Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
2000-03-06
2001-01-30
Grimm, Siegfried H. (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S158000, C331S179000
Reexamination Certificate
active
06181215
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of electronics. More specifically, the invention relates to an oscillator circuit having a quartz resonator.
U.S. Pat. No. 5,117,206 (see equivalent EP 0 431 887 A2); U.S. Pat. No. 5,446,420 (EP 0 641 080 A2); and U.S. Pat. No. 4,941,156 describe oscillator circuits which include, between a first and a second circuit node, a parallel circuit of a quartz resonator, an inverter and a resistor element. The circuit nodes are each connected to ground via at least one capacitor. At least one of the circuit nodes has a parallel circuit of a sizable number of capacitors which can be switched in or off by means of switches. The frequency of the oscillator circuit can be set in this way.
When the capacitors are switched in or off at arbitrary instants during the operation of the oscillator circuit, the oscillation generated is subjected to an unpredictable influence at the switching instant because of the sudden change in the total capacitance at the respective circuit node.
SUMMARY OF THE INVENTION
The object of the invention is to provide an oscillator circuit with an oscillator quartz which overcomes the above noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which automatically sets the switching instant for switching in or switching off the capacitors so that the behavior of the oscillator circuit can be calculated in advance very well.
With the above and other objects in view there is provided, in accordance with the invention, an oscillator circuit, comprising:
a first circuit node and a second circuit node;
a parallel circuit including a quartz resonator, a first inverter, and a first resistor element connected in parallel between the first and second circuit nodes;
a first capacitor circuit connected between the first circuit node and a reference potential;
a second capacitor circuit connected between the second circuit node and the reference potential;
the first capacitor circuit having at least two capacitors each with a first terminal connected to the reference potential and a second terminal;
switching elements respectively connected between each of the second terminals of the at least two capacitors and the first circuit node; and
a synchronizing circuit connected to the switching elements, the synchronizing circuit generating a synchronizing signal for switching at least one of the switching elements in dependence on a potential at the first circuit node.
In other words, the oscillator circuit has, between the first and the second circuit node, a parallel circuit of a quartz resonator, a first inverter, and a first resistor element. The first circuit node is connected to a reference potential via a first capacitor circuit, and the second circuit node is connected to a reference potential via a second capacitor circuit. The first capacitor circuit has at least two capacitors with a first and a second terminal each, whose first terminal is connected to the reference potential and whose second terminal is connected to the first circuit node via one switching element each. Moreover, it is provided that the oscillator circuit has a synchronizing circuit for generating a synchronizing signal, which triggers switching of at least one of the switching elements of the first capacitor circuit as a function of a potential at the first circuit node.
In the novel circuit, the frequency is set by actuating the switching elements, as a result of which a different number of the capacitors of the first capacitor circuit are connected in parallel with one another between the first circuit node and the reference potential. The synchronization has the advantage that during the operation of the oscillator circuit it is possible to carry out a change in the operating frequency by switching the switching elements at an instant which is determined by the oscillatory characteristics of the oscillator circuit itself. Thus, the behavior of the oscillator circuit before and after switching of at least one of the switching elements during operation can be calculated in advance very well.
In accordance with an added feature of the invention, the oscillator circuit further comprises:
a third circuit node;
each of the switching elements having a first switching state wherein the switching element connects the second terminal of a respective the capacitor to the first circuit node, and a second switching state wherein the switching element connects the second terminal to the third circuit node; and
a precharging circuit connected to the third circuit node for generating a precharging potential.
In this development of the invention, therefore, the oscillator circuit has a precharging circuit in addition to the synchronizing circuit. The precharging circuit generates a precharging potential. The precharging circuit has the advantage that the capacitors of the first capacitor circuit, whose switching elements are in the second switching state, are precharged to a defined precharging potential, with the result that in the case of switching in the capacitors during operation of the oscillator circuit, that is to say in the case of a change in frequency, the potential at the first circuit node is influenced in a predictable way essentially by the fixed precharging potential.
In accordance with an additional feature of the invention, the synchronizing circuit triggers a switching of at least one of the switching elements from the second switching state into the first switching state whenever a potential at the first circuit node essentially corresponds to the precharging potential at the third circuit node.
This embodiment is particularly advantageous where the synchronizing circuit triggers switching of the switching elements precisely when the potential at the first circuit node corresponds essentially to the precharging potential at the third circuit node to which the capacitors of the first capacitor circuit which are connected thereto are precharged. Upon switching in further capacitors at the first circuit node, there is then no sort of influence on the potential at the first circuit node. As a result, the oscillatory characteristics of the oscillator circuit are virtually interference-free even in the case of changes in frequency carried out during operation.
In order to carry out the comparison between the potential at the first circuit node and the precharging potential, the synchronizing circuit can, for example, have an appropriate comparator. A simpler and very advantageous form of implementation of the synchronizing circuit is explained further below with the aid of the exemplary embodiment.
In accordance with another feature of the invention, the first inverter has a transistor of a first conductivity type and a transistor of a second conductivity type;
the precharging circuit has a second inverter with a transistor of the first conductivity type and with a transistor of the second conductivity type, and a second resistor element connected in parallel with the second inverter, one of an input and an output of the second inverter being connected to the third circuit node;
a quotient of a width-to-length ratio of the transistor of the first conductivity type to a width-to-length ratio of the transistor of the second conductivity type is substantially equal in the first inverter and in the second inverter.
In accordance with a further feature of the invention, the first inverter and the second inverter are CMOS inverters.
In accordance with again another feature of the invention, the first inverter has a transistor of a first conductivity type and a transistor of a second conductivity type;
the synchronizing circuit has a third inverter with a transistor of the first conductivity type, a transistor of the second conductivity type, an input connected to the first circuit node, and an output for outputting a synchronizing signal; and
a quotient of a width-to-length ratio of the transistor of the first conductivity type to a width-to-length ratio of the transistor of the second c
Greeberg Laurence A.
Grimm Siegfried H.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
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