Altera Corporation

Farhad Zarkeshvari

Tad Kwasniewski

A phase-locked loop includes a phase-to-digital converter that receives a first periodic input signal at a first input and a first feedback signal at a second input. The phase-to-digital converter generates digital signals. A digitally controlled oscillator includes a delay-locked loop that is responsive to the digital signals. The delay-locked loop generates a periodic output signal having an average frequency that is a product of a frequency of the first periodic input signal multiplied by a non-integer fractional number while a phase of the first periodic input signal is unchanging.

Fractional delay-locked loops

Phase detection circuitry in a delay-locked loop compares a periodic input signal to a feedback signal. The phase detection circuitry generates a delay signal that controls delays of the delay circuits. Two or more output signals of the delay circuits are transmitted to an input of the phase detection circuitry. The delay-locked loop can be configured so that the period of the periodic input signal divided by a delay of one of the delay circuits equals a non-integer rational number when the phase and frequency of the periodic input signal are constant. A frequency multiplier can be coupled to the delay circuits to generate a periodic output signal. The periodic output signal has an average frequency that is a product of the frequency of the periodic input signal multiplied by a fractional non-integer number when the phase and frequency of the periodic input signal are constant.

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Durham, NC, United States of America

Farhad Zarkeshvari