Oscillators – Solid state active element oscillator – Transistors
Patent
1997-11-14
1999-06-15
Mis, David
Oscillators
Solid state active element oscillator
Transistors
331117R, 331158, 331177V, 331 60, H03B 536, H03B 512
Patent
active
059125942
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an oscillator comprising a (first) amplifier element which has a control terminal and a main current path ending in a first and a second output terminal, the oscillator including a network through which the first output terminal of the (first) amplifier element is fed back to the control terminal of the (first) amplifier element by a series-arranged piezoelectric oscillation element, and including a (first) output dipole (i.e., a reactive circuit element, such as a resonant LC circuit or inductor); coupled to the first output terminal of the (first) amplifier element and including a DC current defining element coupled to the second output terminal of the (first) amplifier element. For simplicity, a reactive circuit element will be referred to hereinafter and in the claims as a dipole. A dipole shall be understood to mean a dipolar electrical energy storage element, such as a capacitive, inductive or resonant LC circuit element.
From the monograph "Oscillator Design Handbook" by Gary A. Breed, published 1990 by Cardiff Publishing Company, more particularly pp. 55 to 60, crystal oscillators of various types are known. A so called "Pierce oscillator" has in its simplest embodiment an npn transistor as an amplifier element, whose collector and base are coupled to each other via a crystal (quartz crystal). The collector is furthermore connected via an inductor to a positive supply voltage terminal and represents the output of the "Pierce oscillator". Furthermore are connected to ground the collector of the transistor, via a first capacitor which may be tunable, the base, via a second capacitor and the emitter of the transistor via the parallel circuit of an emitter resistor having a very large capacitance. The base is further connected to the positive supply voltage terminal via a dropping resistor. In a modification, a parallel resonant circuit having an inductor and a--tunably arranged--capacitor capacitor may take the place of the inductor at the collector. This antiresonant circuit can be tuned to the oscillation frequency of the crystal.
This "Pierce oscillator" is designated as having the best frequency stability of all the crystal oscillators discussed in the "Oscillator Design Handbook" it is true, but for a miniaturized integration on a semiconductor body, the very large capacitor in the emitter circuit i.e. between emitter and ground, is highly annoying, because it takes up an unproportionally large space on the semiconductor body. This forms a large hindrance as to the construction, especially for small, light electronic devices such as, for example, radio pagers (pagers).
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide an oscillator, more particularly a so-called "Pierce oscillator" of the design described above, in the way that the described very large capacitor may be omitted.
This object is achieved in an oscillator according to the invention by a second amplifier element which has a main current path ending in a (second) output terminal, this (second) output terminal of the second amplifier element being coupled to the second output terminal of the first amplifier element.
As against the state-of-the-art "Pierce oscillator", the very large capacitor in the oscillator according to the invention, which capacitor is to form a short-circuit to ground for the frequency of the oscillator, is replaced by the impedance of the (second) output terminal of the second amplifier element. This impedance can be set to a low-ohmic value with simple technical measures for the frequency of the oscillator, so that with the oscillator arrangement according to the invention at least substantially a high frequency short-circuit is achieved on the second output terminal of the first amplifier element. This high frequency short-circuit provides that the element defining the DC current is bypassed, which element is connected to the second output terminal and is high-ohmic for the frequency of the oscillator. In the state of the art
REFERENCES:
patent: 5113153 (1992-05-01), Soyuer
patent: 5166645 (1992-11-01), Watts
"Oscillator Design Handbook" by Gary A. Breed, published 1990 by Cardiff Publishing Company pp. 55-60.
Mis David
Slobod Jack D.
U.S. Philips Corporation
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