Crystal Oscillator Design And Temperature Compensation Pdf
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- Crystal Oscillator Design and Temperature Compensation
- Design Technique for Analog Temperature Compensation of Crystal Oscillators
- crystal oscillator pdf
Crystal Oscillator Design and Temperature Compensation
It shows how to design and optimize nearly any crystal oscillator used in commercial or military electronics, including logic gate and integrated circuit oscillators, and covers fully the latest technology in the field. A selection guide is included which allows the designer to choose the best circuit for his specific application.
Each oscillator circuit is analyzed, with its design equations and optimization procedures. Schematic diagrams for more than 20 circuits are included, with equations covering the entire frequency spectrum from several kHz to MHz. The author provides a brief but comprehensive survey of basic oscillator theory, quartz crystal technology, and active circuits prior to discussing actual oscillator design.
Also presented are tests which can be conducted on the engineering models to determine with reasonable assurance whether the circuit will perform properly when produced in quantity. A thorough treatment of temperature compensation is presented that enables the design engineer to improve the stability of the oscillator by as much as two orders of magnitude. A unique method using a microprocessor is compared w i t h three other methods of temperature compensation currently in use or under development-analog, digital, and hybrid.
Please note that this is not an exclusive license but that I will retain all other rights to the book, e. ForewordCrystal oscillators have been in use now for well over 50 years-one of the first was built by W. Cady in Today, millions of them are made every year, covering a range of frequencies from a few Kilohertz to several hundred Megahertz and a range of stabilities from a fraction of one percent to a few parts in ten to the thirteenth, with most of them, by far, still in the range of several tens of parts per million.
Their major application has long been the stabilization of frequencies in transmitters and receivers, and indeed, the utilization of the frequency spectrum would be in utter chaos, and the communication systems as we know them today unthinkable,'without crystal oscillators.
With the need to accommodate ever increasing numbers of users in a limited spectrum space, this traditional application will continue to grow for the foreseeable future, and ever tighter tolerances will have to be met by an ever larger percentage of these devices.
Narrowing the channel spacing-with its concomitant requirements for increasingly more stable carrier frequencies-is but one of the alternatives to increase the number of potential users of the frequency spectrum. Subdividing the time during which a group of users has access to a given channel is another; and many modern radio transmission systems make use of this principle.
Here again, the crystal oscillator plays a dominant role; not to control the carrier frequency, but to keep the time slots for the various users coordinated, that is, to serve as the clock rate generator of the systems clocks in transmitters and receivers. The demands on oscillator performance are often even more stringent in this application than for carrier stabilization alone. The use of crystal oscillators as clock rate generators has seen a rate of growth in the recent past that is nothing short of explosive, with no end in sight yet, in applications that are quite unrelated to the communications field, such as in the quartz wrist watch and in the microprocessor.
Other uses include reference standards in frequency counters and time interval meters, gauges for temperature and pressure, and instruments for the measurement of mass changes for scientific and environmental sensing purposes, to name just a few. In short, the crystal oscillator is now more in demand than ever, and the need for improved performance in mass producible devices becomes more urgent with V vi Foreword nearly every new application. An increasing number of engineers, therefore, find themselves confronted with the challenge of designing crystal oscillators with near optimum performance, as tailored to a specific application.
Those new in the field are bound to discover very soon that there is no substitute for a considerable amount of hands-on experience. Rarely can a circuit reported on in the literature be used without modifications, and details, not discussed fully in the descriptions provided, are often found to be significant. The possible combinations of circuit elements that make a viable oscillator are nearly limitless, and while most experienced designers have gravitated toward a few basic configurations, no one circuit, or even small group of circuits, has as yet evolved that is, in all details, universally suitable.
Nor does it appear likely that this will happen in the foreseeable future, if for no other reason than because new active devices are continually being brought to market, with often significant advantages for use in oscillator circuits, but requiring different conditions for proper operation.
The general principles of crystal oscillator design, however, remain. The basic building blocks of a crystal oscillator are the feedback circuit containing the crystal unit; the amplifier containing one or more active devices; and circuitry or devices such as needed for modulation, temperature compensation or control, etc.
What is needcd most by the circuit dcsigncr is a clear approach to undcrstanding the interrelationship'of the various circuit elements within each of these building blocks and of the blocks with one another. And this holds true whether the goal is an oscillator, hand-tailored in small quantities to achieve the highest performance possible, or mass produced and capable of meeting the specified requirements under worst case conditions.
While such approaches do exist, their exposition in the literature is scarce. It is to fill this void that Mr.
Frerking has written this book. Frerking is surely one of the most accomplished and innovative practitioners of the art of crystal oscillator design, with extensive experience in the development of high performance oscillators for high volume use. In his book he shares with the reader the design techniques that he has found most useful and conveys a wealth of practical information that will be of immediate use to engineers who are faced with the challenge of designing a crystal oscillator for todafs more demanding applications.
AcknowledgmentsThe author wishes t o express his sincere appreciation to the Collins Telecommunications Products Division of Rockwell International whose support and facilities made this work possible, and to those engineers working in the field of frequency control whose contributions have resulted in many of the techniques described in this book. The author would also like to acknowledge the assistance rendered by Dr 20 output impedance 2 , reverse transfer impedance I n troduct ionThe increasing demand in radio communications for channel space as well as the use of sophisticated navigation systems and data transmission has resulted in increased frequency stability requirements in many items of equipment.
As a result, the demands on crystal oscillators have become more stringent. In many cases, it is no longer sufficient merely to use a crystal oscillator; now it is necessary to take measures to ensure that the crystal oscillator will possess a high degree of frequency stability. Designs of this type are often quite difficult for the engineer who has had little or no prior experience with crystal oscillators; consequently, much of the material in this book is directed to the individual who has a good background in circuit theory but who is not necessarily experienced with crystal oscillator design.
The book deals primarily with transistor oscillators, since nearly all precision oscillators at the present time use discrete transistors. The use of gate oscillators and clock oscillator integrated circuits is widespread in lower stability applications, and these are discussed in Chapter 7. A practical treatment of quartz crystal resonators is presented in Chapter 5 which gives the designer a good working knowledge of the devices.
In Chapter 6 , the nonlinear properties of transistors are explored to enable prediction of the amplitude of oscillation and the harmonic content for various oscillators. Chapter 7 then brings together all the information already presented and presents the actual design equations for oscillators covering the entire frequency spectrum from several kHz to MHz. It also includes over 20 tested circuits with component values. Crystal oscillators, in general, are more critical than most electronic circuits.
As such, it behooves the design engineer to take special precautions to ensure that his oscillator circuit will perform Basic Oscillator TheoryIn undertaking the design of a crystal oscillator, an understanding of basic oscillator principles is not only desirable but essential.
Therefore, a brief explanation of the operation of a crystal oscillator is given here. Basically, a crystal oscillator can be thought of as a closed loop system composed of an amplifier and a feedback network containing the crystal. Amplitude of oscillation builds up to the point where nonlinearities decrease the loop gain to unity. The frequency adjusts itself so that the total phase shift around the loop is 0 or degrees. The crystal, which has a large reactance-frequency slope, is located in the feedback network at a point where it has the maximum influence on the frequency of oscillation.
A crystal oscillator is unique in that the impedance of the crystal changes so rapidly with frequency that all other circuit components can be considered to be of constant reactance, this reactance being calculated at the nominal frequency of the crystal. The frequency of oscillation will adjust itself so that the crystal presents a reactance t o the circuit which will satisfy the phase requirement.
If the circuit is such that a loop gain greater than unity does not exist at a frequency where the phase requirement can be met, oscillation will not occur. The application of these principles to oscillator design usually is difficult because many factors play an important part in the operation. As a result, the design of transistorized crystal oscillators is often a "cut and try" procedure. Methods have been developed for predicting the amplitude of oscillation based on the small-signal loop gain.
The reduction in gain for a transistor operating at large signal values is predictable and has been plotted as a function of the ac base-to-emitter voltage. Since it is known that the loop gain after equilibrium has been reached will be unity, the reduction factor is numerically equal to the small-signal loop gain.
Using this value, the amplitude of oscillation can be predicted from the graphs. The first, which is highly experimental, consists of giving a qualitative explanation of how the circuit works and presenting a number of typical schematic diagrams for that oscillator configuration.
The second method consists of deriving the equations for oscillation in terms of the Y-parameters of the transistor. The third method consists of measuring the gain and input impedance of the transistor as a function of its load impedance. This information is used to calculate component values for the circuit with relatively simple equations.
The amplitude of oscillation can then be predicted using the methods of paragraph 3. To assist in this design approach, Chapter 7 contains a number of laboratory tested oscillator circuits and a qualitative explanation of their operation. The appropriate circuit type most suited for a particular application can be selected with the aid of Table The individual circuits have not been designed or optimized with respect to any particular performance characteristic, but sufficient reserve gain has been provided to allow some modification.
The following precautionary items must be presented in regard to the use or modification of any of these circuits: a. Since the mechanical arrangement of a circuit usually affects its performance, complete testing of the circuit in accordance with Chapter 8 should be accomplished even though the circuit values presented are used.
The equations and the assumptions made are presented for the various oscillators in Chapter 7. Since the equations in general do not give highly accurate results, it is well to use them in connection with the experimental approach see section 3. However, the equations do give an indication of how changing a given component will affect the overall performance and thus are often quite useful.
The equations are generally of the form takes place as a result of the base-to-emitter junction being cut off during part of the cycle, the amplitude of oscillation can be predicted using Figure Limiting of this type generally results in good frequency stability.
The oscillator may be biased to produce collector limiting. If this is the case, the output voltage can be determined by constructing a load line as shown in Figure The peak output voltage will be approximately VI or V,, whichever is smaller.
This is a rule of thumb only and not highly accurate. The oscillator should be designed to require the same crystal reactance X , as that called out by the crystal specification for onfrequency operation. Phase shift considerations are taken care of experimentally by getting the crystal to operate on frequency. The usefulness of this design approach generally is limited to series mode oscillators which can be represented by the block diagram of Figure The power gain required from the transistor must be sufficient to supply the output power, power losses, and the input power requiredStep 1.
Connect the transistor as a single-tuned amplifier in the grounded-base or grounded-emitter configuration, whichever is to be used in the type of oscillator being designed. A circuit similar to that of Figure 3 -4 may be used. The circuit should be arranged so that it can be mounted on the impedance measuring device such as a network analyzer or RX meter with the input near the ungrounded terminal. Provisions should be made for connecting RF voltmeters to the input and output of the transistor.
Design Technique for Analog Temperature Compensation of Crystal Oscillators
Product status. Product height is maximum value. PDF flyers for product lineup and new product information are available. Product list that have been discontinued, are planning to discontinue, or are NRND. TCXO Temperature compensated crystal oscillator is a type of crystal oscillator. TCXOs provide a stable clock signal with a temperature compensated circuit and a Crystal unit with good performance over a wide temperature range. Search by specifications Discontinued Products Information.
Here is a book that answers the need for a thorough, up-to-the-minute, practical guide to crystal oscillators for designers of oscillator circuits. It shows how to.
crystal oscillator pdf
This review presents various ways of detection of different physical quantities based on the frequency change of oscillators using piezoelectric crystals. These are influenced by the reactance changes modifying their electrical characteristics. Reactance in series, in parallel, or a combination of reactances can impact the electrical crystal substitute model by influencing its resonant oscillation frequency. In this way, various physical quantities near resonance can be detected with great sensitivity through a small change of capacitance or inductance.
Youcanview an example of sucha circuit below. PDF format. PDF with derivation of equation; Crystal. Quartz Crystal resonators will be discussed in more details later. It has High frequency of operation.
An engineer's introduction to concepts, algorithms, and advancements in Digital Signal Processing. This lucidly written resource makes extensive use of real-world examples as it covers all the important design and engineering references. Basic Oscillator Theory.
Data obtained by precision measurements of voltages on varicap diodes for the same oscillator frequencies over the operating temperature range are used for calculating values of the NTC thermistors and resistors. The method of realisation of TCXOs in thick film hybrid technology was developed and verified on prototypes. From these data the values of resistors and NTC thermistors were calculated.
Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions. A Study of Temperature Compensated Crystal Oscillator Based on Stress Processing Abstract: The most temperature compensated crystal oscillators must use compensation circuits and always based on fundamental crystals. We combine the different characteristics of quartz crystal including frequency-temperature characteristics and frequency-stress characteristics, with the influence of stress on the frequency of crystal blank to compensate the temperature influence on the frequency of crystal.
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