Telephone ring generator with automatic volume control according to the ambient noise level.

0001The invention relates to a telephone comprising means for generating a ringing tone upon detection of an incoming call, and means for controlling the volume of the ringing tone.

0002Current telephones, in particular cellular radio telephones, generally have the possibility of controlling the volume of the ringing tone which is generated when there is an incoming call so that it can be adjusted to be discernible above the noise level of the environment. In order to have the ringing tone reliably noticed, the ringing tone volume, in some cases, is arranged to increase at each ringing tone period so that the initial ring can be adjusted to a fixed level, and whereby the control logic of the telephone increases the volume level of subsequent rings.

0003In practice this kind of sound level control is not appropriate in all instances. For example, when a telephone is used in a car, if the initial level of the ringing sound is chosen high so as to be audible over the engine noise when the car is being driven hard then the ringing sound will probably be intrusive, even on the initial ring, when the car engine is idling. On the other hand, if the initial volume level is set low, it may take too long, from the system point of view, before the user will notice that the telephone is ringing in a noisy environment. At worst there might be not time to answer the call.

0004In another example, where a handheld cellular radio telephone or a pocket<img file="EP0507482A2_D0001.tif" />phone is carried in a silent environment, a loud ringing sound may give rise to awkward situations when it may startle other persons in addition to the person carrying the telephone.

0005The present invention aims to solve this problem by providing a telephone which further comprises, means for detecting the level of ambient noise signal and for producing a detection signal in response thereto, and wherein the ringing tone volume controlling means is operable, in response to the control signal, to vary the ringing tone volume. This has the advantage that there is generated a telephone ringing tone, whose volume is adjusted essentially to the noise level of the environment, so that the ringing sound at a given time is sufficiently strong to indicate an incoming call to the user, but sufficiently silent so that it will not cause a disturbance.

0006Preferably the ambient noise level is measured before the ringing sound is triggered. This has the advantage that the level of the ringing sound is directly related to the noise level of the environment.

0007The invention will be described, by way of example only, with reference to the accompanying drawings, of which: <ul id="ul0001" list-style="none"><li>Fig. 1 is a block diagram of a circuit embodying the invention, and</li><li>Fig. 2 is a circuit diagram corresponding to blocks 2 to 5 of Figure 1.</li></ul>

0008A cellular radio telephone typically comprises a transceiver coupled to an external antenna and all the other functions conventionally found in a mobile cellular telephone. Since these aspects of the telephone are not directly relevant to the instant invention no further details will be given here, except to say that a microprocessor is employed to control all the basic functions of the telephone.

0009As is also conventional, the telephone comprises an earpiece including a speaker, and a mouthpiece including a microphone.

0010The strength of an ambient noise signal input via a microphone 1, for example the microphone of the telephone mouthpiece, which has been amplified in an amplifier 2, and filtered in a filter 3 is detected in the demodulator (or detection circuit) 4. Upon further filtering in a low-pass filter 5, a detection signal from the demodulator 4, having a value representing the measured ambient noise signal strength, is supplied via an analog to digital converter (ADC) (not shown), to the telephone's control logic, which in present car and mobile telephones usually is a microprocessor 6 provided with a memory as discussed above. The processor 6 compares the obtained environmental sound or noise level i.e the ambient noise signal strength as represented by the detection signal, with reference values stored in a table in the memory. For each reference value, an empirically obtained suitable control signal value is also stored into the memory. The part of the microprocessor 6 controlling the ringing tone volume supplies a control signal having a value obtained from the table in the memory, via an amplifier 7 to a loudspeaker or buzzer 8 to trigger a ringing tone of a volume suitably adapted to the environment. The loudspeaker 8 may be the loudspeaker of the telephone earpiece.

0011The filter 3 may be a so called sofometric filter having a frequency range of about 300-4000 Hz.

0012Several samples can be taken of the detection signal and an average value generated from them, so that it is possible to prevent inappropriate ringing tone volumes being generated due to occasional transient sound peaks or silent moments in the environment.

0013As shown in Fig. 2, the amplifier 2 and the filter 3 are constituted by an operational amplifier and the input branch and feedback loops thereof. The demodulator 4 is simply a pair of diodes D1 and D2 and the low pass filter 5 is constituted by resistors R5, R6 and R7 and capacitors C2, C3.

0014The ambient noise level is measured at least when a new call is received by the telephone, before the first ringing sound is triggered.

0015Typical component values are:- <dl id="dl0001"><dt>C1,C2 and C3</dt><dd>= 0.1µF</dd><dt>C</dt><dd>= 270pF</dd><dt>R1</dt><dd>= 82kΩ</dd><dt>R2 and R3</dt><dd>= 47kΩ</dd><dt>R4</dt><dd>= 10kΩ</dd><dt>R5 and R7</dt><dd>= 220kΩ</dd><dt>R6</dt><dd>= 100kΩ</dd></dl>

0016Diodes D1 and D2 can be any diode for example 1N 4148.

0017Alternatively it is possible to perform the measurement before each ringing tone, or at the beginning of each ringing tone period before the ringing tone is generated. The length of the ringing tone period generally varies between 3 and 7 seconds, and before the call is answered there may be 3 to 10 rings, covering a time period of even more than 30 seconds.

0018It is a preferred practice to control the volume level of each ringing tone individually when the telephone is used in an environment where the ambient noise level can vary considerably during a relatively short period of time.

0019In some cases mobile telephones are used in environmental conditions in which the ambient noise levels are very difficult to assess. As an example of this is a pocket telephone which is alternately kept on the table and in the pocket. In this case, it is preferable to arrange a measurement of the ambient noise level during an idle state, say at regular intervals, i.e. the ambient noise level is measured when the telephone is in the idle state, waiting for an incoming call. The volume level of the ambient noise in the idle state is stored as an idle state noise value in the memory of the microprocessor 6. It is then possible to modify the control signal value with this idle state noise value or with the average value of several idle state noise values. In this way it is possible to better take into account the average noise level of the environment and to adjust the ringing sound to the environment.

0020In view of the foregoing description it will be obvious to a person skilled in the art that various modifications may be made within the scope of the present invention.