Abstract: A digitally controlled oscillator has a high-order ?? modulator configured to be of at least an order higher than a first order and configured to input a digital control signal and output a pseudorandom digital output signal, a first-order ?? modulator configured to input the pseudorandom digital output signal and generate a control pulse signal including a pulse width corresponding to the pseudorandom digital output signal, a low pass filter configured to pass a low frequency component of the control pulse signal, and an oscillator configured to generate a high-frequency output signal whose frequency is controlled based on the control pulse signal outputted by the low pass filter so as to be a frequency corresponding to the digital control signal.

Abstract: A divider has a clock generation circuit which combines a first trigger clock and a second trigger clock having a first phase difference, so as to generate a third clock having pulse edges corresponding to pulse edges of the first trigger clock and the second trigger clock; an output dividing circuit which divides the frequency of the third clock in half so as to generate a first differential output clock and a second differential output clock having a duty ratio corresponding to the first phase difference; and a phase correction circuit which detects a phase of the first output clock or the second output clock at a timing of the pulse edge of the first trigger clock or the second trigger clock, so as to generate a phase correction signal for resetting the output dividing circuit when the detected phase is not a normal phase.

Abstract: A divider has a clock generation circuit which combines a first trigger clock and a second trigger clock having a first phase difference, so as to generate a third clock having pulse edges corresponding to pulse edges of the first trigger clock and the second trigger clock; an output dividing circuit which divides the frequency of the third clock in half so as to generate a first differential output clock and a second differential output clock having a duty ratio corresponding to the first phase difference; and a phase correction circuit which detects a phase of the first output clock or the second output clock at a timing of the pulse edge of the first trigger clock or the second trigger clock, so as to generate a phase correction signal for resetting the output dividing circuit when the detected phase is not a normal phase.

Abstract: In a frequency dividing device, a 1/P frequency divider subjects an input clock signal to 1/P frequency division. A phase shifter shifts the phase of the 1/P frequency signal and outputs multiple different Q-phase signals. A switch controls phase shifting in accordance with a division ratio control signal, to switch the Q-phase signals from one to another. A 1/R frequency divider subjects the output from the switch to 1/R frequency division and outputs an Rth frequency clock signal. A ½ frequency divider subjects the Rth frequency clock signal to ½ frequency division and outputs a frequency divided clock signal. A division ratio setter receives a division ratio set signal and generates the division ratio control signal. As a division ratio, P×R×2?2×P/Q, P×R×2?P/Q, P×R×2, P×R×2+P/Q, and P×R×2+2×P/Q can be set.

Abstract: A frequency measurement circuit includes: a first counter that counts a number of edges of a clock signal; a counter latch circuit that stores a first count value of the first counter in response to a reference edge corresponding to a reference clock; a first delay circuit that includes a plurality of first unit delay circuits coupled in series and receives the clock signal; a plurality of first delay latch circuits that latch a respective output among the plurality of first unit delay circuits; a first edge detection circuit that detects the edge in the first delay circuit based on the outputs of the plurality of first delay latch circuits; and a first calculator that calculates a cycle or a frequency of the clock signal based on the first count value between two reference edges and position information corresponding to a edge detected between the two reference edges.

Abstract: A phase difference detector for detecting a phase difference between input clocks which both have a same first frequency, including: a pulse width conversion unit for converting the input clocks into a phase difference signal indicating by a pulse width a phase difference between the input clocks; and a counter unit which samples a level of the phase difference signal using a reference clock having a second frequency which is slower than the first frequency, and counts the number of levels of the phase difference signal using a first weighting according to the sampled level of the phase difference signal. When the count value of the counter unit transits in a predetermined range, the phase difference between the input clocks is detected according to the first weighting.

Abstract: A clock selection circuit and synthesizer that is capable of selecting an optimum clock signal from among a plurality of clock signals in a short time. A reference-clock counter counts clock pulses in an inputted reference clock signal (REF). A clock counter counts clock pulses in one of the plurality of clock signals which is selected by a selection unit and frequency-divided by a frequency divider. An instruction-signal output unit outputs a plurality of comparison-instruction signals during an interval in which a difference occurs between the counts of two of the plurality of clock signals having the closest frequencies. A comparison unit compares the count of the reference-clock counter and the count of the clock counter. The selection unit selects a clock signal by a binary search according to the result of the comparison.

Abstract: A clock signal output circuit includes a clock signal source which produces a clock signal, a buffer circuit which drives the clock signal while adjusting rise and fall times of the clock signal according to control signals, a rise-time frequency generator, responsive to the control signals, which produces a rise-time signal having a frequency corresponding to the rise time given by the buffer circuit, a fall-time frequency generator, responsive to the control signals, which produces a fall-time signal having a frequency corresponding to the fall time given by the buffer circuit, and a control signal generator which produces the control signals, based on the frequencies of the rise-time signal and fall-time signal.

Abstract: In a frequency dividing device, a 1/P frequency divider subjects an input clock signal to 1/P frequency division. A phase shifter shifts the phase of the 1/P frequency signal and outputs multiple different Q-phase signals. A switch controls phase shifting in accordance with a division ratio control signal, to switch the Q-phase signals from one to another. A 1/R frequency divider subjects the output from the switch to 1/R frequency division and outputs an Rth frequency clock signal. A ½ frequency divider subjects the Rth frequency clock signal to ½ frequency division and outputs a frequency divided clock signal. A division ratio setter receives a division ratio set signal and generates the division ratio control signal. As a division ratio, P×R×2?2×P/Q, P×R×2?P/Q, P×R×2, P×R×2+P/Q, and P×R×2+2×P/Q can be set.

Abstract: A phase difference detector for detecting a phase difference between input clocks which both have a same first frequency, including: a pulse width conversion unit for converting the input clocks into a phase difference signal indicating by a pulse width a phase difference between the input clocks; and a counter unit which samples a level of the phase difference signal using a reference clock having a second frequency which is slower than the first frequency, and counts the number of levels of the phase difference signal using a first weighting according to the sampled level of the phase difference signal. When the count value of the counter unit transits in a predetermined range, the phase difference between the input clocks is detected according to the first weighting.

Abstract: A latch circuit includes a voltage driven type data reading unit and a voltage driven type data holding unit, and operates based on a clock signal that is supplied from an outside source. The data reading unit reads both a first input data and a second input data, and outputs both a first output data and a second output data based on both the first input data and the second input data, while the data holding unit holds both the first output data and the second output data. Both the first input data and the second input data are differential signals, and both the first output data and the second output data are differential signals that have phases that are inverted.

Abstract: A clock selection circuit and synthesizer that is capable of selecting an optimum clock signal from among a plurality of clock signals in a short time. A reference-clock counter counts clock pulses in an inputted reference clock signal (REF). A clock counter counts clock pulses in one of the plurality of clock signals which is selected by a selection unit and frequency-divided by a frequency divider. An instruction-signal output unit outputs a plurality of comparison-instruction signals during an interval in which a difference occurs between the counts of two of the plurality of clock signals having the closest frequencies. A comparison unit compares the count of the reference-clock counter and the count of the clock counter. The selection unit selects a clock signal by a binary search according to the result of the comparison.

Abstract: An optical dispersion monitoring apparatus and an optical dispersion monitoring method are capable of monitoring dispersion accurately with a simple construction in an optical transmission system using the same. To this end, the optical dispersion monitoring apparatus includes a light receiving section converting an input optical signal into an electrical signal, a signal transition position detecting section detecting the voltage level of a waveform of the output signal from the light receiving section, at a crossing point of a rising edge and a falling edge, and a cumulative dispersion information extracting section comparing the voltage level at the crossing point with a reference signal to extracts cumulative dispersion information.

Abstract: A clock frequency divider is provided which has first through Pth (where P is an integer) sub-counters, each capable of counting M+1 clock pulses and provided in parallel, and first through Pth clock signals are provided to the sub-counters, which has same period as a reference clock signal and are sequentially shifted by 1/P of the period of the reference clock signal. Of the first through Pth sub-counters, when the Nth sub-counter (where N is an arbitrary number from 1 to P) finishes counting a prescribed number M of reference clock pulses, all the other sub-counters are initialized, or, at least the (N+1)th sub-counter is initialized.

Abstract: A latch circuit includes a voltage driven type data reading unit and a voltage driven type data holding unit, and operates based on a clock signal that is supplied from an outside source. The data reading unit reads both a first input data and a second input data, and outputs both a first output data and a second output data based on both the first input data and the second input data, while the data holding unit holds both the first output data and the second output data. Both the first input data and the second input data are differential signals, and both the first output data and the second output data are differential signals that have phases that are inverted.

Abstract: According to a PLL circuit of the present invention, an output of a phase comparator is adjusted according to a space-to-mark transition-probability of an input signal so that an output of a voltage controlled oscillator has a predetermined frequency and phase. Therefore, even when a phase of a timing clock is set other than at 0, an output of the PLL circuit can be kept at the set phase, irrespective of the space-to-mark transition-probability. By using the PLL circuit as such in an optical communication apparatus and an optical communication system, a discrimination point can be kept almost fixed, and therefore, it is possible to lower an error rate.

Abstract: A clock frequency divider is provided which has first through Pth (where P is an integer) sub-counters, each capable of counting M+1 clock pulses and provided in parallel, and first through Pth clock signals are provided to the sub-counters, which has same period as a reference clock signal and are sequentially shifted by 1/P of the period of the reference clock signal. Of the first through Pth sub-counters, when the Nth sub-counter (where N is an arbitrary number from 1 to P) finishes counting a prescribed number M of reference clock pulses, all the other sub-counters are initialized, or, at least the (N+1)th sub-counter is initialized.

Abstract: The present invention provides a demodulation device including: a synthesizer generating a local signal; and a mixer mixing an input signal, which is modulated by a carrier frequency, with the local signal to output an intermediate frequency signal whose carrier has an intermediate frequency. An intermediate frequency setting unit sets one of a plurality of intermediate frequencies, and a demodulator extracts and reproduces an intermediate frequency signal at the set intermediate frequency.

Abstract: An object of the invention is to provide an optical dispersion monitoring apparatus and an optical dispersion monitoring method, capable of monitoring dispersion accurately with a simple construction, and to an optical transmission system using the same. To this end, the optical dispersion monitoring apparatus comprises: a light receiving section converting an input optical signal into an electrical signal, a signal transition position detecting section detecting the voltage level of a waveform of the output signal from the light receiving section, at a crossing point of a rising edge and a failing edge, and a cumulative dispersion information extracting section comparing the voltage level at the crossing point with a reference signal to extracts cumulative dispersion information.

Abstract: According to a PLL circuit of the present invention, an output of a phase comparator is adjusted according to a space-to-mark transition-probability of an input signal so that an output of a voltage controlled oscillator has a predetermined frequency and phase. Therefore, even when a phase of a timing clock is set other than at 0, an output of the PLL circuit can be kept at the set phase, irrespective of the space-to-mark transition-probability. By using the PLL circuit as such in an optical communication apparatus and an optical communication system, a discrimination point can be kept almost fixed, and therefore, it is possible to lower an error rate.