Oscillators – Relaxation oscillators
Reexamination Certificate
1999-11-05
2001-05-01
Mis, David (Department: 2817)
Oscillators
Relaxation oscillators
C331S1160FE, C331S144000, C331S145000, C331S151000, C331S158000
Reexamination Certificate
active
06225872
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a resonator having a resonating device and a selection circuit for selecting a resonance mode, the selection circuit being formed by a first-order oscillator.
DESCRIPTION OF THE RELATED ART
In standard electronic systems, resonator oscillators are designed by using the known negative impedance structure, such as is described, for example, in the PhD thesis entitled “Design of High-Performance Negative-Feedback Oscillators” by C.A.M. Boon published in the Delft University of Technology in 1989 and in the article entitled “Low-Noise Oscillators” by J. H. Huijsing et al. published in “Analog Circuit Design” by Kluwer Academic Publishers in 1996.
In generally known resonators, a desired resonance mode is selected by means of a tuned circuit.
The resonators used hitherto have the disadvantage that resonant circuits are expensive and fragile compared with other components in an electronic circuit and, in addition, are difficult to integrate with the desired requirements.
From Patents Abstract of Japan, vol. 4, no. 18 (E-171), Feb. 13, 1980 & Japan 54 157461 A, Dec. 12, 1979 a resonator provided with a resonating device in form of a piezoelectric element is known. A resonance mode is selected by using a monostable multivibrator, of which the pulse direction is selected. Said multivibrator is not a first-order oscillator, whereas the type of selection is completely different from that of the resonator of this invention. Moreover, in the prior art resonator it is only aimed to secure the minimum natural oscillation number of the piezoelectric element and not an overtone mode.
The U.S. Pat. No. 3,581,235 discloses a resonator comprising a crystal and an stable multivibrator consisting of two transistors with resistive cross-coupling. By this kind of cross-coupling the crystal has an impedance influence on the stable multivibrator in contrast to the threshold influence in the resonator according to the invention.
SUMMARY OF THE INVENTION
The object of the invention is to provide a resonator of the type mentioned in the preamble which is improved with respect to known resonators, the abovementioned disadvantages being eliminated and the problem of subordinate resonances and that of direct breakthrough being avoided, while it is readily possible to excite resonators in a higher mode.
This object is achieved, according to the invention in that the oscillator comprises a capacitor and a switchable current source which is connected thereto by a control input for the alternating charging and discharging of said capacitor, and two comparators, first inputs of which are connected to the connection point of the capacitor and the switchable current source, other inputs of which are each connected to a reference source, and the output of which is connected to a memory circuit whose output signal is at a first level if the one comparator delivers an output signal and is at a second level if the second comparator delivers an output signal, wherein the output of the memory circuit is connected to the input of the resonating device and the control input of the switchable current source and wherein the output signal of the resonating device modulates the reference sources.
The different operation of the known resonator with respect to the resonator according to present invention appears from the requirement that the natural frequency of the multivibrator must be slightly higher than the resonant frequency of the crystal, whereas that of the first-order oscillator of present invention must only be nearly equal to the resonant frequency of the crystal, i.e. both slightly higher or slightly lower than said resonant frequency or a higher harmonic thereof.
The natural frequency of the first-order oscillator may be chosen as almost equal to the desired frequency of the output signal of the resonator. When synchronization is reached, the frequency generated is ultimately completely determined by the resonating device.
Choosing the natural frequency of the first-order oscillator by means of its frequency-determining components enables the range to be set in which synchronization is maintained. In this way, any subordinated resonance of the resonator can be selected.
In one embodiment, an amplifier is incorporated between the output of the resonating device and the reference sources of the first-order oscillator in order to obtain a synchronization sensitivity of the oscillator which is such that it reliably resonates as an entity at a desired frequency.
Preferably, the output signal of the first-order oscillator is a square wave. Further elaborations of the invention are described in the subsequent claims.
REFERENCES:
patent: 3581235 (1971-05-01), Siu
patent: 3961284 (1976-06-01), Flora
patent: 20 65 090 (1972-04-01), None
patent: 54-157461 (1979-12-01), None
R. Hofer, “Schnelle Komparatoren Sinnvoll Eingesetzt”,Elektronik, vol. 35, No. 12, Jun. 1986, pp. 76-78.
Mis David
Technische Universiteit Delft
Young & Thompson
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