Colpitts Oscillator Design TheoryEtd Design Technique for Analog Temperature Compensation of Crystal Oscillators Mark A.Haney Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Electrical Engineering Dr.Dennis G.Sweeney Dr.Charles W.Bostian Dr. Ira Jacobs Blacksburg, Virginia Keywords: TCXO, Temperature Compensation, Crystal Oscillator Copyright 2001, Mark Haney Abstract For decades, the quartz crystal has been used for precise frequency control. In the increasingly popular field of wireless communications, available frequency spectrum is becoming very limited, and therefore regulatory agencies have imposed tight frequency stability requirements. There are generally two techniques for controlling the stability of a crystal oscillator with temperature variations of the environment. They are temperature control and temperature compensation. Temperature control involves placing the sensitive components of an oscillator in a temperature stable chamber. Usually referred to as an ovencontrolled crystal oscillator (OCXO), this technique can achieve very good stability over wide temperature ranges. Nevertheless, its use in miniature battery powered electronic devices is significantly limited by drawbacks such as cost, power consumption, and size. Temperature compensation, on the other hand, entails using temperature dependent circuit elements to compensate for shifts in frequency due to changes in ambient temperature. A crystal oscillator that uses this frequency stabilization technique is referred to as a temperaturecompensated crystal oscillator (TCXO). With little added cost, size, and power consumption, a TCXO is well suited for use in portable devices. This paper presents the theory of temperature compensation, and a procedure for designing a TCXO and predicting its performance over temperature. The equivalent electrical circuit model and frequency stability characteristics for the ATcut quartz crystal are developed. An oscillator circuit topology is introduced such that the crystal is operated in parallel resonance with an external capacitance, and equations are derived that express the frequency stability of the crystal oscillator as a function of the crystal’s capacitive load. This relationship leads to the development of the theory of temperature compensation by a crystal’s external load capacitance. An example of the TCXO design process is demonstrated with the aid of a MATLAB script Equivalent circuit of a quartz 2.2: Graph of a crystal’s reactance vs. 2.3: Typical frequencytemperature curves for ATcut 4.1: Network to measure crystal 5.1: Basic structure of Colpitts 5.2: Colpitts oscillator followed by a grounded collector PNP 5.3: Seriestoparallel 5.4: Complete TCXO 6.1: DC bias of the 6.2: Circuit used to measure frequencytemperature characteristic curve of 6.3: Cubic approximation for frequencytemperature data of 6.4: Graph of capacitive load required for compensation, , vs. 6.5: Schematic of 6.6: Comparison of total capacitance of the circuit () with required capacitance for compensation ()....41Figure 6.7: Predicted frequency error of TCXO 6.8: Schematic of the TCXO that was 6.9: Comparison of total capacitance () with required capacitance () for the TCXO circuit that was 6.10: Predicted frequency error of TCXO circuit that was 6.11: Experimental results of the TCXO frequency error over List of Equations Equation 2.1: Impedance of a quartz 2.2: Impedance of a quartz crystal in analysis friendly 2.3: Condition for 2.4: Solution for resonant frequencies of a quartz 2.5: Assumption used for simplification of resonant frequency 2.6: Approximate resonant frequency 2.7: Series resonant 2.8: Antiresonant 2.9: Approximation for antiresonant 2.10: Simplified approximation for antiresonant relationship of ATcut 3.1: Parallel resonant frequency of a crystal due to an external capacitive 3.2: Parallel resonant frequency expressed as a frequency offset from ..18Equation 3.3: Capacitive load expressed as a function of the frequency offset from ...19Equation 3.4: Total frequency offset from due to the capacitive load and change in 3.5: Capacitive load required for resonance at ...19Equation 3.6: Capacitive load required for resonance at in terms of the crystal’s motional and static capacitances, and it’s nominal capacitive 3.7: Total load capacitance required for temperature 4.1: Calculation for the motional resistance of a 4.2: Calculation for the motional capacitance of a 4.3: Calculation for the motional inductance of a 5.1: Expression for the capacitance of a negative temperature coefficient 5.2: Resistancetemperature relationship for an NTC 5.3: Series impedance of the thermistorcapacitor 5.4: Equivalent parallel impedance of the thermistorcapacitor 5.5: Expression for equivalent paral Tags: colpitts oscillator design theory,1 transistor oscillator circuits,single transistor oscillator,hartley oscillator multisim,colpitts oscillator theory,hartley oscillator circuit diagram,hartley oscillator applications,hartley oscillator calculator,hartley oscillator animation 
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