuit configured to generate a third edge output; and a combinational logic configured to output an UP output when at least two of the first edge output, the second edge output, and the third edge output are high and configured to output a DOWN output when the first edge output, the second edge output, and the third edge output are all low.

A system and method for correcting for phase errors, in a phase locked loop, resulting from spread spectrum clocking involving a reference clock signal having a frequency modulation. A correction generation circuit generates an offset signal, that when injected after the charge pump of the phase locked loop, causes the voltage controlled oscillator to produce a signal with substantially the same frequency modulation, thereby reducing the phase error. The correction generation circuit may include a timing estimation circuit for estimating the times at which transitions (between positive-sloping and negative-sloping portions of the triangle wave) occur, and an amplitude estimation circuit for estimating the amplitude of the offset signal that results in a reduction in the phase error.

A clock generator receives first and second clock signals, and input representing a desired frequency ratio. A comparison is made between frequencies of an output clock signal and the first clock signal, and a first error signal represents the difference between the desired frequency ratio and this comparison result. The first error signal is filtered. A comparison is made between frequencies of the output clock signal and the second clock signal, and a second error signal represents the difference between the filtered first error signal and this comparison result. The second error signal is filtered. A numerically controlled oscillator receives the filtered second error signal and generates an output clock signal. As a result, the output clock signal has the jitter characteristics of the first input clock signal over a useful range of jitter frequencies and the frequency accuracy of the second input clock signal.