FI97512C - Generating a ringtone - Google Patents

Description

97512

Ring signal generation

The invention relates to a method according to the preamble of appended claim 1 and to an arrangement according to the preamble of appended claim 2 for generating a ringing signal for a subscriber device. Such a method and arrangement generates the ringing signal with which the alarm of the subscriber unit (e.g., the AC power coil of the telephone) is called.

The purpose of the ring generator is to generate the voltage required to sound the alarm on the telephone set, which is defined in international standards as 70 Vrmg (100 V Peak-to-Peak) and 25 Hz. Such a sinusoidal voltage is shown in Figure 1. Some telephone exchanges may also use a ringing voltage frequency of 50 Hz. The ring-activated alarm is typically an AC telephone bell or a conventional alarm used in the latest telephones instead of a standard (mechanical) bell.

In known solutions, the call generator is placed in a local exchange or a subscriber multiplexer (the subscriber multiplexer is a multiplexer as close as possible to the subscribers, connecting several subscribers to the local exchange) according to the principle shown in Figure 2, i.e. common to a multi-subscriber telephone device SD1 ... SDN. The subscriber interface circuit SC1 ... SCN of each subscriber has a relay RL, with which a ringing signal is connected to the subscriber device via the subscriber line SUBL, if necessary. Figure 2 shows a ringing signal connected to the subscriber device SD2 from the common generator RG while the other subscriber devices are connected to the voice path VP.

The call generator RG may be, for example, a device as shown in Fig. 3 35, comprising a power supply 31, 297512 an oscillator 32 and an amplifier 33. The power supply provides the operating voltages required by the oscillator and the amplifier, which in the example case are + 12V and -12V and + 55V and -55V. The power supply can be, for example, a flyback-type 5-pin switch power supply. The oscillator 32 generates an AC voltage V of 25 Hz, which is amplified by the amplifier 33 to a call voltage V2 as shown in Fig. 1.

However, the ring generator is particularly associated with two drawbacks. First, the call generator is relatively expensive, so it contributes to the cost of the exchange or subscriber multiplexer. In addition, the ring generator is a large device that takes up space at its installation site. The latter drawback is particularly pronounced in subscriber multi-15 plexiglasses, which may have to be installed in confined spaces.

The object of the present invention is to overcome the above-mentioned drawbacks. This object is achieved by a method according to the present invention, characterized by what is described in the characterizing part of the appended claim 1. The arrangement according to the invention, in turn, is characterized by what is described in the characterizing part of the appended claim 2.

The idea of the invention is to make use of a known subscriber interface circuit (so-called SLIC circuit) and in particular its polarity switching feature, by using such a circuit by changing the polarity of the subscriber line in step with the ringing signal. In this way, the ringing voltage defined in the standards can be approximated with sufficient accuracy, but without the need for a ringing generator similar to that shown in Fig. 3.

Thanks to the solution according to the invention, the cumbersome ring generator is thus completely eliminated, but no additional components are required for the generation of the ring signal.

97512 3

The solution according to the invention is particularly suitable for subscriber multiplexers close to the subscriber, since no precise distortion requirements have been set for them with respect to the ringing voltage.

In the following, the invention and its preferred embodiments will be described in more detail with reference to Figs. 4 to 7 in the accompanying drawings, in which Fig. 1 shows a 15 is generated in accordance with the invention, Figure 5 illustrates the generation of a ringing signal in the apparatus shown in Figure 4, Figure 6 shows a ringing signal generated in accordance with the invention, and Figure 7 illustrates a preferred embodiment for the apparatus shown in Figure 5.

Figure 4 illustrates a subscriber multiplexer 40 in which a ringing signal is generated in accordance with the invention. (More specifically, the figure shows the subscriber-side end of a subscriber multiplexer 25 in which the solution according to the invention is used.) The subscriber multiplexer has several mutually similar subscriber interface circuits SUB, each of which is common to one or typically, however, several subscribers. Each subscriber line 30 is connected to a multiplexer / demultiplexer section 41, which performs multiplexing of data leaving the exchange and demultiplexing of data coming from the exchange. The data stream to and from the exchange may form, for example, a known basic channelization system (2048 kbit / s) with 30 voice channels in accordance with ITU-T (formerly 35 CCITT) recommendations (G.704).

At the exchange end, the 2048 kbit / s connection shown in Figure 4 can be connected either directly to the exchange's digital subscriber interface or via a separate adapter unit to the exchange's analog subscriber interfaces. In the case of an analog exchange, the required adapter unit comprises, corresponding to the subscriber's end, a multiplexer / demultiplexer section and central interface units, which on the one hand simulate the functions of the exchange to the subscriber and on the other hand transmit the analog subscriber loop signaling to the exchange.

In each of the subscriber interface circuits shown in Fig. 4, the subscriber interface of an individual subscriber is implemented as shown in Fig. 5.

The actual subscriber connection is implemented with a connection circuit known per se, the so-called With SLIC circuit 50 (Subscriber Line Interface Circuit). In practice, the SLIC circuit handles, for example, power supply and subscriber loop signaling. 20 Thus, the SLIC circuit recognizes the selections made by the subscriber, the operations of lifting the telephone handset, etc., and handles the signaling thereof. In practice, the SLIC also performs 2-wire / 4-wire conversion and is connected to the analog 4-wire interface of codec 51.

The codec 51 converts the digital signal from the exchange to an analog format and the analog signal to the exchange to a digital format, respectively. The SLIC circuit supplies the analog signal given to it by the codec to the 2-wire subscriber line SUBL together with the DC-30 current component (above-mentioned power supply). The SLIC circuit of the speech signal from the subscriber separates the signal received from the exchange from the signal and passes it on to the codes for the above-mentioned A / D conversion.

It is essential to the present invention that the 35 SLICs have a polarity reversal feature (polarity

II

5 97512 reversal), i.e. the SLIC circuit allows the polarity of the a and b conductors of the subscriber line SUBL to be reversed from the normal situation (where the polarity of the a-conductor is positive and the polarity of the b-conductor is negative).

5 An SLIC circuit as described above may be e.g.

one of the Am795XX or Am79M5XX series circuits, manufactured by Advanced Micro Devices, USA. Similar circuits are available from other manufacturers.

According to the present invention, the ability of the SLIC circuit to change the polarity of the subscriber lines is utilized in generating the ring signal. When a ringing signal needs to be generated for a subscriber, the SLIC circuit is controlled to change the polarity of the subscriber lines to the beat of the ringing signal. This means that the polarity 15 varies e.g. at intervals of about 20 ms (corresponding to a ringing voltage frequency of 25 Hz). Fig. 5 shows a control for performing continuous polarity reversal in step with the ringing signal by reference numeral 52. Such control of the SLIC circuit can be easily implemented e.g. by means of a microprocessor.

20 (For example, in the above-mentioned AMD circuits, control is via input decoder inputs C1-C3.)

Figure 6 shows a ringing signal generated in accordance with the invention. The rate of rise and fall of the voltage (i.e., the rate of change of polarity) can be set by the components (resistors and capacitors) associated with the SLIC circuit to a desired constant value so that the voltage shape is as close as possible to the sinusoidal shape. (For example, in the case of the above-mentioned circuit family, the setting is made with resistors RDC1 and RDC2 and with a capacitor CDC, as can be seen from the data sheets of the circuit family in question).

In a SLIC circuit, it is generally not desired to do a polarity reversal very abruptly because a sudden change generates interference to adjacent telephones. This is also advantageous for the present invention, because in this way the rope form is inherently closer to the sinusoid form. The peak value of the voltage • <6 97512 depends on the SLIC circuit used, typically being about ± 30V, which is practically quite a sufficient call voltage. (It is also possible to use additional amplifiers to increase the voltage value.) 5 A separate circuit can also be added to the SLIC circuit to make the ring voltage rise rate (i.e., polarity reversal rate) optional (a few rate values can be selected). Thus, in such a circuit, there are several different options for the above-mentioned components determining the polarity reversal rate, one of which is connected to the SLIC circuit at a time. This principle is illustrated in Figure 7, where circuits with different component values are denoted by reference numerals A, B and C. Of these, the SLIC circuit uses one at a time according to which of them has been selected for use by the selection means 53. (For clarity, Figure 7 shows these polarity reversal rate determining components as components outside the SLIC circuit, while Figure 5 assumes that one such component combination is included in the SLIC circuit 50.) As can be seen from the above, very few modifications are required to practice the present invention. known solutions. The only mandatory change concerns the control of the SLIC circuit, i.e. the polarity change is made continuous at the rate determined by the ringing signal. The information 25 that the ringing signal must be generated is obtained in a manner known per se.

Although the invention has been described above with reference to the examples according to the accompanying drawings, it is clear that the invention is not limited thereto, but can be modified within the scope of the inventive idea set forth above and in the appended claims. For example, the ringing voltage and its frequency can be changed depending on where and for which subscriber devices the ringing signal is generated.

• «

Claims (3)

97512 A method for generating a ringing signal for a subscriber unit (SD1 ... SDN), characterized in that the generation is performed by a subscriber interface circuit (50) with a polarity switching feature known per se by changing the polarity supplied by such a circuit to the subscriber line at a clock rate. 2. An arrangement for generating a ringing signal for a subscriber device (SD1 ... SDN), such as a telephone, according to which a subscriber line (SUBL) originating from a subscriber device is connected to a SLIC subscriber interface circuit (50) known per se, which is provided with a polarity switching feature. for reversing the polarity 15, characterized in that it comprises control means (52) for continuously changing the polarity supplied to the subscriber line by the SLIC circuit at a rate determined by the ringing signal to generate a ringing signal by said control means for the subscriber unit. An arrangement according to claim 2, characterized in that it comprises means (53, A, B, C) for changing the polarity reversal rate. 97512