Abstract: Circuits, systems, and methods are described herein for generating master clock signals and slave clock signals for controlling a flip-flop having a master latch and a slave latch. A circuit includes a master latch configured to latch an input data signal and to output a data latch signal based on a master clock signal. The circuit also includes a slave latch coupled to the master latch and configured to generate an output data signal based on a slave latch clock signal and the data latch signal. Additionally, the circuit includes a skewed clock circuit coupled to the master latch and the slave latch. The skewed clock circuit is configured to receive a clock signal and generate the master clock signal and the slave clock signal based on the clock signal. The master clock signal and the slave clock signal are independent clock signals whose timing is skewed relative to one another by the skewed clock circuit.

Abstract: An electrical circuit and method for de-modulation and carrier recovery of PSK modulated carrier signals in analog domain are described. A portion of the received PSK-modulated carrier signal is passed through a signal multiplication circuit to obtain a frequency-multiplied carrier that is absent of the PSK modulation, which is then passed through a frequency dividing circuit to obtain a reference carrier at the received carrier frequency. The reference signal is then mixed with the received PSK-modulated carrier signal to obtain a de-modulated baseband signal. The method may be used in heterodyne receivers of optical BPSK and QPSK signals.

Abstract: An electrical circuit and method for de-modulation and carrier recovery of PSK modulated carrier signals in analog domain are described. A portion of the received PSK-modulated carrier signal is passed through a signal multiplication circuit to obtain a frequency-multiplied carrier that is absent of the PSK modulation, which is then passed through a frequency dividing circuit to obtain a reference carrier at the received carrier frequency. The reference signal is then mixed with the received PSK-modulated carrier signal to obtain a de-modulated baseband signal. The method may be used in heterodyne receivers of optical BPSK and QPSK signals.

Abstract: A frequency-to-voltage (F2V) conversion module includes a pulse shaping module that generates a square wave signal based on an oscillator signal, an edge to pulse conversion module that generates a pulse train based on corresponding rising and falling edges of the square wave signal, and an integrator module that generates an output voltage based on the pulse train. The output voltage is based on a frequency of the oscillator signal.

Abstract: The frequency decision device determines frequency of the measured rectangular signal by simple and easy means. The frequency decision device inputs the measured rectangular signal that frequency (or period) changes dynamically. It generates a rectangular reference signal of predetermined on width ? synchronizing to the edge based on a positive going edge of this measured rectangle signal. And it watches the order of measured rectangle signal and falling edges of the rectangular reference signal. When this sequential order reversed, it detects that length of the ON time of ON time of the measured rectangle signal and the measured rectangular signal reversed.

Abstract: A system for monitoring a clock input signal including a reference clock to be monitored, a flip-flop, a plurality of delay logic blocks, a sampling unit, and a comparison unit. The reference clock may have an expected maximum frequency. The flip-flop may be configured to generate a corresponding clock signal at a reduced frequency compared to the reference clock. The plurality of delay logic blocks may be configured to receive the reduced frequency clock signal and delay the signal for various amounts of time, each less than an expected period of the reference clock. The sampling unit may be configured to sample the signals output from the plurality of delay logic blocks. The comparison unit may be configured to receive the outputs of the flip-flop and the sampling unit and use these outputs to determine if the reference clock is running at an acceptable frequency compared to the expected frequency.

Abstract: An electronic safety device for a protection barrier includes a transponder, a transceiver device for receiving a return signal from the transponder, the transponder being movable with respect to the transceiver and adapted to be placed at a current distance, an electric circuit which is switched when the distance is lower or higher than a reference distance and a control and switching system. The transceiver device processes the return signal to generate a control signal with an electric parameter variable in function of the distance. The control signal is a periodic signal with a frequency and has a first spectrum with a middle interval and a second spectrum with lateral intervals shifted with respect the middle interval when the distance is higher than the reference distance, the parameter being associated to a frequency value that comprises either into the middle interval or into one of the lateral intervals.

Abstract: A calibrated crystal warm-up method that can include determining the number of clock cycles of a crystal clock reference signal from a crystal oscillator occur during a single clock cycle of a low-power oscillator. Further, the determination can occur when the crystal oscillator is warmed up. The method can also include comparing a number of clock cycles of the crystal clock reference signal with a previously determined number of clock cycles of the crystal clock reference signal to indicate whether the crystal oscillator is warmed up. Further, the method can include counting the number of clock cycles of a low-power clock reference signal have occurred up until the time it has been determined that the crystal oscillator has been warmed up.

Abstract: An all-digital frequency detector is provided, which includes a phase-frequency detector receiving a reference clock and an input clock, two sample/hold circuits sampling the phase-frequency detector outputs responsive to a ninety-degree phase shifted reference clock and a ninety-degree phase shifted input clock, a plurality of logical operators to generate an output frequency detection signal and a output clock responsive to the difference between the reference clock and the input clock.

Abstract: A circuit, set forth by way of example and not limitation, includes a signal detector operative to detect two types of signals, where the two types of signals include a higher-frequency signal and a lower-frequency signal. The signal detector is operative to detect that a received input signal is one of the two types of signals. An output driver is operative to receive the input signal and to adjust conditioning performed on the input signal to create an output signal for transmission over a communication channel, where the adjustment is based on the detection by the signal detector.

Abstract: In a particular embodiment, a digital circuit includes a frequency detection circuit operative to compare information related to transitions between sequential samples of a received signal. The frequency detection circuit is further operative to generate a control signal to reduce a sampling rate of the received signal in response to a predetermined number of the sequential samples having a same value. The digital circuit also includes a digital phase detector operative to provide the information related to the transitions between sequential samples to the frequency detection circuit.

Abstract: A frequency measuring apparatus includes: a counter section adapted to count a signal including a pulse signal for a predetermined time period, and output a binary count value corresponding to a frequency of the signal including the pulse signal; and a low pass filter section adapted to perform a filtering process on the count value, wherein the low pass filter section includes a first stage filter and a second stage filter, the first stage filter is a moving average filter to which the count value is input, and which provides a binary output with a high-frequency component reduced, and the second stage filter performs an average value calculation on the binary output to provide an output with the high-frequency component reduced.

Abstract: A phase frequency detector circuit includes an edge detector circuit, a plurality of phase frequency detector sub-circuits, and a decision circuit. The edge detector circuit is configured to receive a first input signal and a second input signal. The decision circuit is configured to detect whether a blind condition exits based on outputs of the edge detector circuit and outputs of the plurality of phase frequency detector sub-circuits. Responsive to a result of the decision circuit, a corresponding frequency detector sub-circuit of the plurality of phase frequency detector sub-circuit is configured to provide signals for use in determining a phase difference between the first input signal and the second input signal.

Abstract: A frequency measuring apparatus includes: a counter section adapted to count a signal including a pulse signal for a predetermined time period, and output a binary count value corresponding to a frequency of the signal including the pulse signal; and a low pass filter section adapted to perform a filtering process on the count value, wherein the low pass filter section includes a first stage filter and a second stage filter, the first stage filter is a moving average filter to which the count value is input, and which provides a binary output with a high-frequency component reduced, and the second stage filter performs an average value calculation on the binary output to provide an output with the high-frequency component reduced.

Abstract: A frequency measurement device for measuring a frequency of a signal to be measured including a pulse signal, includes: a signal multiplier section that multiplies the signal to be measured by n (n is an integer) and outputs a multiplied signal; a counter section that counts the multiplied signal with a predetermined gate time and outputs a count value of the frequency of the signal to be measured at a predetermined period; and a low-pass filter that outputs a signal corresponding to the frequency of the signal to be measured based on the count value outputted at the predetermined period.

Abstract: A frequency measuring apparatus includes: a high-order digit calculation section adapted to measure an input signal and output a high-order digit value of a frequency value of the input signal; a low-order digit calculation section adapted to measure the input signal and output a low-order digit value of the frequency value of the input signal; and an adding section adapted to add the high-order digit value and the low-order digit value to each other to output the frequency value of the input signal.

Abstract: The phase-frequency detector (PFD) includes a frequency detector (FD) arranged to receive orthogonal signal pairs of a reference signal and a feedback signal and estimate a frequency error between a reference signal and a feedback signal; a FD voltage-to-current converter arranged to convert the frequency error into a first current; a phase detector (PD) arranged to receive the orthogonal signal pairs and estimate a phase error between the reference signal and the feedback signal, and a PD voltage-to-current converter arranged to convert the phase error into a second current.

Abstract: In a particular embodiment, a digital circuit includes a frequency detection circuit operative to compare information related to transitions between sequential samples of a received signal. The frequency detection circuit is further operative to generate a control signal to reduce a sampling rate of the received signal in response to a predetermined number of the sequential samples having a same value. The digital circuit also includes a digital phase detector operative to provide the information related to the transitions between sequential samples to the frequency detection circuit.

Abstract: Provided are a lock detection circuit and a lock detecting method. The lock detection circuit includes two delay devices, four flip-flops and two logic gates, and can accurately detect a lock state of a phase locked loop (PLL) circuit. Therefore, the lock detection circuit can be implemented in a simple structure, and as a result, the lock detection circuit can be compact in size and can consume less electric power. Also, the lock detecting method enables lock detection process to be simpler, so that a lock state can be detected within a short time period.

Abstract: A window sampling system and method are provided for comparing a signal with an unknown frequency to a reference clock. A pattern modulator accepts a compClk signal and supplies a test window with a period equal to n compClk periods, where n is an integer greater than 1. A pattern detector accepts the test window and a reference clock, and contrasts the test window with the reference clock. In response to failing to fit n reference clock periods inside the test window, the pattern detector supplies a frequency pattern detector output signal (fpdOut) indicating that the frequency of the compClk is greater than the reference clock frequency.

Abstract: A circuit is described that detects high and low frequencies and additional clock frequencies and outputs a signal that indicates a high, a low frequency or an additional mode. When in the low frequency low frequency mode signals are regenerated free of any high frequency signals from appearing on the filtered low frequency clock line. The rising and falling edges of the input clock are low pass filtered separately and then combined to generate a low frequency clock or the additional input clock and that retains the input clock pulse width and duty cycle.

Abstract: A clock circuit includes a phase-lock loop for generating an output clock signal based on a data signal and a harmonic frequency detector for detecting whether the frequency of the output clock signal is a harmonic frequency of a frequency of a reference clock signal. The harmonic frequency detector includes a counter for generating a first divided clock signal by dividing the frequency of the output clock signal by a first divisor. Additionally, the harmonic frequency detector includes a counter for generating a second divided clock signal by dividing the frequency of the reference clock signal by a second divisor. The harmonic frequency detector also includes a frequency comparator for generating an output indicating whether the frequency of the output clock signal is a harmonic frequency of the frequency of the reference clock signal based on the first divided clock signal and the second divided clock signal.

Abstract: A frequency detection circuit and a detection method thereof suitable for a clock data recovery (CDR) circuit are provided. The frequency detection circuit includes a phase detector, a first delayer, a frequency detector, and a logic circuit. The phase detector samples a data signal according to a first clock signal provided by the CDR circuit and provides a phase instruction signal according to the sampling. The first delayer delays the first clock signal to obtain a second clock signal. The frequency detector samples the data signal according to the second clock signal and provides a frequency instruction signal according to the sampling. The logic circuit generates a clock instruction signal according to the phase instruction signal and the frequency instruction signal. The CDR circuit adjusts the frequency of the first clock signal according to the status of the clock instruction signal.

Abstract: Disclosed is a PLL circuit including a phase frequency detector (PFD) for comparing phase and frequency between an input signal and an output signal, a charge pump circuit for charging a capacitor when an up-signal from the PFD is activated, discharging the capacitor when a down-signal is activated, and for outputting the terminal voltage of the capacitor as a control voltage, and a VCO for outputting an output signal of a frequency in accordance with the control voltage. An output of the VCO is fed back as an output signal to the PFD as input. The PFD includes a delay adjustment circuit for exercising control for resetting the up-signal and the down-signal with a preset delay as from a time point both up-signal and the down-signal have been activated. There is also provided a comparator amplifier circuit for comparing a reference voltage, corresponding to a control voltage when both up-signal and down-signal are activated, to supply first and second control signals to the delay adjustment circuit.

Abstract: A digital circuit is disclosed for detecting clock activity in an integrated circuit (IC) device. In one implementation, a clock detection circuit can include two flip flops. A first flip flop detects activity on the clock being tested (e.g., the flip flop is set when a positive clock edge is detected). A second flip flop is coupled to the output of first flip flop and is operable by an enable signal to sample the output of the first flip flop. The output of the second flip flop is asserted as active, when a positive clock edge occurs between the release of the reset signal on the first flip flop and the assertion of the enable signal on the second flip flop. In some implementations, one or more additional flips can be interposed between the first and second flips to control metastability.

Abstract: Disclosed is a high-frequency signal detector circuit including a diode detector circuit for detecting an input signal by diode detection; a differential-input/differential output amplifier with a common mode feedback circuit, the amplifier including a differential amplifying circuit for differentially receiving outputs of the diode detector circuit and outputting a differential output signal, and a common mode feedback circuit for controlling the differential amplifying circuit in such a manner that a voltage corresponding to a mid-point of the differential output signal from the differential amplifying circuit will take on a voltage identical with a prescribed voltage; and a differential-input/single-ended output amplifier for receiving the differential output signal of the differential amplifying circuit and outputting a single-ended output signal.

Abstract: A stream of data may flow over a fiber or other medium without any accompanying clock signal. The receiving device may then be required to process this data synchronously. Embodiments describe clock and data recovery (CDR) circuits which may sample a data signal at a plurality of sampling points to partition a clock cycle into four phase regions P1, P2, P3, and P4 which may be represented on a phase plane being divided into four quadrants. A relative phase between a data signal transition edge and a clock phase may be represented by a phasor on the phase plane. The clock phase and frequency may be adjusted by determining the instantaneous location of the phasor and the direction of phasor rotation in the phase plane.

Abstract: Methods and apparatus nullify an intrinsic jitter component in a digital clock recovery circuit induced by a time base frequency difference between an incoming data signal and a local synchronization clock for the digital clock recovery circuit. The techniques disclosed herein permit a recovered clock signal to be digitally filtered and applied to the digital clock recovery circuit clock synthesis unit (CSU) as a synchronization reference clock signal, which advantageously eliminates a time base frequency difference to reduce that jitter component and also reduces an intrinsic jitter component associated with jitter already present in the incoming data signal. In one embodiment, a state machine uses a filtered version of a recovered clock signal as a reference when the frequency of the filtered version of the recovered clock signal is relatively close to the frequency of the CSU reference clock signal.

Abstract: A frequency sensor includes at least one a resistor element and a capacitor. A frequency is detected according to a charging/discharging time to/from the capacitor, thereby realizing a frequency sensor with reduced power consumption and reduced circuit scale. Further, plural resistors and plural capacitors can be provided, along with switches connected to the respective resistors and capacitors. Additionally, a time constant can be adjusted after production, whereby variations in production can be reduced. Furthermore, a self-diagnosis circuit can be included for determining whether the frequency sensor itself operates normally or not. Thus, a highly-reliable frequency sensor can be realized.

Abstract: The circuit for detecting the maximal frequency of the pulse frequency modulation includes an oscillator-controlling unit, a delay circuit and a master-slave register. The oscillator-controlling unit is connected to an oscillator, which generates the pulse frequency modulation signals, and includes a first-half pulse-generating module and a second-half pulse-generating module. The delay circuit is connected to the second-half pulse-generating module. The master-slave register includes a clock, an input end and an output end, wherein the input end is connected to the oscillator-controlling unit, and the clock is connected to the delay circuit.

Abstract: The invention concerns counting circuitry for providing a corrected count value based on the number of rising and falling edges of an input signal occurring during a reference time period, the counting circuitry comprising a counter (22) arranged to provide a first count value based on one of the number of said rising edges of said input signal occurring during said reference time period, and the number of said falling edges of said input signal occurring during said reference time period; characterized in that said counting circuitry further comprises adjustment circuitry (24-26) arranged to generate a corrected count value by determining the state of said input signal at the start time (70) and end time (72) of said reference time period, and adjusting said first count value if the state of said input signal at the start of said reference time period is different from the state of said input signal at the end of said reference time period.

Abstract: The present invention discloses a frequency detecting apparatus for detecting a frequency of an input clock. The frequency detecting apparatus includes: a pulse generator, a digital signal generator, and a decoder. The pulse generator is coupled to the input clock for extracting a period of the input clock to generate a pulse, and the digital signal generator is coupled to the pulse generator for converting the pulse into a plurality of logic values. The digital signal generator includes: a delay module coupled to the pulse, for delaying the pulse to generate a plurality of delayed pulses according to a plurality of delay amounts, respectively; and a sampling module coupled to the delay module for sampling the pulse to generate the logic values according to the delayed pulses, respectively. The decoder is coupled to the digital signal generator for determining the frequency of the input clock according to the logic values.

Abstract: The present invention discloses a frequency detecting apparatus for detecting a frequency of an input clock. The frequency detecting apparatus includes: a pulse generator, a digital signal generator, and a decoder. The pulse generator is coupled to the input clock for extracting a period of the input clock to generate a pulse, and the digital signal generator is coupled to the pulse generator for converting the pulse into a plurality of logic values The digital signal generator includes: a delay module coupled to the pulse, for delaying the pulse to generate a plurality of delayed pulses according to a plurality of delay amounts, respectively; and a sampling module coupled to the delay module for sampling the pulse to generate the logic values according to the delayed pulses, respectively. The decoder is coupled to the digital signal generator for determining the frequency of the input clock according to the logic values.

Abstract: The phase-frequency detector may include a first flip-flop configured to generate a first signal, the first signal transitioning to a first logic level in response to a first edge of a first input signal and transitioning to a second logic level in response to a delayed reset signal and a second flip-flop configured to generate a second signal, the second signal transitioning to the first logic level in response to a second edge of a second input signal and transitioning to the second logic level in response to the delayed reset signal. The phase-frequency detector may further include a first delay unit configured to delay a reset signal to generate the delayed reset signal and a second delay unit configured to delay the reset signal to generate an output control signal for adjusting at least one of the first and second signals.

Abstract: A delayed lock loop for preventing a stuck fail in a dead-zone includes a clock buffering block for generating a first and a second internal clock signals; a phase comparison block for delaying a feedback signal by a first predetermined value and for respectively comparing a phase of a delayed feedback signal and a phase of the feedback signal with a phase of the external clock signal; a clock selecting block for selecting one of the first and second internal clock signals based on one comparison result to thereby generate a selected internal clock signal; a stuck checking block for determining a delay value based on the other comparison result; a delay line block for delaying the selected internal clock signal by the delay value; and an output buffer for buffering an outputted signal from the delay line block to thereby generating a DLL clock signal.

Abstract: A charge pump clock circuit for a memory device generates pump clock signals at an adaptive rate. Clock edges are generated at a minimum of TD seconds apart so long as address transitions do not exceed a pre-determined limit. However, if address changes are occurring more frequently than this limit, i.e., 1/(2*TD), then clock edges will be generated at a rate that is proportional to the rate of address changes, where TD is approximately half of the address period. Two logic rules are implemented in hardware or equivalent software to make the clock signal adjustments.

Abstract: A device such as a programmable logic device (“PLD”) includes circuitry for detecting the PPM frequency difference between two input clock signals. For example, this circuitry may accept a user-programmable PPM threshold value and output a signal when this threshold value is met.

Abstract: A frequency detection circuit and method of detecting the frequency of a clock signal, and a latency signal generation circuit for a semiconductor memory device that includes the frequency detection circuit. The frequency detection circuit includes a frequency detector and an output controller, which determines whether or not the frequency of the clock signal is higher than a predetermined value. Embodiments of the invention have an increased accuracy, increased efficiency, and a reduced current consumption over conventional art.

Abstract: A system and method that can be utilized to implement voltage adjustment (e.g., for an integrated circuit). In one embodiment, the system comprises a frequency generator that provides a clock signal having a frequency that varies based on an operating voltage. The system also includes a controller that provides a control signal to adjust the operating voltage based on adjustments to the frequency of the clock signal.

Abstract: An improved coarse frequency detector includes a first storage device responsive to a data signal and a sub-multiple of a clock signal for detecting a first transition in the data signal during a predetermined state of the sub-multiple of the clock signal and generating an intermediate signal, and a second storage device responsive to the data signal and the intermediate signal for detecting a second transition in the data signal having the same polarity as the first transition during the predetermined state of the sub-multiple of the clock signal and generating an up-pulse.

Abstract: A delay-lock loop includes several delay lines, all but the first of which is composed of at least one variable delay unit that provides a fixed delay and a variable delay. The first delay line is composed of a plurality of fixed delay units, but no variable delay units. The remaining delay lines are each composed of different numbers of variable delay units to provide respective clock signals having different phases, but they do not include any of the fixed delay units. The first and a last delay line receive an input clock signal. Each of the remaining delay lines are coupled to an output of one of the fixed delay units depending on the number of variable delay units in the delay line so that the resulting clock signals have all been delayed the same number of fixed delay periods.

Abstract: A phase-locked loop circuit has a fractional-frequency-interval phase frequency detector, a charge pump, an oscillator, and a divider. The fractional-frequency-interval phase frequency detector has a phase frequency detector unit that is utilized as or comprises a plurality of phase frequency detector units. The divider is responsive to the oscillator and provides divider values for dividing an oscillator frequency by the divider values to provide a feedback frequency of a feedback loop signal of the phase-locked loop circuit. A reference input frequency is input as a first input into the phase frequency detector unit. The feedback frequency is input and selectively delayed as second inputs into the phase frequency detector unit so that the second inputs are aligned for input according to the reference input frequency and an oscillator frequency is, in effect, responsive to the phase frequency detector units and allowed to be divided by a fractional-integer divider value.

Abstract: The present invention relates to a device for comparison CMP, which is designed to emit a control signal Vcnt, which is representative of a difference which exists between the input signal frequencies Vdiv and Vref. The device according to the invention includes a phase/frequency comparator PD, which supplies a regulation signal Tun, which is subjected to pulse width modulation according to the difference observed. The device also includes a current source, which is designed to emit a charge current Ics, with a value which is controlled by the regulation signal Tun. The device further includes a capacitive element Cs, which is designed to generate the control signal Vcnt, under the effect of the charge current Ics. By means of a regulation signal Tun, which has a frequency which is virtually constant, the invention makes it possible to impose high-frequency variations on the control signal Vcnt.

Abstract: A PLL lock generator using one circuit (lock detection block) to indicate whether an output clock signal is locked to an input reference signal, and another circuit to determine whether the signals are out-of-lock. A lock generation blocks examines several indications of lock detection before generating a lock signal. Short term fluctuations (such as jitter) in lock and out-of-lock indications may be ignored. An embodiment of lock detection block contains a first flip-flop latching an up signal and clocked by a down signal, and a second flip-flip latching the down signal and clocked by an up signal. The up and down signals may be generated by a phase frequency detector. An examination circuit examines the output of lock detection block to generate the lock indications.

Abstract: A latch for detecting a state transition of an input signal and generating a self-clearing reset signal on an output. The latch comprises: 1) a transfer gate for passing the input signal to a first node when the input transfer gate is enabled; 2) a transition detector for detecting a transition of the first node from a first to a second state, wherein the transition detector, in response to the transition, disables the transfer gate and enables the reset signal; and 3) a feedback loop circuit for detecting enabling of the reset signal. The feedback loop circuit, in response to the enabling, changes the first node from the second state back to the first state. The transition detector, in response to the changing of the first node back to the first state, disables the reset signal.

Abstract: A frequency comparator circuit is configured to compare whether the frequency of two input signals are within a tolerance of each other. The frequency comparator circuit includes two counter circuits, an AND gate, and a frequency detector circuit that is configured to provide two reset signals. The two counter circuits are arranged to be clocked by a respective one of the two input signals, and further arranged to be reset by a respective one of the two reset signals. Further, the AND gate is arranged to perform an AND function on the overflow outputs of the first and second counter circuits to provide an status signal. If the status signal is high, the difference in frequency between the two input signals is less than the tolerance. If the status signal is low, the difference in frequency between the two input signals exceeds the tolerance.

Abstract: A phase frequency detector with a narrow control pulse comprises mainly two substantially equivalent phase latches with a narrow control pulse, and a reset signal generating unit. Each phase latch of a narrow control pulse has a clock pulse input end and a signal output end. Both latches also are connected to the reset signal generating unit. The logic value of each signal output end is decided by which clock pulse input appears first. The reset signal generating unit decides whether or not to generate a reset signal according to the logic values of both signal output ends. The reset signal is then sent to both phase latches of a narrow control pulse, if generated. The present invention can be implemented by a simple circuit. Comparing with the RS NAND PFD or master-slave D PFD, the PFD of the invention has the advantages of faster speed, saving more power and smaller IC chip area.

Abstract: A latch for detecting a state transition of an input signal and generating a self-clearing reset signal on an output. The latch comprises: 1) a transfer gate for passing the input signal to a first node when the input transfer gate is enabled; 2) a transition detector for detecting a transition of the first node from a first to a second state, wherein the transition detector, in response to the transition, disables the transfer gate and enables the reset signal; and 3) a feedback loop circuit for detecting enabling of the reset signal. The feedback loop circuit, in response to the enabling, changes the first node from the second state back to the first state. The transition detector, in response to the changing of the first node back to the first state, disables the reset signal.

Abstract: A digital frequency comparator includes two double-edge triggered flip-flops and a combination logic. Each of the double-edge triggered flip-flops includes two D-type flip-flops and two multiplexers. The first D-type flip-flop receives a first reference clock pulse and is triggered by a data signal. The second D-type flip-flop receives the first reference clock pulse and is triggered by the reverse of the data signal. The first multiplexer provides the output of the first D-type flip-flop when the data signal is 1 and the output of the second D-type flip-flop when the data signal is 0. The second multiplexer provides the output of the first D-type flip-flop when the data signal is 0 and the output of the second D-type flip-flop when the data signal is 1. The combination logic enables an UP pulse when the data signal transmission clock is faster in frequency than the first reference clock signal.

Abstract: A system 400 and method 1400 are disclosed for a lock detection circuit of a phase locked loop used in a communications device. The lock detection circuit includes a cycle slip detector and a clock presence detector. The cycle slip detector receives a reference clock and a VCO feedback clock, and in response to the frequency difference between the reference clock and the VCO feedback clock that remains for a time period greater than the inverse of the frequency difference of the clocks, generates a no cycle slips alarm indication. The no cycle slips alarm status enables the lock detection circuit to provide an indication to the PLL, of the lock condition and whether a cycle slip has occurred. The clock presence detector receives the reference clock and the VCO feedback clock, and in response to determining whether the reference clock or the VCO feedback clock is missing for a time greater than a predetermined count of either remaining clock, generate a no VCO alarm and a no REF alarm indication.