Hewlett-Packard Company

Leland Stanford Junior University

David C Chu

Jeremy S Sommer

Alistair D Black

David W Clark

Thomas Allen Knotts

Keith M Ferguson

Michael J Ward

Lee D Cosart, Iii

John H Gliever

Atul Tambe

Alan Davis

James R Fienup

Robert W Offermann

A feed forward apparatus and method discipline a clock signal by a reference signal in digital telecommunication networks. A synthesizer correction term within the feed forward apparatus and method includes a frequency correction term so that when one frequency correction term is selected in place of another frequency correction term the phase of the clock signal remains free from extraneous frequency or phase variations during the transition between frequency correction terms. Alternatively, the synthesizer correction term includes a phase correction term so that phase coherence between the reference signal and the clock signal results.

Feed forward method and apparatus for generating a clock signal

In the present embodiment, digital phase detection of digital telecommunications signals is based on heterodyning. The frequency of two signals are scaled to different nominal values that are separated by a typically small but finite difference. The two frequencies are then mixed to generate a finite beat frequency. In mixing, phase is preserved and the finite beat frequency phase is in one-to-one correspondence with the signal phase. Phase detection is performed indirectly at the lower finite beat frequency with high resolution and greater ease than direct phase detection.

Digital phase detector

A master and a slave digital frequency synthesizer are phase-locked such that the master synthesizer is always selected to minimize the phase hits which occur when switching the master to be a slave and vice versa. The switching rearrangement is done automatically and rapidly in the event of failure of the master frequency synthesizer.

Phase-locked digital synthesizers

A system for characterizing phase modulated signals, e.g., .pi./4 DQPSK signals, includes a time interval analyzer coupled to a system processor for determining a variety of signal characterizing parameters as a function of readings made on a phase modulated signal by the analyzer. The system processor includes a phase/frequency determining section for generating a phase deviation curve and decoding the modulated signal. The system processor further includes a processing section for determining various signal defining parameters including origin offset and I/Q mismatch as a function of the phase deviation.

System for characterizing phase-modulated signals using a time interval

A system for recovering parameters of an underlying clock signal from data modulated signals includes a time digitizer, or time stamping device, for sampling and locating edges of the data modulated signals, thereby selectively providing time stamp readings identifying incoming edges of the data signals. The time stamp readings are used, along with a user-input nominal clock frequency, to determine an array of actual clock cycle stamps, each representing an integral number of actual clock cycles occurring between adjacent time stamps. The array is then used in conjunction with the time stamps to characterize parameters of the underlying clock data. Once the clock parameters are recovered, a wide variety of information, for example, frequency and phase information, including jitter, can be determined with a very modest rate of sampling compared to the high data bandwidth. No phase locked loops are used and no physical clock is recovered. The system is operable over a well-defined range and is highly repeatable, independent of particular circuit design detail or parametric performance of circuit components.

System for highly repeatable clock parameter recovery from data

A method and apparatus for the measuring of a delay in a delay circuit by making a continuous frequency measurement is proposed. The phase-locking of a variable frequency signal applied to the delay circuit allows the user to significantly improve the precision and accuracy of the time delay measurement. A scheme to extract the number of cycles stored in the delay circuit is also disclosed.

Precision timed delay measurement using phaselocked CW technique

A circuit for time stamping event signals, e.g. zero-crossings, using coarse and fine timers. The fine timer is a circuit section which subdivides a period from a phase-locked ring-oscillator into 2N subparts. An event signal is timed by latching a digital representation of a particular subpart. The digital representation of the subpart is an N-bit dual thermometer code which uniquely identifies each subpart with each adjacent subpart differing by only one bit. The subparts are made finer in time quantization than the propagation delay of one active element in the ring oscillator by the use of linear combiner elements. The dual thermometer code, encoded post-latching into a binary code, forms the 'fine' timing part of a binary word representation of the event time. The event also latches the count states of a pair of lead-lag counters in a master-slave configuration counting ring oscillator periods. These counters change states respectively before and after the dual thermometer code turn-overs. Only one reading is chosen for recording as determined by the most significant bit of the fine code. The choice will always find an accurate and stable reading, and reject erroneous readings resulting from reading a counter in transition. The chosen counter reading, encoded to binary, forms the coarse timer for the binary word representation of the event time. The coarse and fine binary words are butt-joinable to form the complete binary timing representation without further arithmetic processing.

Picosecond event timer

A method and apparatus makes rapid frequency measurements by measuring time intervals for a series of blocks of event counts with the number of events in each block held constant. This makes the numerator of the events/time relationship constant so it does not have to be measured, processed or stored. The frequency of the signal is determined by measuring the time interval, then taking the inverse of the measured value and multiplying by the appropriate constant. A fast inverse circuit uses a Taylor series expansion technique implemented in digital circuit, with the slope resolution adjusted for regions of small slope to improve accuracy.

Constant events frequency measurement and fast inverse circuit

A method of digitally controlling the gate for a timing counter, to open and close the gate based on the occurrence of signal events, rather than on the envelope of the pulse. In a particular embodiment, a digital divider controls the gate, so that, when a pulse burst of RF is encountered, the gate opens on the second signal event. The divider can be programmed to close the gate any number of signal events later. Measurements are taken for an integral number of signal events, while counting time events from a precision clock. A series of measurements can be taken with various integral numbers of signal events for frequency profiling. By incrementing the digital divider from n to n+1 signal events for successive measurements, and subtracting the results, very narrow gates are effectively generated which move through the pulse cycle by cycle for frequency profiling. Because the opening of the gate is triggered by the IF events themselves, the gate is reliably and accurately positioned with respect to the pulse, and is unaffected by jitter in the pulse repetition interval.

Digital gate generation for a signal measurement instrument

A method and apparatus is presented for calibrating instruments for time interval measurements, pulse width measurements, and rise and fall time measurements. The preferred method comprises generating two coherent pulses using a linear passive device. The coherent pulses are simultaneously a.c. coupled to two channels of, for example, a time-interval measuring instrument. The time interval between the coherent pulses passing through the instrument is measured at identical voltages on each signal. Then the coherent pulses are exchanged between the channels and a further interval measurement is made. The results of each of the measurements are compared and used to calculate calibration constants to correct systematic errors present in the instrument.

Method for calibrating instruments for time interval measurements

A time interval measuring apparatus is provided for measuring the time interval between two signals. The two signals are successively brought to synchronization by delaying one of the two signals as they pass through a series of time shift cells connected in tandem. These delays are accumulated in a register, and the total net delay which is required to bring the two signals into synchronization is indicative of the time interval between the two signals. This indication of the time interval between the two signals thus forms the time interval measurement thereof. It can be refined by increasing the number of time shift cells in tandem and using progressively finer delays.

Time interval measuring apparatus and method

A method of sampling accurately the instantaneous content of a high speed counter without interrupting the counting process is provided. The method is applicable even when the higher order digits of the counter are constructed by slower switching circuits configured in either a synchronous or ripple-through arrangement. The switching and carry propagation times of these higher order counters need not be shorter than the time between successive events being counted. Sampling of the contents may be made repeatedly in the interim without affecting the totality of the final count.

Data capture in an uninterrupted counter

A method is provided for measuring a single-shot time interval using startable oscillators to replicate indefinitely the time interval for averaging. Also provided is a circuit for automatically selecting a proper ratio of division to ensure that the interval being measured is less than the period of replication.

Automatic echo-chamber for measuring single time intervals by

Measurement of a time interval between a start and a stop event is made by activating a start oscillator in response to the start event and activating a stop oscillator in response to the stop event. The number of cycles of each respective oscillator signal which occur between the activation of each oscillator and the coincidence of the respective oscillator signal with that of an independent time base is determined. The number of cycles of the time base signal between the coincident points of it and the start and stop oscillator signal is also determined. These numbers, which are always integers, are used along with the values for the time base period and the difference in frequency between the time base oscillator and the start and stop oscillators to calculate the time interval. Resolution of the measurement is dependent on the frequency difference between the time base signal and the start and stop oscillator signals. Two triggered-phase oscillators, which are phase-locked to the reference oscillator, are used to supply the start and stop frequencies. The start trigger and stop signals are used for phase shifting, i.e., restarting of the oscillators rather than starting the oscillators. This allows for pre-trigger frequency control, and essentially eliminates post trigger frequency drift which usually occurs when an oscillator is first started. The coincidence signals are provided by the phase cross-over between the phase locked oscillator and the reference by a digital mixer.

Double vernier time interval measurement using triggered phase-locked

An automatic transfer oscillator system for frequency measurement using a single sampler is described. Two signals, of frequencies f.sub.1 and f.sub.2, are alternately used to drive the sampler. The two frequencies are sufficiently close by design so that the intermediate frequency signals generated arise from the same harmonic number when sampling a signal of unknown frequency f.sub.x. The resulting average IF output is accurately measured and used to compute the unknown frequency f.sub.x. Accurate measurement of the average IF output is made possible because the transition between f.sub.1 driving the sampler and f.sub.2 driving the sampler only occurs when the two signals are in phase. As a result, the IF signal transitions are also in phase and spurious signals are not produced. This technique is referred to as phase continuous switching.

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Woodside, CA, United States of America

David C Chu