Abstract:
A telephone comprises an acoustic alarm, conversation members, first control means for the acoustic alarm, second control means for the conversation members, first supply means and second supply means for absorbing energy from a telephone line, the first supply means and the second supply means supplying the first control means in a call condition and the second control means in a conversation condition, respectively, wherein the first supply means further supplying the second control means in the call condition.

Description:
TECHNICAL FIELD 
   The present invention relates to a telephone. 
   BACKGROUND OF THE INVENTION 
   A telephone is generally connected, by means of a telephone line, to an exchange which supplies the energy necessary to operate the telephone. In particular, the exchange constantly transmits a direct-current supply voltage on the telephone line. During a conversation, the direct-current voltage operates the various conversation members of the telephone such as, for example, a microphone and a loudspeaker, which are housed in a handset. On the other hand, when the telephone receives an incoming call, the exchange also transmits a corresponding sinusoidal signal on the telephone line; this call signal operates a buzzer which informs a user of the incoming call. 
   In a known passive telephone, there is a double switch operated by a fork-shaped hook for the handset. When the handset is resting on the fork-shaped hook, the switch connects the buzzer to the telephone line (in series with a decoupling capacitor); when the handset is lifted, the switch connects the conversation members to the telephone line. The call signal transmitted by the exchange on the telephone line thus rings the buzzer directly until the user lifts the handset in order to answer the call. 
   In a known electronic telephone, on the other hand, the buzzer and the conversation members are controlled by respective control units. When the telephone receives an incoming call, the signal transmitted by the exchange on the telephone line is used by an alternating-current/direct-current (AC/DC) converter to supply the control unit of the buzzer. When the user lifts the handset in order to answer the call, a switch operated by the fork-shaped hook connects a direct-current/direct-current (DC/DC) converter to the telephone line; this DC/DC converter supplies the control unit of the conversation members (whilst the AC/DC converter is automatically deactivated). 
   Each time the user lifts the handset in order to answer a call and thus activates the DC/DC converter, the control unit of the conversation members is subject to an abrupt transient phenomenon before reaching a steady operating state. During the transient phenomenon, electrical interference with components having frequencies within the acoustic band is produced and turns into annoying noises in the loudspeaker of the telephone. 
   In order to solve this problem, it has been proposed to use filters which reduce the effect of the electrical interference. These filters require the use of fairly bulky, discrete components which have to be disposed outside an integrated circuit in which the control unit of the conversation members is typically formed. 
   A further problem is that it is necessary to keep the duration of the transient phenomenon within a narrow limit to prevent annoying waiting times for the user. A known solution is to provide speed-up circuits for activating the DC/DC converter, which reduce the duration of the transient phenomenon. However, these speed-up circuits are quite complex and rather expensive. 
   With reference in particular to  FIG. 1 , this shows a fixed telephone  100  commonly used in private dwellings and in offices. The telephone  100  has a main body  105  made, for example, of plastics material. A handset  110  which houses a microphone and a loudspeaker is connected to the main body  105  by means of a flexible cable wound in a spiral. The handset  110  normally rests on a fork-shaped hook  115  which projects from a seat formed in the main body  105 . The telephone  100  also has a keypad  120  which is used for dialing a telephone number to be called. Within the main body  105  there is a buzzer  125  which communicates with the exterior through a perforated portion. A connector  130  (connected to the main body by means of a flexible cable) is used to connect the telephone  100  to a telephone socket (not shown in the drawing). 
   In a known telephone, as shown in  FIG. 2 , the connector has two terminals  130   a  and  130   b  which are connected to a telephone line  205 . The terminals  130   a ,  130   b  are connected to respective input terminals of a polarity conditioning circuit  210  typically formed by a bridge composed of diodes with low conduction thresholds or a bridge composed of MOS transistors; the polarity conditioning circuit  210  has a reference output terminal  215   g  and a supply output terminal  215   v.    
   The telephone includes a supply constituted basically by an alternating-current/direct-current (AC/DC) converter which absorbs energy from the telephone line  205 . The supply comprises an input section (AC/DC)  220  having a reference terminal connected to the terminal  215   g  and an input terminal connected to the terminal  215   v . The AC/DC input section  220  has an output terminal connected to an anode terminal of a diode D 1 . A cathode terminal of the diode D 1  is connected to a terminal of a capacitor C 1  the other terminal of which is connected to the reference terminal  215   g . A comparator block  225  receives as an input a signal which is present at the supply terminal  215   v ; the comparator block  225  outputs a call presence signal R_ON which is supplied to an enabling terminal of the AC/DC input section  220 . 
   The supply  220 , D 1 , C 1  described above supplies a control unit (CTRL)  230  of the buzzer  125 . The control unit  230  has a reference terminal and a supply terminal which are connected, respectively, to the terminal  215   g  and to the cathode terminal of the diode D 1 . The control unit  230  also receives, at its own enabling terminal, the call presence signal R_ON supplied by the comparator block  225 . The control unit  230  has two output terminals which are connected to respective terminals of the buzzer  125 . 
   The telephone has a further supply (which absorbs energy from the telephone line  205 ), constituted substantially by a direct-current/direct-current (DC/DC) converter. This supply includes an input section (DC/DC)  240  having a reference terminal connected to the terminal  215   g  and an input terminal connected to the terminal  215   v  by means of a switch  245  operated by the fork-shaped hook  115  on which the handset  110  rests. The DC/DC input section  240  has an output terminal connected to an anode terminal of a diode D 2 . A cathode terminal of the diode D 2  is connected to a terminal of a capacitor C 2  the other terminal of which is connected to the reference terminal  215 g. 
   The further supply  240 , D 2 , C 2  described above supplies a control unit (CTRL)  250  for the microphone and the loudspeaker which are housed in the handset  110 . The control unit  250  has a reference terminal and a supply terminal which are connected, respectively, to the terminal  215   g  and to the cathode terminal of the diode D 2 . The control unit  250  has two output terminals which are connected to respective terminals of the handset  110 . 
   The telephone constantly receives a direct-current supply voltage from the telephone line  205 . For example, a battery disposed in a telephone exchange supplies to the telephone line  205  a supply voltage equal to 48V; because of the voltage drop in the telephone line  205  (which has a length of up to a few km), a supply voltage of the order of 4-10V (of positive or negative value according to the way in which the terminals  130   a ,  13 G b  are connected to the telephone line  205 ) is available at the terminals  130   a ,  130   b . The polarity conditioning circuit  210  ensures that a voltage of positive value relative to the reference terminal  215   g  (substantially equal to the absolute value of the voltage at the terminals  130   a ,  130   b  minus the voltage drops in the diodes of the bridge) is always available at the supply terminal  215   v.    
   In a rest condition, the call presence signal R_ON is deasserted so that the AC/DC input section  220  is deactivated. At the same time, the handset  110  is resting on the fork-shaped hook  115  and the switch  245  is therefore open. 
   When the telephone receives an incoming call, the exchange transmits on the telephone line  205  a sinusoidal call signal having, for example, a peak to peak amplitude of 250 V and a frequency of 100 Hz. The comparator block  225  detects the presence of the call signal and asserts the call presence signal R_ON. The AC/DC input section  220  is consequently activated and charges the capacitor C 1  to an internal supply voltage, for example, equal to 2.5-3V (the diode D 1  ensures that the capacitor C 1  cannot be discharged to the AC/DC input section  220 ). The voltage at the terminals of the capacitor C 1  supplies the control unit  230  (providing a relatively high power). The control unit  230  is activated by the call presence signal R_ON and therefore causes the buzzer  125  to ring. 
   As soon as a user lifts the handset  110  in order to answer the call, the fork-shaped hook  115  causes the switch  245  to close. The exchange notices a change in current absorption on the telephone line  205  by the telephone and therefore interrupts the call signal and establishes a connection with a calling telephone. The call presence signal R_ON is consequently deasserted so that the AC/DC input section  220  is deactivated. The DC/DC input section  240  charges the capacitor C 2  to the internal supply voltage (the diode D 2  ensures that the capacitor C 2  cannot be discharged to the DC/DC input section  240 ). This voltage at the terminals of the capacitor C 2  supplies the control unit  250  (supplying a fairly low power). This enables a conversation to be activated by the transmission, on the telephone line  205 , of a signal representative of voice data and having a limited peak to peak amplitude (for example of a few V) and a frequency within the acoustic band (200-3,400 Hz). 
   In some known telephones, the control unit  230  and the buzzer  125  are also used during conversation, for example, with a hands-free function. In this case, the DC/DC input section  240  also supplies the control unit  230  by means of a further diode and a further capacitor (not shown in the drawing). 
   Each time the DC/DC input section  240  is activated, the charging time of the capacitor C 2  gives rise to a transient phenomenon in the supply voltage of the control unit  250  with consequent electrical interference with components having frequencies within the acoustic band. To prevent this electrical interference from being translated into annoying noises in the loudspeaker housed in the handset  110  and to reduce the duration of the transient phenomenon, the telephone is provided, respectively, with filters and with speed-up circuits for charging the capacitor C 2  (not shown in the drawing). 
   SUMMARY OF THE INVENTION 
   An embodiment of the invention provides a telephone comprising an acoustic alarm, conversation members, first control means for the acoustic alarm, second control means for the conversation members, first supply means and second supply means for absorbing energy from a telephone line, the first supply means and second supply means supplying the first control means in a call condition and the second control means in a conversation condition, respectively, wherein the first supply means further supply the second control means in the call condition. 
   Moreover, the present invention also proposes a corresponding method of operating the telephone. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and the advantages of the telephone according to the present invention will become clear from the following description of a preferred embodiment thereof, given by way of non-limiting example, with reference to the appended drawings, in which: 
       FIG. 1  shows a telephone. 
       FIG. 2  is a basic block diagram of a known telephone. 
       FIG. 3  is a basic block diagram of a telephone according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference now to  FIG. 3 , this is a basic block diagram of a preferred embodiment of the present invention (elements corresponding to those shown in the previous drawing are identified by the same reference numerals and an explanation thereof is omitted to simplify the description). 
   In this telephone, the diodes connected to the output terminal of the AC/DC input section  220  and to the output terminal of the DC/DC input section  240  are replaced by respective transistors. In particular, there is a pnp bipolar transistor T 1  having an emitter terminal and a base terminal connected, respectively, to the input terminal and to the output terminal of the AC/DC input section  220 ; the transistor T 1  also has a collector terminal connected to a terminal of a capacitor C, the other terminal of which is connected to the reference terminal  215   g . Similarly, a pnp bipolar transistor T 2  has an emitter terminal connected to the input terminal of the DC/DC input section  240 , a base terminal connected to the output terminal of the DC/DC input section  240 , and a collector terminal connected to the collector terminal of the transistor T 1  (and therefore also to the capacitor C). 
   The telephone includes a further pnp bipolar transistor Ts associated with the DC/DC input section  240 . The transistor Ts has an emitter terminal connected to the input terminal of the DC/DC input section  240 , a base terminal connected, by means of an electronic switch  405 , to a further output terminal of the DC/DC input section  240 , and a collector terminal connected to the reference terminal  215   g . A comparator block  410  has two input terminals connected, respectively, to the emitter terminal and to the collector terminal of the transistor T 2 ; the comparator block outputs a signal for controlling the electronic switch  405 . 
   The control unit for the buzzer  125  and the control unit for the microphone and the loudspeaker housed in the handset  110  are formed in a single control device  415  integrated in a chip of semiconductor material. The control device  415  has a reference terminal connected to the terminal  215   g  and a supply terminal connected to the collectors of the transistors T 1  and T 2  (and hence to the capacitor C). 
   The control device  415  includes a block (CMN)  420  constituted by circuit elements common to both of the control units such as, for example, a biasing circuit. The common block  420  is connected to a control block (CTRL)  230   a  and a control block (CTRL)  250   a  corresponding, respectively, to the control unit for the buzzer  125  and to the control unit for the microphone and the loudspeaker housed in the handset  110  (apart from the common circuit elements of the block  420 ). The control block  230   a  and the control block  250   a  each have two output terminals which are connected, respectively, to the corresponding terminals of the buzzer  125  and of the handset  110 . 
   The control block  230   a  also receives, at its own enabling terminal, the call presence signal R_ON supplied by the comparator block  225 . The call presence signal R_ON is also supplied as an input to a NOT logic gate  425  which outputs a conversation presence signal C_ON; the conversation presence signal C_ON is supplied to an enabling terminal of the control block  250   a.    
   When the telephone receives an incoming call, the comparator block  225  asserts the call presence signal R_ON. The AC/DC input section  220  is consequently activated and makes the transistor T 1  conductive so as to charge the capacitor C to the internal supply voltage (2.5-3V). The voltage at the terminals of the capacitor C supplies the control device  415 . The common block  420  is always active and the control block  230   a  is activated by the call presence signal R_ON so as to cause the buzzer  125  to ring; the conversation presence signal C_ON, on the other hand, is deasserted so that the control block  250   a  is deactivated. 
   As soon as the user lifts the handset  110  in order to answer the call, the fork-shaped hook  115  causes the switch  245  to close and the exchange therefore interrupts the call signal and establishes the connection with the calling telephone. The call presence signal R_ON is therefore deasserted so that the AC/DC input section is deactivated. At the same time, the DC/DC input section  240  makes the transistor T 2  conductive so that the capacitor C which supplies the control device  415  is kept charged. The control block  230   a  is deactivated by the call presence signal R_ON. The conversation presence signal C_ON, on the other hand, is asserted and activates the control block  250   a  (whilst the common block  420  always remains active) so as to permit conversation. 
   The electronic switch  405  is normally open so that the transistor Ts is not conductive. If the voltage between the emitter terminal and the collector terminal of the transistor T 2  falls below a threshold value (for example, of between 0.2 and 0.4V), such as to bring the transistor T 2  towards the non-conductive state, the comparator block  410  closes the electronic switch  405 . The transistor Ts is thus made conductive and shunts towards the reference terminal  215   g  the current which was passing through the transistor T 2  and the capacitor C. This achieves a constant current absorption on the telephone line by the transistors T 2  and Ts, preventing the temporary non-conduction of the transistor T 2  from causing a variation in the current on the telephone line  205  which would be interpreted by the exchange as an acoustic signal. 
   In the telephone described above, when the user lifts the handset  110 , activating the DC/DC input section  240 , the capacitor C is already charged to the internal supply voltage (since it has been charged previously by the AC/DC input section  220  and by the transistor T 1 ). The microphone and the loudspeaker housed in the handset  110  can thus be activated immediately. 
   This solution prevents transient phenomena and consequent electrical interference from arising. This avoids both the use of filters dedicated to reducing electrical interference and the use of speed-up circuits for reducing the duration of the transient phenomenon. The telephone is consequently simpler and more compact. 
   Similar considerations apply if the telephone has a different structure, for example, if it is of the cordless type (with a fixed base connected to the telephone line) or if it includes other units (such as, for example, a hands-free device, a telephone number memory), if different supply voltages or call signals are used, if the buzzer is replaced by another acoustic alarm or another call indicator device such as a light or other visual indicator, if different conversation members are provided (in addition to or instead of the microphone and the loudspeaker housed in the handset), if the supplies and the control device are replaced by other equivalent means, etc. More generally, in the telephone of an embodiment of the present invention, there are first and second supply means which supply, respectively, the control means for the acoustic alarm in a call condition and the control means for the conversation members in a conversation condition; the first supply means further supply the control means of the conversation members in the call condition. 
   In the particular embodiment of the present invention described above, the control block  250   a  (associated with the microphone and the loudspeaker housed in the handset  110 ) is deactivated in the call condition. This reduces the power consumption of the control device  415  in this condition to the minimum, thus making as much power as possible available for controlling the buzzer  125 . 
   Moreover, the fact that the control blocks  230   a ,  250   a  and the common block  420  are formed in a single control device  415  considerably simplifies the structure of the telephone. This also avoids duplication of the circuit elements of the common block  420 , making the control device  415  extremely compact. 
   The particular embodiment of the supply circuits described above is simple and effective. Moreover, the transistors T 1  and T 2  have a lower voltage drop than the diodes used in known telephones; this increases the voltage and hence the power, which is available at the terminals of the capacitor C for controlling the buzzer  125  in the call condition. This embodiment is particularly advantageous for telephone lines which are very long and therefore have a large voltage drop. 
   Similar considerations apply if the control block associated with the buzzer is not deactivated in the conversation condition (for example, in order to be used for the hands-free function), if the control device has a different structure, if the supply circuits are of a different type, for example, with MOSFET transistors, if the electronic switch  405  is replaced by other equivalent means for detecting a state of the transistor T 2  and activating the transistor Ts in dependence on the state detected, etc. 
   The telephone of the present invention may, however, also be formed without deactivation of the control block associated with the microphone and with the loudspeaker housed in the handset in the call condition, with the provision of two separate control units (both connected to the capacitor C) and with the common circuit elements duplicated (with the possibility of deactivating the entire control unit of the conversation members in the call condition), with supply circuits which use diodes (and not transistors), etc. 
   Naturally, in order to satisfy contingent and specific requirements, an expert in the art may apply to the above-described telephone many modifications and variations all of which, however, are included within the scope of protection of the invention, as defined by the following claims.