A frequency synthesizer includes: an oscillating section that generates a first signal; a frequency ratio measuring section that measures a frequency ratio of the first signal and a second signal by using the first signal and the second signal; a comparing section that compares the frequency ratio, which is measured by the frequency measuring section, with a target value of a frequency ratio; and a filter that is disposed on a preceding stage of the comparing section. A frequency of the first signal of the oscillating section is adjusted on the basis of a comparison result of the comparing section.

A phase-locked loop according to the present disclosure includes a reference-phase generation circuit that sequentially generates a reference phase value, and an oscillating circuit that generates a first clock on a basis of a difference between the reference phase value and a feedback phase value. The phase-locked loop further includes a signal generation circuit that generates, on a basis of the first clock, a plurality of second clocks varying in phase, and generates a third clock by switching the plurality of second clocks a plurality of times in each of cycle periods each corresponding to one cycle of the reference clock. The phase-locked loop further includes a phase detection circuit that determines a phase value of the third clock and outputs the determined phase value as the feedback phase value.

An interpolative divider includes a look ahead sigma delta modulator circuit to generate divide values according to a divide ratio. A plurality of M storage elements are coupled to the sigma delta modulator to store the divide values, M being at least 2. A selector circuit selects the respective divide values and supplies the divide values to a portion of an interpolative divider circuit, the portion including a divider and a phase interpolator. The interpolative divider generates an output clock signal having a first clock period that may be determined by the first and second divide values. The M storage elements are loaded by a clock signal that is slower than the output clock signal by at least half.

A clock synthesizer for synthesizing an output clock locked to a selected reference clock input has a pair of phase locked loops locked to respective reference clock inputs first generating first and second frequencies. One of the frequencies is selected to control a controlled oscillator for generating an output clock. The frequency offset between the first and second frequencies at the time of switching is stored and added to the frequency controlling the controlled oscillator.

A frequency synthesizing device includes a voltage-controlled oscillator receiving an adjusting signal and generating an output signal according to the adjusting signal. A feedback frequency divider having a plurality of divisor values receives the output signal and generates a feedback signal after performing frequency dividing. An automatic frequency calibration circuit of the frequency synthesizing device includes a first frequency divider receiving a reference frequency, and a second frequency divider receiving the feedback signal. A comparator of the automatic frequency calibration circuit receives and compares outputs from the first frequency divider and the second frequency divider in a predetermined period to generate a comparing result. A state machine outputs the adjusting signal according to the comparing result in a calibration mode.

A signal source with a wireless frequency reference. A signal loop includes an amplifier and a coupler. The magnitude of the loop gain in the signal loop is substantially equal to 1 at a steady-state amplitude of a signal at a fundamental frequency. A reference oscillator is coupled to the loop through the coupler, via a wireless link, and provides phase stabilization. The loop may include a nonlinear transmission line, to generate a comb output spectrum.

A frequency synthesis system and a frequency generation method of microwave photons based on photoelectric synergy are provided, the system includes an optical frequency comb for generating narrow optical pulse signals with high stability and low phase noise through; an optical frequency doubling/dividing unit for performing frequency doubling or frequency dividing on a repetition frequency of the narrow optical pulse signals output by the optical frequency comb; a photoelectric conversion unit for performing photoelectric conversion on input optical pulse signals, and outputting an electrical frequency comb; a second electrical filter unit for filtering input electrical signals; and a second electrical amplifying unit for performing power amplification on the input electrical signals. An operation frequency and performance of the optical frequency comb is three orders of magnitude or higher than that of common microwave frequency sources, microwave frequency signals with larger frequency range and better performance can be generated.

A frequency synthesis system and a frequency generation method of microwave photons based on photoelectric synergy are provided, the system includes an optical frequency comb for generating narrow optical pulse signals with high stability and low phase noise through; an optical frequency doubling/dividing unit for performing frequency doubling or frequency dividing on a repetition frequency of the narrow optical pulse signals output by the optical frequency comb; a photoelectric conversion unit for performing photoelectric conversion on input optical pulse signals, and outputting an electrical frequency comb; a second electrical filter unit for filtering input electrical signals; and a second electrical amplifying unit for performing power amplification on the input electrical signals. An operation frequency and performance of the optical frequency comb is three orders of magnitude or higher than that of common microwave frequency sources, microwave frequency signals with larger frequency range and better performance can be generated.

The present invention provides a frequency synthesizer that is switchable at a high speed and includes a few unnecessary frequency components in an output frequency signal. In a frequency synthesizer 1, a DDS 2 operates based on a clock signal to generate a reference frequency signal with a predetermined reference frequency, and clock signal supply units 41 and 42 switch the clock signals that have different clock frequencies to supply to the DDS 2. When the clock signals are switched to operate the DDS 2, the storage unit 12 stores a combination of a clock frequency f.sub.clk, a reference frequency f.sub.c, and a dividing number N in association with an output frequency f.sub.VCO of the frequency synthesizer 1 such that a spurious frequency does not exist within a predetermined frequency range and a dividing number of a variable frequency divider 302 disposed on a PLL circuit 3 is minimum. Setting units 11 and 24 read setting items stored in the storage unit 12 to set respective units.

Octagonal phase rotator apparatus is provided for producing an output signal that is phase dependent on a digital control code. The apparatus includes an I-mixer, a Q-mixer, and first and second IQ-mixers. The I-mixer is responsive to I-control bits of the digital control code. The Q-mixer is responsive to Q-control bits of the digital control code. The first and second IQ-mixers are respectively responsive to one or more IQ1-control bits and one or more IQ2-control bits of the digital control code. The I-mixer comprises an I-DAC for steering current between a positive phase IP and a negative phase IN of an in-phase (I) signal wherein the one or more I-control bits control switching of a first current unit between IP and IN, and a set of amplifiers for weighting the phases IP and IN, in dependence on current steered to each phase by the I-DAC, to produce a weighted I-signal.