Abstract: Phase-locked loop (PLL) circuitry in which a sampling phase detector samples the output signal in accordance with the reference signal and a frequency detector detects the output signal frequency in accordance with the reference signal.

Abstract: A clock and data recovery circuit comprising a phase detection circuit, first and second oscillators, and a flip-flop. The phase detection circuit outputs a detection signal according to a significant transition of an input signal. Each oscillator receives the detection signal and operates alternately in a clock and data recovery mode and a phase-locked mode. When the first oscillator operates in the clock and data recovery mode and outputs a first clock to control the flip-flop to output an output signal, the second oscillator operates in the phase-locked mode to adjust a frequency of a second clock. Before switching to the clock and data recovery mode, the second oscillator synchronizes the second clock with the first clock.

Abstract: The phase locked loop (PLL) with adjustable phase shift is described. The PLL includes a voltage controlled oscillator which is capable of generating multiple phase shifted output signals, and multiple phase detectors capable of determining the phase differences between the output signals and a reference clock. The PLL further includes a weighting device capable of weighting the phase differences and generating a control signal for the voltage controlled oscillator.

Abstract: A phase locked loop has a digitally controlled oscillator (DCO) for generating a DCO output signal (fOSC), a clock divider coupled to the DCO and receiving the DCO output signal and outputting a feedback clock signal (fN), and a phase frequency detector (PFD) coupled to the DCO and controlling the DCO by a DCO control signal (dCNTL).

Abstract: A method and system for determining the eye pattern margin parameters of a receiver system during diagnostic testing is presented. The circuitry in the receiver's front end comprises a series of latches, XOR gates and OR gates which first provide the data samples and edge samples, i.e., data sampled at the rising or falling edge of an (edge) clock characterized by a phase delay relative to the data sampling clock. The receiver also comprises optimization circuitry for the ideal alignment of the edge clock (edges) with the data edges. The method further provides for a phase shifting of the edge clock to the left and right from the ideal/locked position to screen the data eye pattern in order to compute the Bit Error Rate (BER) value. The position of the edge clock relative to the data sampling clock determines the horizontal eye opening for the computed BER.

Abstract: A receive circuit for receiving a signal transmitted via an electric signal conductor. A first sampling circuit generates a first sample value that indicates whether the signal exceeds a first threshold level, and a second sampling circuit generates a second sample value that indicates whether the signal exceeds a second threshold level. A first select circuit receives the first and second sample values from the first and second sampling circuits and selects, according to a previously generated sample value, either the first sample value or the second sample value to be output as a selected sample value.

Abstract: The control word input to a Digitally Controlled Oscillator (DCO) is modified to reduce non-monotonic regions in the output response of the DCO. The DCO may be included in a Phase-Locked Loop (PLL) circuit for generating an output signal that locks onto either the phase or frequency of a reference signal input. By modifying the control word input to the DCO to avoid non-monotonic regions in the DCO output response, PLL phase noise is reduced. In one embodiment, the control word is modified by reordering or skipping control word values input to the DCO that correspond to non-monotonic regions in the output response of the DCO circuit.

Abstract: A clock and data recovery circuit that tracks the frequency and phase fluctuation of serial data includes a feedback controller for monitoring tracking speed of an extraction clock with respect to the frequency and phase fluctuation of the serial data and applying feedback control to an integrator adaptively and moment to moment, thereby raising the tracking speed of the recovered clock and improving the jitter tolerance characteristic.

Abstract: A dual path loop filter circuit for a phase lock loop is described. The filter circuit allows the filter to be integrated into a phase lock loop IC circuit without using active circuit components that may create additional noise and consume additional power. The filter circuit structure allows for a low capacitance capacitor to be used to filter out any undesired signals.

Abstract: A two-point frequency modulation apparatus is proposed whereby the spectrum of transmission waves is kept within the spectrum mask. Voltage is supplied to the control voltage terminal of VCO 1 in accordance with modulation data via noise shaper 101 that has operating characteristics of attenuating more noise at higher frequencies. As a result, by virtue of the working of noise shaper 101, the signal level outputted from the PLL circuit combining the modulation signal and the quantization noise decreases in proportion to the distance form the central frequency, so that two-point frequency modulation apparatus 100 is made possible whereby the spectrum of an RF modulation signal is kept within the spectrum mask.

Abstract: A novel and useful fast hopping frequency synthesizer and transmitter associated therewith. The frequency synthesizer and transmitter incorporates a digitally controlled oscillator (DCO) adapted to operate open loop. Instantaneous frequency switching is achieved by changing an oscillator tuning word (OTW) to imitate the three oscillators of a UWB transmitter. In one embodiment, the DCO can change the frequency instantaneously within the 1/fT of the varactor devices used to construct the DCO. An all digital phase lock loop (ADPLL) is used for offline calibration prior to the start of packet transmission or reception. Any phase shift during the switching is tracked by a digital circuit in the transmitter. In a second embodiment, additional frequency accuracy is provided by use of a numerically controlled oscillator (NCO) that functions to generate a fine resolution complex exponential waveform which effectively shifts the synthesized frequency.

Abstract: A method and apparatus for recovering data by a digital audio interface begins by receiving a stream of biphase encoded data. The processing continues by determining whether a next transition of a frame of the plurality of frames occurs during a first, second, or third time window after a preceding transition of the frame. When the next transition occurs during the second predetermined time, the digital audio interface synchronizes to a data rate of the stream of biphase encoded data based on the next transition and the preceding transition. If, the next transition occurs during the first or third predetermined windows, the digital audio interface synchronizes to a data rate of the stream of biphase encoded data based on the preceding transition edge and a subsequent transition. When the transition occurs during the third time window, the biphase encoding is violated, which indicates that a preamble is being received.

Abstract: A quarter-rate phase detector can include: four latches controllable to latch, at different times according to quadrature clock signals, respectively, data received by the phase detector so as to form latched signals; an error circuit to combine corresponding ones of the latched signals, respectively, resulting in a plurality of intermediate signals; and a multiplexing unit to selectively output the intermediate signals as a phase error signal. A related method can have similar features.

Abstract: A phase measurement system for measuring phase between an input signal having a frequency and a reference signal having a substantially different frequency includes: a phase comparator having an output representing a time between a crossing of a first threshold by a clock derived from the reference signal and a predetermined time along an interval from a first sample to a second sample, where the input signal crosses a second threshold on the interval; an interpolator having an output indicative of an interpolated time of the second-threshold-crossing on the interval in the input signal; and a phase calculator which computes the phase difference by combining the phase comparator output and the interpolator output.

Abstract: A receiver for a digital communication signal has a first decision gate (DGa), which has a first decision threshold (xd) for outputting a first decision signal, a second decision gate (DGb), which has a second decision threshold (xm) for outputting a second decision signal, a counter (CNT) for counting events where the first and second decision signals of the first and second decision gates (DGa, DGb) differ from each other, and a controller (PROC) capable of controlling the decision thresholds of said first and second decision gates in accordance with count values delivered by said counter. The controller (PROC) determines an initial decision threshold value by performing a statistical analysis of the received signal and setting the decision threshold such that the distribution of logical ‘0’ and logical ‘1’ in the decided signal corresponds to the expected distribution, which is in typically 50%/50%.

Abstract: A timing recovery system and method for accelerated clock synchronization of remotely distributed electronic devices is provided. The system includes a phase locked loop, a linear estimator and control logic. The method includes sampling a clock signal received from an electronic device, applying a linear estimation technique to estimate the frequency and phase of the received signal and providing those estimates to a phase locked loop to accelerate the phase locked loop acquisition rate and secure signal lock quickly.

Abstract: Various apparatus and methods for related to clock recovery are disclosed. For example, in one illustrative embodiment, a clock recovery circuit includes a coding circuit adapted to translate a stream of first digital numbers derived from a source signal into a stream of first binary numbers and a stream of second binary numbers, a digital-to-analog converter (DAC) circuit coupled to the coding circuit and configured to provide an analog output based on the streams of first and second binary numbers and a voltage-controlled oscillator (VCO) controlled by the analog output of the DAC circuit and adapted to produce a base clock having a base clock frequency.

Abstract: A phase measurement circuit is described that receives a signal with irregularly spaced edges and assigns a numerical value to the phase of each edge. An interpolator provides linear interpolation between successive values to provide continuous phase values at smaller, regular intervals. The interpolated values are resampled at a lower, regular rate to simplify subsequent processing by filters or other data-reduction means. The interpolation is performed without dividers or two-variable multipliers.

Abstract: A phase locked loop (PLL) circuit provides ac devices, such as power inverters and power measurement devices, with a reliable means for synchronizing to ac electrical systems. In an exemplary embodiment, the PLL circuit is configured for operation with single-phase electrical systems and offers substantial noise immunity by basing its locking operations on measured fundamental components, i.e., measured x-y phasors, of the electrical system voltage. Further, with its phasor-based locking operations and with its timer/counter-based operation, the PLL circuit can be implemented partly or wholly in digital processing logic.

Abstract: A circuit comprises a first phase detector, a second phase detector, and combinational logic. The first phase detector is for detecting a phase difference between a rising edge of a first clock signal and a rising edge of a second clock signal, and for providing a first difference signal indicating the phase difference. The second phase detector is for detecting a phase difference at a time of a falling edge of the first clock signal and a time of a falling edge of the second clock signal, and for providing a second difference signal indicating the phase difference. The combinational logic is coupled to receive the first difference signal and the second difference signal, and for preventing the second difference signal from being provided when the first difference signal is being provided.

Abstract: A technology capable of avoiding malfunction of a delay locked loop without generating a constant phase error in a delay locked loop circuit is provided. In a delay locked loop circuit, a control circuit is disposed in the outside of a delay locked loop, and in phase comparison of the delay locked loop, the control circuit outputs a control signal to the delay locked loop so that the relation in the phase comparison between a reference signal and an output signal is shifted by a set cycle.

Abstract: A data and clock recovery circuit having a retimer mode and a resync mode. In one embodiment, a receiver circuit includes; a retimer; a clock recovery circuit to provide a clock signal to the retimer; and an adjustable delay to provide a delayed version of an input signal to the retimer. When in a resync mode, the adjustable delay causes a pre-selected delay in the input signal and the clock recovery circuit dynamically selects a clock phase to generate the clock signal. When in a second mode, the adjustable delay dynamically adjusts the delayed version of the input signal and the clock recovery circuit outputs the clock signal having a pre-selected clock phase.

Abstract: An oscillator (30) supplies a high frequency signal (S) to a frequency divider (31). A phase comparator (32) produces a signal measuring phase difference between the divided frequency signal (QA) and a reference signal. A low-pass filter (34) controls the oscillator on the basis of the measurement signal. A measurement window, of duration defined by counting cycles of the high frequency signal, is generated in response to each active edge of the divided frequency signal. The measurement signal is activated during the measurement window so that it comprises, when an active edge of the reference signal falls within the window, a first pulse between the start of the window and this edge and a second pulse, opposite to the first, between this edge and the end of the window.

Abstract: A method and apparatus for clock recovery in synchronous digital systems. The apparatus includes a phase frequency detector, a loop filter, a compressor, and a clock generator. The phase frequency detector generates a phase error signal based on a difference between an input clock signal and an output clock signal. The loop filter multiplies the phase error signal and filters the multiplied phase error signal. The compressor divides the loop filter output. Based on the compressor output, the clock generator generates an output clock signal is provided as a feedback signal to the phase error detector. The apparatus may also include a glitch cleaner for deglitching the input clock signal.

Abstract: A phase locked loop (PLL) architecture provides voltage controlled oscillator (VCO) gain compensation across process and temperature. A simulator may be used to calculate the control voltages for the maximum and minimum output frequency of the VCO for each combination of the process and temperature corners. The maximum and minimum values of control voltage are then selected from these control voltages. Using a counter, the number of cycles of VCO in some cycles of the PLL input clock are counted in binary form and stored in latches for the extreme control voltages. The difference between them and the corresponding difference for typical process and temperature corner is used to modify the charge pump to change the current delivered to the loop filter. After the charge pump bits have been decided, the input control voltage of the VCO connects to the charge pump output to start the normal operation of the PLL.

Abstract: Circuits and methods are provided for adjusting a frequency of a local clock signal in approximating a frequency of a host clock signal. A phase locked loop generates a local clock signal having a first phase and a first frequency. An offset adjustment circuit receives timing information relating the local clock signal to an incoming data signal and calculates a phase offset and a frequency offset indicative of adjustments to be made to the local clock signal. A first phase interpolator generates a receive clock signal from the local clock signal, the receive clock signal having a second phase and a second frequency responsive to the phase and frequency offsets. A second phase interpolator generates a transmit clock signal from the local clock signal having a third frequency responsive to the frequency offset.

Abstract: Alignment of a receiver clock signal with a transmitter clock signal based upon a received data signal is disclosed. Some embodiments generate, based upon of phase bits and valid phase bits, a phase signal having a voltage level selected from at least three voltage levels. One voltage level corresponds to shifting the receiver clock signal in a first direction. Another voltage level corresponds to shifting the receiver clock signal in a second direction. The other voltage level corresponds to repeating a previous shift of the receiver clock signal.

Abstract: Methods and apparatus are provided for improved phase linearity in a multi-phase based clock/timing recovery system. Averaging and interpolation techniques improve phase linearity in a multi-phase clock system. A multi-phase output clock is generated in accordance with one aspect of the invention by generating a plurality of clocks each having a substantially similar frequency and a different phase; applying each of the plurality of clocks to at least one corresponding amplifier such as a differential pair circuit; and summing an output of the corresponding amplifiers to generate the multi-phase output clock. A multiple-stage averaging operation can provide further linearity improvements.

Abstract: A phase-locked loop (PLL) to provide clock generation for high-speed memory interface is presented as the innovate PLL (IPLL). The IPLL architecture is able to tolerate external long loop delay without deteriorating jitter performance. The IPLL comprises in part a common mode feedback circuit with a current mode approach, so as to minimize the effects of mismatch in charge-pump circuit, for instance. The voltage-controlled oscillator (VCO) of the IPLL is designed using a mutually interpolating technique generating a 50% duty clock output, beneficial to high-speed double data rate applications. The IPLL further comprises loop filter voltages that are directly connected to each VCO cell of the IPLL. Conventional voltage-to-current (V-I) converter between loop filter and VCO is hence not required. A tight distribution of VCO gain curves is therefore obtained for the present invention across process corners and varied temperatures.

Abstract: An initialization circuit in a delay locked loop ensures that after power up or other reset clock edges are received by a phase detector in the appropriate order for proper operation. After reset of the delay locked loop, the initialization circuit assures that at least one edge of a reference clock is received prior to enabling the phase detector to increase (or decrease) the delay in a delay line. After at least one edge of a feedback clock is received, the initialization circuit enables the phase detector to decrease (or increase) the delay in a delay line.

Abstract: A phase rotator generates an output signal having plurality of possible output phases with reduced phase jitter. The low jitter phase rotator includes a plurality of differential amplifiers configured to receive a plurality of input differential signals having different phases, and configured to generate a plurality of weighted signals responsive to the plurality of input differential signals. A plurality of digital-to-analog converters (DAC) are arranged into a plurality of groups, each group of DACs configured to provide current for one of the corresponding differential amplifiers. The number of active DACs in each group of DACs determines a relative weighting of the weighted signals, where relative weighting determining an output phase of an output signal of the phase rotator. The DACs are configured to adjust the output phase of the phase rotator. At a kth phase, N/4 adjacent DACs are activated that are indexed as m0, m1, . . . m((N/4)?1), wherein N is the number of said plurality of DACs.

Abstract: A unified, unidirectional serial link is described for providing data across wired media, such as a chip-to chip or a card-to-card interconnect. It consists of a transmit section and a receive section that are operated as pairs to allow the serial data communication. The serial link is implemented as part of a VLSI ASIC module and derives its power, data and clocking requirements from the host modules. The logic transmitter portion contains a phase locked loop (PLL), a dibit data register, a finite impulse response (FIR) filter and a transmit data register. The phase locked loop comprises both a digital coarse loop and an analog fine loop. The digital receiver portion contains a PLL, an FIR phase rotator, a phase rotator control state machine, and a clock buffer. The transmitter and the receiver each preferably utilize a pseudo-random bit stream (PRBS) generator and checker.

Abstract: Techniques are provided for calculating a clock rate for a serial clock of a transmitter where information sent by the transmitter is sent in packets from the transmitter over an asynchronous network. The techniques involve minimizing the number of adjustments to the clock rate that are needed to fine tune the clock rate to match the serial clock of the transmitter.

Abstract: A method for automatically calibrating intra-cycle timing relationships between command signals, data signals, and sampling signals for an integrated circuit device. The method includes generating command signals for accessing an integrated circuit component, accessing data signals for conveying data for the integrated circuit component, and accessing sampling signals for controlling the sampling of the data signals. A phase relationship between the command signals, the data signals, and the sampling signals is automatically adjusted to calibrate operation of the integrated circuit device.

Abstract: A display apparatus including an analog-to-digital converter (ADC) module, a phase detecting module, and a clock generator is provided. The ADC module is used to receive a first analog video signal, and convert the first analog video signal into a digital signal according to a clock signal. The first analog video signal includes a first synchronous information and a first video information. The phase detecting module is used to receive the digital signal, and output a phase adjustment signal according to a part of the digital signal corresponding to the first synchronous information. The clock generator is used to output the clock signal according to the phase adjustment signal.

Abstract: A dual loop, clock synchronization circuit for a receiver in a communication system. The circuitry uses a first loop of a digital phase lock loop for coarse synchronization to time stamps within the received data and uses a second loop for fine synchronization of a second numerically controlled oscillator.

Abstract: A self-tuning 3rd order type III phase-locked loop (PLL) is disclosed. In one aspect, the PLL provides frequency control that is implemented in three (3) parallel paths. The PLL provides frequency response tracking using a number of elements including a triple control voltage-controlled oscillator (VCO), a frequency-to-current (F2I) converter, and a switched capacitor loop filter. In addition to compensation for feedback ratio variation, near constant F2I gain over process variations and switched capacitor filters synchronized to a reference signal, near constant VCO gain over process variations allows the open loop frequency response to be tailored to track the reference signal. A high-speed locking technique is employed which significantly reduces acquisition time in low bandwidth cases. This PLL may be fabricated in a 0.18 ?m CMOS logic process.

Abstract: A device is for detecting a relative positioning of two clock signals including a fast clock signal and a slow clock signal. The fast clock frequency may be n times greater than a slow clock frequency, and n includes an integer greater than 1. The device includes a phase logic signal generator for generating a phase logic signal from the two clock signals by assigning a predetermined logic value to the phase logic signal when a rising edge of the fast clock signal matches a predetermined location of the slow clock signal.

Abstract: The timing synchronization module includes a phase locked loop (PLL) and a synchronization processing unit. The PLL receives an output-end clock signal. When the PLL receives the output-end clock signal for the first time, the PLL generates a reception-end clock signal according to the output-end clock signal. The synchronization processing unit receives a procedure clock signal and the reception-end clock signal. The output-end clock signal has M clocks after the reception-end clock signal is generated, while the reception-end clock signal has N clocks as generated. When the difference value of M and N is larger than a preset value, the synchronization processing unit removes the media signal corresponding to the procedure clock signal and generates the reception-end clock signal again. When the difference value is smaller than the preset value, the synchronization processing unit controls media signal playing according to the reception-end clock signal and the procedure clock signal.

Abstract: A clock synchronization buffer for a counter clock flow pipelined circuit including a cascade of processing modules that receive data from a previous module and provide output results to a following module. The clock synchronization buffer receives a clock input signal and provides clock signals to a local processing module and to the next pipeline stage. The clock synchronization buffer includes a selectable delay stage that receives a clock input signal and a delay select signal and outputs a clock signal having a selected delay. An amplifier connected to the selectable delay stage provides the delayed clock signal to a local processing module that corresponds to the clock synchronization buffer circuit. An inverting amplifier connected to the selectable delay stage provides the delayed clock signal to the next pipeline stage. A clock synchronization controller synchronizes the phases of reference clock input and synchronized clock input signals.

Abstract: An apparatus that reduces sampling errors for data communicated between devices uses phase information acquired from a timing reference signal such as a strobe signal to align a data-sampling signal for sampling a data signal that was sent along with the timing reference signal. The data-sampling signal may be provided by adjustably delaying a clock signal according to the phase information acquired from the strobe signal. The data-sampling signal may also have an improved waveform compared to the timing reference signal, including a fifty percent duty cycle and sharp transitions. The phase information acquired from the timing reference signal may also be used for other purposes, such as aligning received data with a local clock domain, or transmitting data so that it arrives at a remote device in synchronism with a reference clock signal at the remote device.

Abstract: A frequency-to-current converter includes a digitally selectable capacitor, a sampling capacitor, an integrator circuit and an output transconductor. The sampling capacitor is operatively coupled via a first switch to the digitally selectable capacitor. The first switch is operated by a first clock pulse from a clock generator responsive to a reference clock. The integrator circuit has an output operatively coupled via a second switch to the sampling capacitor. The integrator circuit has an output operatively coupled to a control terminal of the transistor. The second switch is operated by a second, non-overlapping clock pulse from the clock generator. A current output by the frequency-to-current converter in response to the continuous question of first and second switches is linearly proportional to the frequency of the reference clock and the capacitance of the digitally selectable capacitor.

Abstract: An apparatus and a method for tracking a sampling clock of a multi-carrier communication system are disclosed, the apparatus including a data removal module, a phase estimation module, and a sampling clock offset computation module. The data removal module is for generating a plurality of first and second data removal symbols by removing predetermined transmitted data from a plurality of first and second received symbols, respectively. The phase estimation module for generating a first and a second phase shifts according to correlations of the plurality of first and second data removal symbols. The sampling clock offset computation module for generating a control signal utilized to compensate the sampling clock of a plurality of received symbols according to the first and a second phase shifts.

Abstract: A clock and data recovery circuit includes a phase detector configured to compare a phase of a data signal to a phase of a sampling clock to provide a phase error signal, a gain stage configured to apply a gain to the phase error signal to provide an amplified phase error signal, and a filter configured to filter the amplified phase error signal to provide a phase correction signal. The circuit includes a gain controller configured to adjust the gain of the gain stage in response to the phase correction signal, and a clock generator configured to provide the sampling clock based on the phase correction signal.

Abstract: In an apparatus and method for checking a network synchronization clock signal in a communication system, the apparatus generates a divided clock signal which is the same as an externally inputted network synchronization clock signal, compares the value of one period of the network synchronization clock signal to the value of one period of the divided clock signal, and determines whether the network synchronization clock signal is normal or not. Thus, the reliability of an operation of checking the network synchronization clock signal is enhanced.

Abstract: A carrier recovery method and apparatus using multiple stages of carrier frequency recovery are disclosed. A receiver uses multiple frequency generation sources to generate carrier signals used to downconvert a received signal. An analog frequency reference having a wide frequency range and coarse frequency resolution is used in conjunction with a digital frequency reference having a narrow frequency range and fine frequency resolution. The multiple carrier signals are multiplied by a received signal to effect a multi-stage downconversion, resulting in a baseband signal. A frequency tracking module measures the residual frequency error present in the baseband signal. The measured residual frequency error is then used to adjust the frequencies of the carrier signals generated by the multiple frequency generation sources.

Abstract: The present invention includes apparatus and methods to calibrate a phase detector and an analog-to-digital converter (ADC) offset and gain. In one such embodiment, an apparatus includes a phase detector to generate an error pulse and a reference pulse, a combiner to combine the pulses, and an ADC to receive the combined pulses, where the ADC has a full scale set by an average of the reference pulse. Still further, a calibration loop may be coupled between the output of the ADC and the phase detector to generate and provide a phase adjust signal to reduce or eliminate phase offsets. Other embodiments are described and claimed.

Abstract: A phase detector apparatus and method used for clock recovery from a data signal is provided. The phase detector provides phase correction signals to a clock signal generator, where the phase correction signals are only generated if a predetermined data sample pattern is observed. In particular, the predetermined data sample pattern is preferably a transition from one to zero. Thus, transitions from zero to one will not provide a valid phase update output signal, even though a transition has occurred. In other embodiments the predetermined data sample pattern is preferably a one to zero transition preceded by an additional logic one sample.

Abstract: A clock recovery circuit for digital data transmission includes a delay lock loop having a first loop which generates a phase difference signal which is indicative of a quantized phase difference between a data signal and a clock signal; and a second loop which generates a phase difference signal which is a smooth, continuous function of the phase difference between the data signal and the clock signal, such as a phase difference signal which is proportional to the phase difference. The delay lock loop may include two phase shifters in series, and one or both of these may include a phase interpolator.

Abstract: A transceiver providing Fiber Channel data transfer speeds may be implemented in a lower performance process technology as a single unit, thereby reducing cost. A serializer and deserializer each having multiple lower frequency clocks are provided to obtain the equivalent of a high speed clock capable of use in Fiber Channel systems. Lower speed parallel data is converted to higher speed serial data, and vice versa. A digital frequency counter along with a phase detection circuit provides synchronization. Comma detection is provided for data word alignment.