Phaselock techniques are often used to establish coherence. 2. A phaselocked loop can be used as a frequency demodulator, in which service it has superior. Phaselock Techniques, Third Edition is intended for practicingengineers, researchers, and graduate students. This criticallyacclaimed book has. Loading The author, Floyd M. Gardner an influential expert in the area of PLLs, has presented a good reference book that encompasses all.
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Search the history of over billion web pages on the Internet. Full text of ” Electronics: Now greatly expanded and largely rewritten to reflect a better understanding of the subject, the book presents much recent material, some published here for the first time.
Ex- planation of fundamentals is improved and expanded, and description of appli- cations is greatly increased. Most of this material has been rewritten from the first edition. The ma- terial that follows deals with practical as- pects of component circuits and with ra- tional procedures for deciding upon phaselocic loop parameters.
This ail- new examination of loop components Is found nowhere else In today’s literature. Included are discus- sions of phaselocked modulators and demodulators, synthesizers, receivers, transponders, oscillator stabilizers, and data synchronizers.
He engaged In basic phaselock reseai in circuit design, in debugging of phs lock hardware, and in the teaching phaselock courses. Phaselkck has been an indepenc consulting engineer since Besli phaselock, he has been involvec such diverse topics as digital commi cations especially synchronizationlemetry, electronic tracking and nav tion systems, and design of radio ceivers.
For these readers the book discusses basic principles of phaselock operation, typical prac- tices of phaselock engineering, and selected applications of phaselock to various problems. Long mathematical derivations have been avoided on the premise that they are of little interest to the practicing engineer. Instead, I have tried to outline the underlying assumptions and methods employed in derivations and have garnder practical results. For those readers who may be inter- ested in further details, I have listed nimierous references.
On the other hand, I have avoided producing a circuits cookbook. Specific circuits quickly become obsolete; furthermore, very little funda- mental understanding can be gained from a collection of circuit recipes.
I have tried to stress physical imderstanding of basic phenomena as much techniuqes possible. Nonetheless, because many aspects of phaselock can be expressed only in mathematical terms, the largest part of the material tecgniques presented here in that form. As a consequence, the reader must have some mathematical background. For fullest understanding of the subject trchniques familiarity with transfer functions in the Laplace transform notation, a background in feedback or servo theory, and a nodding acquaintance with noise and spectral analysis of stochastic processes are needed.
The results and applications are presented so that a less well-prepared reader can under- stand them, but the minimum phasepock are necessary for a full under- standing of the detailed basic principles.
This philosophy underlay the first edition of this book, which was well received by its intended audience. In the years since its pubUcation much has happened in the phaselock world. Better analyses have been per- formed, new circuits have arisen and old ones have faded awaymore vii viii Preface applications have appeared, and my own understanding of phaselock has improved substantially.
Thxis the time seems ripe for a new edition. The reader will find additional analytical tools and improved explana- tions of the fundamentals of the subject. Moreover, the material on applications has been expanded greatly. I hope the profession finds this book to be as useful as its predecessor.
I have benefited from the wise counsel of J. Caicthik, each of whom reviewed one or more chapters. Their expert critiques have made this book better than it would have been through my unaided efforts. Lock Limits, 53 References, 63 5 Acquisitioii 5. A phase detector PD. A voltage-controlled oscillator VCOwhose frequency is controlled by an external voltage. The phase detector compares the phase of a periodic input signal against the phase of the VCO; output of the PD is a measure of the phase difference between its two inputs.
The difference voltage is then filtered by the loop filter and applied to the VCO. Control voltage on the VCO changes the frequency in a direction that reduces the phase difference between the input signal and the local oscillator. When the loop is locked, the control voltage is such that the frequency of the VCO is exactly equal to the average frequency of the input signal.
For each cycle of input there is one, and only one, cycle of oscillator output. One obvious application of phaselock is in automatic frequency control AFC. Perfect frequency control can be achieved by this method, whereas conventional AFC techniques necessarily entail some frequency error. To maintain the control voltage needed for lock it is generally necessary to have a nonzero output from the phase detector.
Consequently, the loop operates with some phase error present; as a practical matter, however, this error tends to be small in a weU-designed loop. A slightly different explanation may provide a better understanding of loop operation. Let us suppose that the incoming signal carries information in its phase or frequency; this signal is inevitably corrupted by additive noise. Technkques task of a phaselock receiver is to reproduce the original signal while removing as much of the noise as possible.
Phaselock Techniques – Floyd M. Gardner [Book review] | GaussianWaves
To reproduce the signal phaseloock receiver makes use of a local oscillator whose frequency is very close to that expected in the signal. Local oscillator and incoming signal waveforms are techmiques with one another by a phase detector whose error output indicates instantaneous phase difference. To suppress noise the error is averaged over some length of time, and the average is used to establish frequency of the oscillator. If the original signal is well behaved stable in frequencythe local oscillator will need very phaselocl information to be able to track, and that information can be obtained by averaging for a long period of time, thereby eliminating noise that could be very large.
The input to the loop is a noisy signal, whereas the output of the VCO is a cleaned-up version of the input. It is reasonable, therefore, to consider the loop as a kind of filter that passes signals and rejects noise.
Two important characteristics of the filter are that the bandwidth can be very small and that the filter automatically tracks the signal frequency. These features, automatic tracking and narrow pgaselock, account for the major uses of phaselock receivers. Narrow bandwidth is capable of reject- ing large amounts of noise; it is not at all unusual for a PLL to recover a signal deeply embedded in noise.
Superheterodyne receivers had come into use during the s, but there was phaseloxk continual search for a simpler technique; one approach investigated was the synchro- nous, or homodyne, receiver.
History and Application 3 In essence, this receiver consists of nothing but a local oscillator, a mixer, and an audio amplifier.
To operate, the oscillator must be adjusted to exactly the same frequency as the carrier of the incoming signal, which is then converted to an intermediate frequency of exactly 0 Hz. Output of the mixer contains demodulated information that is carried as sidebands by the signal.
Interference will not be synchronous with the local oscillator, and therefore mixer output caused by an interfering signal is a beat-note that can be suppressed by audio filtering.
Correct tuning of the local oscillator is essential to synchronous recep- tion; any frequency error whatsoever will hopelessly garble the informa- tion. Furthermore, phase of the local oscillator must agree, within a fairly small fraction of a cycle, with the received carrier phase. In other words, the local oscillator must be phaselocked to the incoming signal. For various reasons the simple texhniques receiver has never been used extensively.
Present-day phaselock receivers almost invariably use the superheterodyne principle and tend to be highly complex. One of their most important applications is in the reception of the very weak signals from distant spacecraft. The start of each line and the start of each interlaced half-frame of a television picture are signaled by a pulse transmitted with the video information. As a very crude approach to reconstructing a scan raster on the TV tube, these pulses can be stripped off and individually utilized to trigger a pair of single- sweep generators.
A slightly more sophisticated approach uses a pair of free-running relaxation oscillators to drive the sweep generators. In this way sweep is present even if synchronization is absent. Free-running frequencies of the oscillators are set slightly below the horizontal and vertical pulse rates, and the stripped tecgniques are used to trigger the oscillators prematurely and thus to synchronize them to the line and half-frame rates half-frame because United States television interlaces the lines on alternate vertical scans.
In the absence of noise this scheme can provide good synchronization and is entirely adequate. Unfortimately, noise is rarely absent, and any triggering circuit is particularly susceptible to it. As an extreme, triggered scan will completely fail at a signal-to-noise ratio that still provides a recognizable, though inferior, picture. Under less extreme conditions noise causes starting-time jitter and occasional misfiring far out of phase.
Horizontal jitter reduces horizontal resolution and causes vertical lines to techniquss a ragged appearance. Severe horizontal misfiring usually causes a narrow horizontal black streak to appear. Also, the interlaced lines of successive half-frames would so move with tehcniques to one another that further picture degradation would result.
Full text of “Electronics: Phaselock Techniques (F Gardner )”
Noise fluctuation can be vastly reduced by phaselocking the two oscilla- tors to the stripped sync pulses. Instead of triggering on each pulse, a phaselock technique examines the relative phase between each oscillator and many of its sync pulses and adjusts oscillator frequency so that the average phase discrepancy is small.
Because it looks at many pulses, a phaselock synchronizer is not confused by occasional large noise pulses that disrupt a triggered synchronizer. The flywheel synchronizers in pres- ent-day TV receivers are really phaselocked loops. The name “flywheel” is used because the circuit is able to coast through periods of increased noise or weak signal. Substantial improvement in synchronizing performance is obtained by phaselock.
In a color television receiver, the color burst is synchronized by a phaselock loop. Space use of phaselock began with the launching of the first American artificial satellites.
These vehicles carried low-power 10 mW CW transmitters; received signals were correspondingly weak. Because of Doppler shift and drift of the transmitting oscillator, there was consider- able uncertainty about the exact frequency of the received signal.
However, the signal itself occupies a very narrow spectrum and can be contained in something like a 6-Hz band- width. Noise power in the receiver is directly proportional to bandwidth. Therefore, if conventional techniques were used, a noise penalty of times 30 dB would have to be accepted.
The penalty for conventional techniques would thus be about 47 dB. Such penalties are intolerable and that is why narrowband, phaselocked, track- ing receivers are used. Noise can be rejected by a narrowband filter, but if the filter is fixed the signal almost never will be within the passband. For a narrow filter to be usable it must be capable of tracking the signal.
A phaselocked loop is capable of providing both the narrow bandwidth and the tracking that are needed. Moreover, extremely narrow bandwidths can be conveniently PhaselocK Literature 5 obtained 3 to Hz are typical for space applications ; if necessary, bandwidth is easily changed.
For a Doppler signal the information needed techniwues determine vehicle velocity is the Doppler frequency techniquws.