A WIRE BOUND TELECOMMUNICATIONS DEVICE AND A POWER SUPPLY CIRCUIT

Abstract: Known is a wire bound telecommunications device to be coupled to telecommunication lines comprising a transmission circuit coupled between the telecommunications lines, which transmission circuit comprises a power supply circuit for forming a supply voltage from a telecommunications line voltage, whereby the power supply circuit comprises sensing means for sensing a telecommunications line current and adjustment means for adjusting the supply voltage, a supply voltage terminal being coupled to the sensing means. In the known device, no optimal matching is obtained for the load line of the power supply to a DC-mask for line voltages as a function of a line current as prescribed for a given country. A more optimal matching is proposed. Hereto, the power supply circuit comprises a controllable current source coupled to an adjustment terminal of the adjustment means and that a control input of the controllable current source is coupled to the sensing means, whereby the power supply is arranged such that the adjustment means operates as current sinking or current sourcing means, respectively, so as to cause the supply voltage to increase or decrease, respectively, in accordance with a predetermined function.

Description: "A wire bound telecommunications device and a power supply circuit" The present invention relates to a wire bound telecommunications device to be coupled to telecommunication lines comprising a transmission circuit coupled between the telecommunications lines, which transmission circuit comprises a power supply circuit for forming a supply voltage from a telecommunications line voltage, whereby the power supply circuit comprises sensing means for sensing a telecommunications line current and adjustment means for adjusting the supply voltage, a supply voltage terminal being coupled to the sensing means. Such a wire bound telecommunications device can be a wire bound telephone device, a base station of a cordless telephone apparatus, a facsimile apparatus, a personal computer having a telephone card, or the like. The present invention further relates to a power supply circuit for use in such a telecommunications device. A wire bound telecommunications device of this kind is known from the Philips Application Note "Application of the TEA1093 handsfree circuit", ETT/AN93015 of 29.11.1993, pp. 1-67. On page 39 of this application note, in Fig. 20, a block diagram is given showing a part of a wire bound telephone device, a diode bridge coupled to telephone lines a/b-b/a, and a transmission circuit TEA11 lx coupled between the telephones lines. The transmission circuit TEAlllx, described in more detail in the Philips Datasheet TEA1112, "Low voltage versatile telephone transmission circuits with dialler interface", 16.2.1996, pp. 2-8, and 15, at least partly comprises a power supply circuit for forming a supply voltage from a voltage across the telephone lines. Other components of the power supply circuit are external to the transmission circuit and/or are comprised in a handsfree circuit TEA1093 which is coupled to the transmission circuit and to the telephone lines. The circuit TEA1093 is described in more detail in the Philips Datasheet TEA1093, "Hands-free IC", 9.2.1996, pp. 1-10. The circuitry in the ICs TEA1112 and TEA1093 and the external circuitry can also be embodied and divided over a configuration of ICs and external circuitry in principle having the same overall functionality. The power supply circuit comprises sensing means for sensing a telephone line current in the form of a so-called slope resistor SLPE of e.g. 20 Ohms and internal circuitry in the transmission IC TEA1112. At an output terminal of the power supply circuit a voltage VBB is present for supplying a load, such as a loudspeaker, via a loudspeaker amplifier fed by the voltage VBB. The available line current is determined by the telecommunications network to which the wire bound telecommunications device is to be coupled and the length of the telecommunications line. On the one hand, with fluctuating line currents, the line voltage should not increase above a given DC current mask of a given country and should not increase above a given threshold value determined by a given IC process, but on the other hand maximum power should be available as a function of the line current so that maximum power is available for the loudspeaking function, i.e., maximum loudspeaker should be obtained at a given line current. For adjusting a voltage across the transmission IC such that a maximum line voltage is achieved, adjusting means are provided in the form of an external resistor coupled to an adjustment terminal and internal circuitry in the IC TEA1112. The internal circuitry in the TEA1112 comprises a series arrangement of diodes coupled between the sensing terminal and the adjustment terminal, and an operational amplifier controlling a bipolar transistor. Internally in the IC TEA1112, the adjustment terminal is coupled to an input of the operational amplifier of which an output is controlling the bipolar transistor of which an output terminal forms a supply voltage terminal. If the external resistor is coupled to the supply voltage terminal, the voltage across the transmission circuit decreases with a decreasing value of the external resistor, whereas, if the external resistor is coupled to the sensing terminal, the voltage across the transmission circuit increases with a decreasing value of the external resistor. The internal circuitry of the TEA1112 as described can be found in the block diagram in Fig. 1 on page 3 of said Datasheet of the TEA1112. Adjustment using the external resistor is not optimal to achieve closest following of the DC-mask so as to obtain a maximum output power as a function of the line current. It is thus a disadvantage of the known circuit that no maximum output power as a function of the line current is obtained for powering a load such as a loudspeaker amplifier coupled to a loudspeaker with this maximum power. A general solution to the problem how to achieve optimal matching of the power supply load line to the DC-mask is described in the yet unpublished European patent application No. 96202692.8, filed by the same applicant on 26 September 1996. The general solution proposes a multiple slope power management method. It is an object of the present invention to provide a wire bound telecommunications device of the above kind wherein the DC mask is followed in a more optimal way so as to get more output power for supplying a load. To this end the wire bound telecommunications device according to the present invention is characterized in that the power supply circuit comprises a controllable current source coupled to an adjustment terminal of the adjustment means and that a control input of the controllable current source is coupled to the sensing means, whereby the power supply is arranged such that the adjustment means operates as current sinking or current sourcing means, respectively, so as to cause the supply voltage to increase or decrease, respectively, in accordance with a predetermined function. Herewith, within an operational area of line currents, the voltage between the supply voltage terminal and a sensing terminal, i.e., the voltage across the transmission circuit is in accordance with the predetermined function of the line current. Further embodiments are given in the dependent claims. Claim 3 achieves that the predetermined function is a linear function and claim 4 achieves that the predetermined function is a logarithmic function, so that advantageously different DC-masks of different countries can be tracked. In other, not specifically claimed embodiments, other predetermined functions can easily be obtained by modifying the control element accordingly. A non-linear element can be chosen for the control element having a predetermined transfer characteristic. Claim 5 achieves that a start current is defined so that the circuit can easily be adapted to the demands of various countries. Claim 6 achieves maximum voltage protection. Claim 7 achieves that the voltage between the adjustment terminal and the sensing terminal is constant. This is achieved by said resistor and the described internal circuitry in the TEA1112. According to claim 8 an output voltage is achieved in a way similar to the way disclosed on page 39 of said application note ETT/AN93015. In claim 10 the voltage across the control element is advantageously used to control a further controllable current source, e.g., in the handsfree IC TEA1093. Herewith tracking of the unstabilised supply output voltage and the stabilized supply output voltage is made the same while using simple electronic means. Namely, most of the circuitry is used in common. The present invention will now be described, by way of example, with reference to the accompanying drawings, wherein Fig. 1 schematically shows a block diagram of a wire bound telecommunications device according to the present invention, Fig. 2 shows a circuit diagram of a power supply circuit according to the present invention, Fig. 3 shows a voltage curve to be met, as a function of a line current, according to the present invention, and Fig. 4 shows measurement results of the power supply circuit according to the present invention. Throughout the figures the same reference numerals are used for the same features. Fig. 1 schematically shows a block diagram of a wire bound telecommunications device 1 according to the present invention, such as a wire bound telephone device. The wire bound telecommunications device 1 is coupled to telecommunication lines 2 and 3 and comprises a transmission circuit 4 coupled between the telecommunication lines 2 and 3. The transmission circuit 4, which can be an IC type TEA1112 or TEA 1062 readily available onto the market, comprises a power supply circuit 5 for forming a supply voltage SUP from a telecommunications line voltage V^. The power supply circuit comprises sensing means formed by a so-called slope resistor R SLP _ and internal circuitry in the transmission circuit 4. As described in the following, the power supply circuit 5 further comprises external circuitry and circuitry internal to an handsfree IC 7 of type TEA1093 readily available onto the market. The circuitry according to the present invention is not necessarily divided over said ICs and said external circuitry in the way as described but another functionally equal distribution may occur. In principle, all of the circuitry may be in the form of discrete components but such an embodiment would not be economically feasible. The power supply circuit further comprises adjustment means including a constant voltage resistor for adjusting the supply voltage SUP and a supply voltage terminal LN internally coupled to the sensing means. By coupling the resistor R RE Q to a sensing terminal SLPE, a voltage V^^ PE is increased and by coupling the resistor R^ G to the terminal LN, the voltage V^^ PE is decreased. According to the present invention, the power supply circuit is arranged such that the adjustment means operates as current sinking or current sourcing means, respectively, for increasing or decreasing the voltage V^^ PE and herewith an output voltage VBB of the Integrated Circuit 7, respectively. Further shown in Fig. 1 are a line current 1^., line terminals a/b and b/a, an output buffer capacitor 8, a resistor 9 in series with an interrupter MOSFET 10, a rectifier bridge 11 , a half bridge voltage 1/2 V bridge , an interrupter voltage V^-,^-, a supply current I SU p, a sensing voltage V SU , E , an adjustment resistor R VA for adjusting the handsfree IC in accordance with the adjustment of the IC 4, a ground terminal GND, a reference terminal REG, a line voltage VEE, an adjustment terminal VA, and a reference terminal SREF. The power supply circuit can further comprise a voltage stabilizing circuit. Shown is a transistor 12 included in the voltage stabilizing circuit and a voltage V SUP . VBB . Such a stabilizing is conventional in the art. The output voltage VBB can drive a load. In the given embodiment, the load can be a loudspeaker )not shown) driven by a loudspeaker amplifier (not shown) supplied by the voltage VBB. Fig. 2 shows a circuit diagram of the power supply circuit 5 according to the present invention. The power supply circuit components are distributed over the ICs 4 and 7, and over external components. A controllable current source embodied as a bipolar transistor T3 is coupled to the adjustment terminal REG. A base of the transistor T3 forms a control input 20 of the controllable current source T3, the control input 20 being coupled to the sensing means. By controlling the control input 20 in accordance with a predetermined function of the line current 1^., the adjustment means operates as current sinking or current sourcing means. Shown is a sinking or sourcing current I^ G . Internal circuitry in the IC TEA1112 is as described. Basically two diode drops form an internal voltage source of approximately 1.25 Volts. As a result of this, the voltage at the reference terminal REG is used as a sensing means in said power supply circuit. For current sinking, the resistor R REQ is put between the terminals REG and SLPE, as shown, and for current sourcing the resistor R REG is put between the terminals REG and LN. When applying current sinking, the supply voltage SUP increases with an increasing sinking current. When applying current sourcing, the supply voltage SUP decreases with an increasing sourcing current. Herewith, demands of different countries can be fulfilled. A control resistor R4 is coupled between the base and the emitter of the transistor T3. A bias resistor R5 is coupled in the emitter path of the transistor T3. Herewith, starting of conduction of the transistor T3 is controlled. A current limiting resistor R6 is coupled between the collector of the transistor T3 and the adjustment terminal REG. Herewith, maximum voltage protection is achieved, i.e., the supply voltage SUP is limited to a given upper limit. Optionally, a resistor R10 is coupled between the control input 20 and a resistor R4 having its other end coupled to the sensing terminal SLPE. The power supply circuit 5 further comprises a control element in the form of a bipolar transistor Tl having a resistor Rl in its emitter base path. Herewith, a linear control function is achieved. The resistor Rl can be replaced by a diode (not shown) or by another non-linear control element. Herewith, the control function can be made logarithmic or any other transfer characteristic can be chosen. The collector of the transistor Tl is coupled to a junction 21 via a transistor T2 of which the base is coupled to the collector of the transistor Tl, the collector is coupled to the junction 21, and the emitter is coupled to the terminal LN via a resistor R3. The collector of the transistor Tl is further coupled to the terminal LN via a series arrangement of at least one diode and a resistor R2. Shown are three diodes and a voltage V d across the diodes. The diodes are applied for temperature compensation. Typically, the resistor Rl has a value of 10 kiloOhms and the resistor R s _p_ has a value of 20 Ohms. Herewith, the following voltage relationships hold. The voltage across the resistor R SLPE is 20.1^ Volts. The voltage across the resistor Rl is 20.1^+0.65. The voltage across the resistor R2 is (R2/ 10k). (20.1^+0.65) Volts. The voltage across the resistor R3 is (R2/10k).(20.I li - c +0.65)+V d -0.6 Volts. If the resistors R3 and R4 are equal, the voltage across the resistor R4 is (R2/10k). (20.I Une +0.65)+V d -0.6 Volts. The voltage across the resistor R5 is (R2/10k).(20.I line +0.65)-l-V d -1.2 Volts. The voltage at the adjustment terminal REG is U REG = 1.25+1^.20 Volts. These relationships can easily be verified from the circuit given. Herewith, the voltage across the resistor R4 being the control voltage of the controllable current source T3 is a linear function of the sensed line current 1^.. With the power supply circuit given, the transistor T3 is not conducting when the line current 1^. is below a given threshold value. At higher line currents the output current of the transistor T3 increases linearly with the sensed line current 1^,., and at still higher line currents the transistor T3 is controlled into saturation. In order to control the IC 7 in a similar way, the junction 21 is coupled to a further controllable current source in the form of a bipolar transistor T4 of which the collector is coupled to a current sinking or sourcing terminal VA of the IC 7 via a resistor R8. Shown is a sinking or sourcing current I VA - The emitter of the transistor T4 is coupled to the ground terminal GND via a resistor R7. Fig. 3 shows a voltage curve to be met, as a function of the line current Iu- e , according to the present invention. With the power supply circuit as described, the voltage V LN ^ LPE = N LN . Ωύn for low line currents where the transistor T3 is still non- conductive. At a start current I start the transistor T3 becomes conductive and the voltage V,^. SLPE linearly increases with the line current 1^. At a stop current I atop , when the transistor T3 has become into saturation, the voltage V^^ PE is limited to the value V^.-^. A similar curve holds for the stabilized voltage VBB. Shown are a minimum voltage VBB^ and a maximum voltage VBB,^. The DC-mask (not shown) as prescribed for a given country can thus be tracked as desired. Fig. 4 shows measurement results for V,^^ and VBB of the power supply circuit 5 according to the present invention. As can be seen, the measured curves are close to the theoretical curves as given in Fig. 3. In view of the foregoing it will be evident to a person skilled in the art that various modifications may be made within the spirit and the scope of the present invention as hereinafter defined by the appended claims and the present invention is thus not limited to the examples provided.

Claims: CLAIMS: 1. A wire bound telecommunications device to be coupled to telecommunication lines comprising a transmission circuit coupled between the telecommunications lines, which transmission circuit comprises a power supply circuit for forming a supply voltage from a telecommunications line voltage, whereby the power supply circuit comprises sensing means for sensing a telecommunications line current and adjustment means for adjusting the supply voltage, a supply voltage terminal being coupled to the sensing means, characterised in that the power supply circuit comprises a controllable current source coupled to an adjustment terminal of the adjustment means and that a control input of the controllable current source is coupled to the sensing means, whereby the power supply is arranged such that the adjustment means operates as current sinking or current sourcing means, respectively, so as to cause the supply voltage to increase or decrease, respectively, in accordance with a predetermined function. 2. A wire bound telecommunications device according to claim 1, wherein the power supply circuit comprises a control element for generating a control voltage in accordance to a predetermined function. 3. A wire bound telecommunications device according to claim 2, wherein the control element comprises a bipolar transistor having a resistor in its emitter base path such that a linear function is obtained. 4. A wire bound telecommunications device according to claim 2, wherein the control element comprises a diode in the emitter base path such that a logarithmic function is obtained. 5. A wire bound telecommunications device according to claim 1, wherein the controllable current source is a bipolar transistor and a control resistor is coupled between the control input and a first main electrode of the bipolar transistor, and wherein the bipolar transistor starts conducting if a voltage across the control resistor representative of the control voltage exceeds a given threshold value. 6. A wire bound telecommunications device according to claim 1, wherein a current limiting resistor is coupled between an output of the controllable current source and the adjustment terminal. 7. A wire bound telecommunications device according to claim 1, wherein a constant voltage resistor is coupled between the adjustment terminal and an output terminal of the sensing means. 8. A wire bound telecommunications device according to claim 1, wherein the supply voltage is fed to a voltage stabilizing circuit of which an output forms the supply for a load. 9. A wire bound telecommunications device according to claim 8, wherein the load is a loudspeaker coupled to the supply via an amplifier fed by the supply. 10. A wire bound telecommunications device according to claim 8, wherein the voltage across the control element is fed to a further controllable current source for controlling current sinking or sourcing of a reference terminal of the voltage stabilizing circuit. 11. A power supply circuit for use in a wire bound telecommunications device to be coupled to telecommunication lines, which telecommunications device comprises a transmission circuit coupled between the telecommunications lines, and the power supply circuit for forming a supply voltage from a telecommunications line voltage, whereby the power supply circuit comprises sensing means for sensing a telecommunications line current and adjustment means for adjusting the supply voltage, a supply voltage terminal being coupled to the sensing means, characterised in that the power supply circuit comprises a controllable current source coupled to an adjustment terminal of the adjustment means and that a control input of the controllable current source is coupled to the sensing means, whereby the power supply is arranged such that the adjustment means operates as current sinking or current sourcing means, respectively, so as to cause the supply voltage to increase of decrease, respectively, in accordance with a predetermined function.

Inventors: SOREE JOHANNES J, VAN LEEUWEN LAURENS CORNELIS, SOREE, JOHANNES, J., VAN LEEUWEN, LAURENS, CORNELIS
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1998
Main classification: H04B3
IPC codes: H04B3, H04M1, H04M9, H04M19