Apple Inc.

Samed Maltabas

Dennis M Fischette, Jr

Yu Cheng Chen

Meei-Ling Chiang

Boon-Aik Ang

Shaobo Liu

Khaled M Alashmouny

Charles L Wang

Wei Deng

Yu Chen

Dabin Zhang

Yikun Chang

Litesh Sajnani

Hairong Yu

Gregory N Santos

Richard Y Su

Pyoungwon Park

A clock generator circuit may include a multiplex circuit and a phase-locked loop circuit. The multiplex circuit may generate a reference clock signal for the phase-locked loop circuit by selecting one of different clock signals. In response to a switch of the reference clock signal from one clock signal to another, the phase-locked loop circuit may disable phase-locking and enter into a frequency acquisition mode during which the frequency of the phase-locked loop circuit's output clock signal is adjusted based on the frequency of the newly selected reference clock signal. After a period of time has elapsed, the phase-locked loop circuit returns to phase-locking operation.

Reference clock switching in phase-locked loop circuits

Systems, apparatuses, and methods for implementing a hybrid asynchronous gray counter with a non-gray zone detector are described. A circuit includes an asynchronous gray counter coupled to control logic. The control logic programs the asynchronous gray counter to operate in different modes to perform various functions associated with a high-performance phase-locked loop (PLL). In a first mode, the asynchronous gray counter serves as a frequency detector to count oscillator cycles within a reference clock cycle. In a second mode, the asynchronous gray counter serves as a coarse phase detector to detect a phase error between a feedback clock and a reference clock. In a third mode, the asynchronous gray counter serves as a multi-modulus divider to divide an oscillator clock down to create a feedback clock. Using a single asynchronous gray counter for three separate functions reduces power consumption and area utilization.

Hybrid asynchronous gray counter with non-gray zone detector for high performance phase-locked loops

A system and method for efficient on-chip monitoring of clock signals post-silicon. An electronic circuit includes a post-silicon and on-die signal monitor and a first signal generator that sends a first signal with a first signal period to the signal monitor. The signal monitor selects a first sampling signal with a first sampling period such that a ratio of the first sampling period to the first signal period is greater than one and is a non-integer. The signal monitor selects a reference voltage level for indicating when the first signal is asserted. When the first sampling period has elapsed, the signal monitor samples the first signal to generate a voltage level, and upon completing sampling, determines a duty cycle of the generated voltage levels, which indicates a duty cycle of the first signal. Using a similar approach, the signal monitor is also capable of determining skew between two signals.

Duty cycle and skew measurement and correction for differential and single-ended clock signals

A clock signal generated by a fractional-N phase-locked loop circuit may include deterministic jitter resulting from a sigma-delta modulation of a frequency divisor used by a divider circuit. In order to reduce such jitter, a cancelation circuit is employed that can generate a feedback signal by delaying an output signal from the divider circuit, where the amount of delay applied to the output signal is based on an accumulated phase residue from the modulation of the frequency divisor. The resultant feedback signal is compared to a reference signal, results of which are used to adjust an oscillator circuit generating the clock signal, thereby reducing the deterministic jitter.

Spur cancelation in phase-locked loops using a reconfigurable digital-to-time converter

A clock test system included in a computer system includes a clock generator circuit that generates multiple clock signals. A switch circuit selects different ones of the multiple clock signals during different time periods to generate an output clock signal. A measurement circuit measures a duty cycle of the output clock signals during the different time periods to generate multiple duty cycle measures. The measurement circuit uses the multiple duty cycle measurements to cancel a portion of duty cycle distortion in the output clock signal to determine an adjusted duty cycle value.

Reconfigurable clock flipping scheme for duty cycle measurement

A phase-locked loop circuit included in a computer system includes time-to-digital converter and digital-to-time converter circuits. During a mode to test the time-to-digital converter circuit, the digital-to-time converter circuit is coupled to the time-to-digital converter circuit in a loop-back fashion. A control circuit supplies stimulus codes to the digital-time-converter circuit, which generates multiple delayed versions of a reference clock signal using the stimulus codes. The time-to-digital converter circuit, in turn, generates capture codes based on the delay between the reference clock signal and the delayed versions of the reference clock signal. The control circuit compares the capture codes to the stimulus codes to determine a linearity of a response of the time-to-digital converter circuit.

Time-to-digital converter circuit linearity test mechanism

A digital PLL is disclosed. In one embodiment, the digital PLL includes a TDC coupled to receive a reference clock signal and feedback signal. The TDC includes a chain of serially-coupled delay elements. An oscillator in the PLL is configured to generate a periodic output signal. A divider is coupled to receive the periodic output signal and generate the feedback signal provided to the TDC. The digital PLL also includes a control circuit. During a phase-locking procedure, each of the serially-coupled delay elements is enabled for fast phase capture. However, once phase-lock has been detected by observing TDC output code, the control circuit is adaptively configured to disable all but a subset of the delay elements for saving power.

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Santa Clara, CA, United States of America

Samed Maltabas