Oscillators – Bridge type – R.c. or r.l. type
Reexamination Certificate
2000-01-19
2001-10-09
Lam, Tuan T. (Department: 2816)
Oscillators
Bridge type
R.c. or r.l. type
C331S110000
Reexamination Certificate
active
06300844
ABSTRACT:
This application claims priority under 35 U.S.C. §119 and/or 365 to 9900156-2 filed in Sweden on Jan. 20, 1999; the entire content of which is hereby incorporated by reference.
FIELD OF INVENTION
The present invention relates to a method of quick-starting a sinewave oscillator, and to a sinewave oscillator quick-start device according to respective preambles of claims
1
and
6
.
DESCRIPTION OF THE BACKGROUND ART
For the purpose of generating an analog telephone ringing signal, there is required a sinewave signal that has a low frequency in the range of 16-60 Hz. In the ringing mode, the actual ringing signal is generated between about 20% and 50% of the time, depending on each individual specification. For instance, a ringing signal will sound for one second, followed by three seconds of silence. In the case of certain short line applications?, where only one to two, or more, analog lines are found, for instance ISDN, some manufacturers use a calling subscriber line circuit referred to as a Subscriber Line Interface Circuit (SLIC). This circuit sends a ringing signal to a telephone, without the use of an external ringing generator and ringing relay. In this construction, the SLIC functions as a path amplifier which is supplied with a sinus signal. The ringing signal is generated by some form of oscillator, e.g. a “Wiener bridge oscillator”.
The risk of interference can be reduced and the power consumption of the SLIC kept low when the SLIC is not in a ringing Tnode, by switching-off the oscillator and then starting the oscillator when necessary. Unfortunately, this cannot always be easily achieved since the time lapse from the moment of applying the voltage to the moment at which the sinewave ringing signal is fully developed is very long in comparison with the period time of the ringing signal in the case of that type of precision oscillator which is required to fulfil the requirement of producing a ringing signal of low distortion. It is necessary to start the oscillator at least one second before a fully developed output signal has been obtained, which renders this solution unrealistic in practice. The start time can be shortened, although at the cost of increased distortion—meaning that it is unrealistic in practice.
BACKGROUND OF THE INVENTION
The present invention addresses the problem of how a telephone circuit can be caused to operate with low power consumption in parallel with enabling a sinewave ringing signal to be generated very quickly.
Accordingly, the object of the present invention is to construct an oscillator with which a sinewave ringing signal can be quickly generated, so as to achieve low power consumption and low distortion in a telephone circuit.
The aforesaid problem is solved by the present invention as characterised in the characterising clauses of respective claims
1
and
6
.
A quick-start ringing signal can be obtained in an SLIC, by forward biasing one of the connections of the amplifier (output, negative or positive inputs) when no ringing signal is required. This can be achieved, among other things, by disconnecting one of the supply voltages. In the ringing mode, the disconnected supply voltage is reconnected and the oscillator starts when the amplifier begins to work and drives the output to earth.
According to one preferred embodiment an inventive device for generating the sinewave output signal and including an oscillator in accordance with the invention comprises means for engaging and disengaging one of the supply voltages of said device so that the sinewave output signal will be stabilised when connecting said supply voltage after a time period corresponding to an interval of 1-5 periods of the sinewave output signal.
One advantage afforded by the invention is that the sinewave ringing signal from the oscillator can be generated quickly without needing to pre-start the oscillator in order to achieve the desired output signal.
Another advantage afforded by the invention is that the telephone circuit has a lower power consumption when the oscillator is switched-off when not in use.
Another advantage resides in the elimination of an unnecessary noise source, which has its origin in the oscillator, because the oscillator is switched-off when not in use.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.
REFERENCES:
patent: 4286233 (1981-08-01), Kucharewski et al.
patent: 4558309 (1985-12-01), Antonewich
patent: 4833427 (1989-05-01), Leuthold et al.
patent: 5277495 (1994-01-01), Forehand
patent: 5870000 (1999-02-01), Matsuda et al.
patent: 6072340 (2000-06-01), Deisch
patent: 06120732 (1994-04-01), None
patent: 10290119 (1998-10-01), None
Burns Doane Swecker & Mathis L.L.P.
Lam Tuan T.
Telefonaktiebolaget LM Ericsson (publ)
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