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Über dieses Buch

Electronic oscillators using an electromechanical device as a frequency reference are irreplaceable components of systems-on-chip for time-keeping, carrier frequency generation and digital clock generation. With their excellent frequency stability and very large quality factor Q, quartz crystal resonators have been the dominant solution for more than 70 years. But new possibilities are now offered by micro-electro-mechanical (MEM) resonators, that have a qualitatively identical equivalent electrical circuit.

Low-Power Crystal and MEMS Oscillators concentrates on the analysis and design of the most important schemes of integrated oscillator circuits. It explains how these circuits can be optimized by best exploiting the very high Q of the resonator to achieve the minimum power consumption compatible with the requirements on frequency stability and phase noise. The author has 40 years of experience in designing very low-power, high-performance quartz oscillators for watches and other battery operated systems and has accumulated most of the material during this period. Some additional original material related to phase noise has been added. The explanations are mainly supported by analytical developments, whereas computer simulation is limited to numerical examples. The main part is dedicated to the most important Pierce circuit, with a full design procedure illustrated by examples. Symmetrical circuits that became popular for modern telecommunication systems are analyzed in a last chapter.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
Relevant time durations for modern science range from the femtosecond of very fast electronics to the age of the universe, 15 billion years. This corresponds to a range of about 32 orders of magnitude. Moreover, this variable can be controlled and measured with an accuracy better than 10−14 by modern atomic clocks. However, the accuracy that can be obtained by purely electronic circuits, such as integrated circuits, is only of the order of 10−3. This is because there is no combination of available electronic components (like a RC time constant for example) that is more precise and constant with time and temperature. Now, 10−3 corresponds to an error of about 1.5 minute per day, which is totally unacceptable for timekeeping applications. The same is true for applications to modern telecommunications, which exploits the frequency spectrum up to 300Ghz.
Eric Vittoz

Chapter 2. Quartz and MEM Resonators

Abstract
As illustrated by Fig. 2.1(a), a quartz resonator is essentially a capacitor, the dielectric of which is silicon dioxide (SiO2), the same chemical compound as used in integrated circuits. However, instead of being a glass, it is a monocrystal, a quartz crystal, which exhibits piezoelectric properties. Therefore, a part of the electrical energy stored in the capacitor is converted into mechanical energy.
Eric Vittoz

Chapter 3. General Theory of High-Q Oscillators

Abstract
In order to sustain the oscillation of the resonator, it must be combined with a circuit to form a full oscillator, as illustrated in Fig. 3.1(a).
Eric Vittoz

Chapter 4. Theory of the Pierce Oscillator

Abstract
The simplest possible oscillator uses a single active device to generate the required negative resistance. If no inductance is available, the only possibility is the 3-point oscillator developed in 1923 by G. W. Pierce [2, 3]. The principle of this oscillator is depicted in Fig. 4.1. The active device is assumed to be a MOS transistor, but it could be a bipolar transistor as well. The source of the MOS transistor is connected to its substrate, to make it a 3-terminal device. The bias circuitry needed to activate the transistor is omitted here. Capacitors C 1 and C 2 connected between gate and source, respectively drain and source, are functional: they must have finite values in order to obtain a negative resistance across the motional impedance of the resonator.
Eric Vittoz

Chapter 5. Implementations of the Pierce Oscillator

Abstract
Grounding the source of the active transistor results in the basic oscillator circuit depicted in Fig. 5.1. Transistor T2 is part of a current mirror that delivers the bias current I 0 to the active transistor T1. The latter is maintained in active mode by a resistor R 3 that forces the DC component V D0 of the drain voltage V D to be equal to the DC component V G0 of the gate voltage V G (since no current is flowing through R 3).
Eric Vittoz

Chapter 6. Alternative Architectures

Abstract
The basic 3-point Pierce oscillator of Fig. 4.1 is the only possible configuration of a quartz (or MEMS) oscillator using a single active transistor. As soon as two or more active transistors are considered, many configurations become possible. Three of them will be discussed in this last Chapter.
Eric Vittoz

Backmatter

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