GB1568329A - Circuit arrangement for loudspeaking telephone set - Google Patents
Circuit arrangement for loudspeaking telephone set Download PDFInfo
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- GB1568329A GB1568329A GB6251/78A GB625178A GB1568329A GB 1568329 A GB1568329 A GB 1568329A GB 6251/78 A GB6251/78 A GB 6251/78A GB 625178 A GB625178 A GB 625178A GB 1568329 A GB1568329 A GB 1568329A
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- channel
- circuit arrangement
- loudspeaker
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- 239000000463 material Substances 0.000 claims description 2
- LJIDRFNRDLYHNC-UHFFFAOYSA-N oleracein E Natural products C1CN2C(=O)CCC2C2=C1C=C(O)C(O)=C2 LJIDRFNRDLYHNC-UHFFFAOYSA-N 0.000 claims description 2
- 239000004065 semiconductor Substances 0.000 claims description 2
- 238000011144 upstream manufacturing Methods 0.000 abstract 1
- 230000009467 reduction Effects 0.000 description 21
- 230000002238 attenuated effect Effects 0.000 description 7
- 230000002829 reductive effect Effects 0.000 description 7
- 230000005540 biological transmission Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 230000006978 adaptation Effects 0.000 description 4
- 230000000875 corresponding effect Effects 0.000 description 4
- 238000010276 construction Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000010079 rubber tapping Methods 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
- H04M9/10—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic with switching of direction of transmission by voice frequency
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Interconnected Communication Systems, Intercoms, And Interphones (AREA)
Abstract
This circuit arrangement has first and second attenuators (T0, T1) in the transmitting channel and in the receiving channel downstream of the pre-amplifiers (V1) or upstream of the power amplifier stages (V3). Thanks to additional attenuation-reducing components (R'3, R5), the channels never appear to be dead and dialogue is facilitated. With a self-regulating circuit (R6, R7, T'2), amplitude is limited at the output of the power amplifier stage (V3) with the result that impermissible or function-impairing amplitude values are avoided. <IMAGE>
Description
(54) A CIRCUIT ARRANGEMENT FOR A LOUDSPEAKING TEI,EPHONE SET (71) We, DASY INTER S.A., of 19, Rue du Rhone, Geneva, Switzerland, a body corporate organized according to the laws of Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to an improvement in or further development of the invention described in our application no.
35322/77 (Serial No. 1,550,721). This application claims a circuit arrangement for a loudspeaking telephone set with a twin-core connection line and a two-way signal transmission system comprising a transmitting channel driven by the microphone of the loudspeaking telephone set and a receiving channel driving the loudspeaker of the loudspeaking telephone set, and the channels respectively have pre-amplifier stages and final amplifier stages and the pre-amplifier stages are preceded by a first attenuating member, the final amplifier stages are preceded by a second attenuating member, the attenuating members are driven by control voltages derived from the speech current of each channel, and with an attenuation reducing member operating on the second attenuating member of the transmitting channel.
In the case of such a loudspeaking telephone set in the quiescent condition the attenuation of the channel through the respective first attenuating member in the direction of transmission is low or overridden and the attenuation of the channel through the second attenuating member is however large. The control voltage derived from the pre-amplified speech current in one channel, and which is applied to the first attenuating member of the other channel for overriding the attenuation, is applied additoinally to the second attenuating member of the one channel itself for decreasing or overriding the attenuation of this channel. The attenuating members are so driven with a staggered timing via the first and second delay members in the control circuit of each channel that reliable functioning is ensured.The same control voltage, obtained from the output of the preamplifier, is however also used for amplitude limitation and for this purpose it is passed via a self-regulating circuit to the first attenuating member connected with the input of the pre-amplifier. The first attenuating member is so controlled by the self-regulating circuit that when the amplitude increases in the output signal of the pre-amplifier the attenuation of the input of the pre-amplifier is overridden. Accordingly an effective limitation of the amplitude of the output signal of the preamplifier is ensured.
However it is also necessary to bear in mind that further amplifier stages are arranged following the pre-amplifier stages.
This applies especially for the end stage following the second attenuating member.
This latter end stages accordingly not included in the automatic amplitude limitation.
Owing to tolerances in the characteristics of the components used in the end stage and, respectively, its supplying circuit elements very large amplitude values may occur in the output signal of the end stage despite the amplitude limiting self-regulation with respect to the input amplifier or respectively of the pre-amplifier stages.
These large amplitudes are dangerous for two reasons: In the transmitting channel such amplitudes lead to corresponding amplitudes in the twin-core subscriber connection line owing to transmission through the output transformers. In this line however only certain maximum amplitudes are permitted in accordance with the regulations of the loudspeaking telephone set.
Furthermore the very large amplitudes occurring in the transmitting channel can lead to corresponding amplitudes in the receiving channel owing to transmission from the subscriber connection line via the input transformer and this may give rise to difficulties as regards satisfactory operation of the complicated loudspeaking telephone set control.
One aim of the invention is that of so developing the circuit arrangement in accordance with the main patent that despite simple regulation in the case of channel attenuation an individual adaptation of the attenuation to the requirements is made possible. In this respect more especially the line should not under any circumstances appear to the caller to be dead and the efficiency of the amplitude limiting selfregulating circuit is to be increased.
At least in the transmitting channel the first and the second attenuating members have attenuation reducing members, which are constantly effective and bring about adjustable or selectable reduction in attenuation even if the attenuating members themselves are switched over between minimum attenuation (attenuation of 0 ,Ó) and maximum attenuation (attenuation of 100%).
If owing to an incoming signal coming from the subscriber connection cable or line the receiving channel is open and if by means of the control circuit connected with the receiving channel the transmitting channel is attenuated, the latter will not be completely switched off by the first attenuating member. The reduction in attenuation by the attenuation reducing members associated with the first and the second attenuating members of the transmitting channel, can be so selected that owing to the summated attenuation of the two attenuation reducing members in fact only such a maximum attenuation of the transmitting channel is allowed that local noise from the space around the loudspeaking telephone set is allowed to pass without the receiving channel which is functioning being attenuated.
The limit for local noise to be allowed to pass in the subscriber connection line can for examp'e be set at 50 dB. The caller then has the impression that the line is always open, although the person at the other end of the line is not using a conventional handset telephone but a loudspeaking telephone set. For the person called there is no disadvantage in this respect, because the attenuation production is so set on the one hand with respect to the attenuation of the respective other channel on the other hand that on the basis of the local noise at the called end the signals passing from the caller to the receiving channel can additionally be attenuated in a manner, which would cause an excessive reduction in volume.The called subscriber or, strictly speaking, the user of the loudspeaking telephone set has in the case of such a form of the transmission channel the further advantage that he can more readily draw attention to himself by interruption because the signal passed via the microphone into the transmission channel is not completely attenuated and instead will pass with a certain, albeit reduced amplitude to the subscriber connection.
Naturally it is also possible for the receiving channel to be equipped effectively in this manner with an individually reduced attenuation in order to facilitate interruption in the opposite direction as well.
Finally it is also possible, in the case of equipment with attenuation reduction in both channels, to prefer one channel as compared with the other one. In the case of a manager 5 telephone for example the attenuation reduction in the transmitting channel will be selected to be more pronounced than in the receiving channel.
This is made readily possible by the adjustable or selectable attenuation reduction.
As a result the manager can easily interrupt the person at the other end of the line at any time so that he can no longer be heard while on the other hand as long as the manager is speaking, interruption is hardly possible. This system is also capable of op erating if only the manager has a loudspeaking telephone set and the person at the other end of the line has a conventional handset telephone. It is also readily possible to limit the preferential status of the mana get 5 telephone to cases in which this telephone is used for conversing with telephones on the same premises and to bring about mutual adaptation of the attenuation reduction in the transmitting channel and in the receiving channel of the manager's telephone as soon as telephone conversations are to be carried out with subscribers outside the premises.If a manager's telephone is to be given a preferential status in all cases with respect to other loudspeaking telephone sets, it is appropriate not only to make attenuation reduction in the transmission channel more pronounced than in the receiving channel in the case of the mana get 5 telephone but also, as the exact opposite, to make the attenuation reduction in the receiving channel more pronounced than in the transmitting channel in the loudspeaking telephone sets of the other equipments. In these circumstances it is not necessary to take into account as regards the manager's telephone whether it is a question of telephone conversations with persons within the same building or premises or of telephone conversations with external telephone subscribers: The attenuation reduction in the transmitting channel of the manager's telephone is only slightly more pronounced than in the receiving channel but nevertheless the mana get 5 telephone can in all cases override the loudspeaking telephone sets provided for employees in the premises, because in the case of the latter telephones the attenua tion reduction in the receiving channel is more pronounced and as a result any interruption on the part of the manager, owing to the more pronounced attenuation reduction in the receiving channel in the case of these telephones, will result in the complete attenuation of the transmitting channel.
The attenuation members will consist generally of transistors, whose emitter collector path is connected between the respective amplifier input and ground or respectively the minus pole of the current supply.
It is particularly convenient to use MOS
FET transistors, in the case of which the current path controlled by the control electrode then plays the same role. In the case of such a construction of the attenuation members it is particularly simple to bring about attenuation reduction. For this purpose it is sufficient to connect a resistor in series with the current path through the transistor. In this respect it can be a question of a resistor with an adjustable resistance value.
The simplest circuit arrangement can be ensured if the board with the printed circuit and the circuit elements for the loudspeaking telephone set is provided with an open bridge between the amplifier input and the respective attenuating member. If this bridge is then closed by a conducting connection attenuation reduction is then dispensed with. In accordance with the desired specific degree of reduction of attenuation it is then possible to replace the conducting connection by a resistor. In the case of the resistor it can be a question of a fixed resistor or an adjustable resistor.
Finally in particular cases it is also possible to construct the brdige as a series circuit arrangement made up of a two-way switch arranged to cooperate with a parallel circuit arrangement made up of two resistors with different resistances. If the two-way switch is operated in a manner dependent on other functions of the equipment as for example in accordance with a number of digits of the number dialled, for example in the case of conversations within the same building (in which case the dialled number will have four digits at the most) the two-way switch can be so actuated that the resistor with the higher resistance is used as the attenuation reducing member while in the case of dialling numbers with a larger number of digits a resistor is used as an attenuation reducing member, which has a smaller resistance and therefore leads to a lesser reduction in attenuation.
Furthermore in this case for amplitude limitation in each channel the output signal of the channel is used. The efficacy of amplitude limitation is therefore substantiallv enhanced and in particular involves all stages of the channel It is therefore no longer possible for tolerances in the data of the individual components of the stages used to lead to amplitude values, which would not be in accordance with regulations or would even impair proper functioning.
Cross-talk between subscriber lines is also prevented and furthermore there is no possibility of blocking of the loudspeaking telephone set owing to spurious signal transmission. Owing to the type of the selected self-regulating amplitude limiting circuit and its ready adaptation it is possible to keep the output amplitude between one piece of equipment and the next within close limits. In accordance with the specific complexity of the adjusting means adopted fluctuations in the maximum output amplitude of the transmitting channel of at the most 4% can easily be ensured. The breadth of fluctuation can be reduced to below 1% of the desired value if the complexity of the setting or adjusting means is somewhat greater.
The amplitude limiting self-regulating circuit operates particularly efficaciously and expediently if a transistor is used as an attenuating member. Owing to the powerless possibility of control a field effect transistor, more particularly an MOS-FET transistor is particularly suitable for this purpose. Such transistors are also expediently used in the self-regulating circuit, and the latter can also consist of one transistor, to whose control electrode the output signal of the end stage is applied.
In the receiving channel it is possible to provide instead of the loudspeaker of the loudspeaking telephone set an additional loudspeaker which can be put in circuit.
The amplitude limiting self-regulating circuit then remains effective irrespectively of which of the two loudspeakers is functioning. In the case of an additional loudspeaker, which will be a loudspeaker arranged outside the enclosure of the loudspeaking telephone set, in the case of a volume which is regulated by the selfregulating circuit simultaneously, the danger of malfunctiomng due to sidetone acting on the loudspeaking telephone set microphone owing to sound transmitted through solids is still further reduced.
In the drawings, which comprise all features not described in detail in what follows, the invention is shown by way of example.
Figure 1 shows a receiving channel of a loudspeaking telephone set.
Figure 2 shows the transmitting channel of the same loudspeaking telephone set.
In the figures some parts are represented diagrammaticaly for purposes of simplification. Furthermore some features have been omitted, which will be self-evident to those skilled in the art. Finally it is to be pointed out that the connection points of the two figures are denoted by like reference letters.
Figure 1 shows on the top left the microphone Mi of the loudspeaking telephone set.
At the bottom left in figure 2 the loudspeaker L of the loudspeaking telephone set, and an additional or ancillary loudspeaker L' are indicated, the latter being put into operation via a two-way switch S in lieu of the loudspeaker L. At the bottom left in figure 2 the subscriber connection line a, b is indicated.
The transmitting channel indicated at the top in figure 1 consists of a microphone Mi converting sound into an electric signal.
The signal is amplified by an amplifier V1 serving as a pre-amplifier and is passed on to a further amplifier V2, also belonging to the amplifying stages, to the amplifier V3 serving as the end stage of the transmitting channel. The output signal of this amplifier is passed via the transformer Trl, serving as the output transformer of the transmitting channel, and lines a', b' and also the transformer Tr2, serving as the input transformer of the receiving channel, to the subscriber connection line a, b. The receiving channel is shown at the bottom in figure 2:
Incoming signals transmitted by the subscriber connection line a, b are passed via the transformer Tr2, serving as the input transformer, to the amplifier V4 serving as the input amplifier and from the latter to the amplifier V5 serving as the end stage of the receiving channel.The output signal of the amplifier V5 is applied, in accordance with the specific setting of the twoway switch S, to the loudspeaker L or the ancillary loudspeaker L'.
In the input circuit of the amplifier V2 there is provided a transistor To, serving as the first attenuating member and its emitter collector path extends between the input and the negative terminal of the power supply. By the same token in the transmitting channel a transistor Tl is connected as a second attenuating member with the input of the amplifier V3. In the receiving channel the transistors TO and respectively T1 are represented by the transistor T13 connected with the input of the amplifier V4 and the transistor T14 connected with the input of the amplifier V5.
Respectively between the amplifiers V2 and V3 and respectively V4 and V5 of the tranmitting and respectively receiving channel a control voltage is tapped which is derived from the speech current. This control voltage is passed to a control circuit which is shown centrally towards the bottom of figure 1 and on the right hand side of this figure while in figure 2 it is shown centrally towards the top and to the right hand side. These control circuits respectively control via a first delay member C8,
Rl 1 and respectively C13, R19 the first attenuating member of the other channel and via a second delay member C9, R13 and respectively C14, R20, connected with the output of the first delay member, they control the second attenuating member of the channel itself.As a result there is a time lagged driving of the transistors TO,
Tl and respectively T13, T14 serving as attenuating members.
Furthermore at the output of the end stage of each channel a signal is tapped for amplitude limitation and passed on via a self-regulating circuit indicated in figure 1 at the bottom and to the left of the centre part and in figure 2 at the top and to the left of the centre part.
In this respect it is important that in the transmitting channel there is not only a connection in series of a resistor R5 with the transistor Tl serving as the second attenuating member but also the connection of a resistor R'3 is connected with the transistor TO serving as the first attenuating member, this resistor R'3 being connected in the same manner as the resistor R 5.
Without the use of the resistor R'3 in previous practice the transmitting channel was completely attenuated by the transistor TO when the receiving chanel is switched into the conducting state. This was brought about by the feature of using a suitable driving current from the control circuit of the receiving channel, the current being passed via the line d to completely switch on. the transistor TO Its resistance therefore assumes a negligibly small value.
As a result the potential of the input of the amplifier V2 was reduced to the potential of the negative terminal of the power supply or respectively earth. Signals incoming from the microphone Mi could no longer be amplified. As a result the resistor R5 was also substantially ineffective.
The transmitting channel appeared to be dead.
The effect of the resistor R'3 connected in series with the emitter collector path of the transsitor TO resides more specifically in that the input of the amplifier V2 is not completely attenuated. This leads to various different effects.
An output signal of the amplifier V2 and therefore of the amplifier V3 as well still exists. This output signal will pass via the transformer Trl to the connection line a, b as well. This line therefore appears to be dead.
Furthermore the output signal of the amplifier V2 passes via the capacitor C7 to the control circuit of the transmitting channel as well. In this respect the resistance of the resistor R'3 is so selected that signals pro duced at the microphone Mi up to a certain limit of for example 50 dB will not lead to the production of a control signal owing to the control circuit of the transmitting channel. Therefore no signal will be passed to the line c. The transistor T13 representing the first attenuating member in the receiving channel is accordingly switched off. If however the threshold value is exceeded, the control circuit of the transmitting channel will produce a control signal, which is passed to the control line c, despite the fact that at the loudspeaking telephone set the receiving channel is at the present switched on.As a result attenuation of the receiving channel will occur via the transistor T13. In accordance with the specific size of the signal appearing at the output of the amplifier V2 this may progress to such a degree that finally via the control line d from the control circuit of the receiving channel the transistor TO completely overrides the attenuation of the transmitting channel. By raising one's voice it is accordingly possible to interrupt.
Finally the signal passed by the switched on receiving channel to the loudspeaker L is radiated by the latter. The radiated sound will also pass to the microphone Mi at the input of the transmitting channel.
Since however owing to the resistor R'3 no total attenuation of the input amplifier V2 is brought about by the transistor TO, the sound radiated by the loudspeaker L, which is converted by the microphone Mi back
into an electrical signal, will cause response of the control circuit of the transmitting channel. If the sound volume radiated by the loudspeaker L is so large, on exceeding a threshold value the control circuit - of the
transmitting channel will again receive a control signal and via the control line c it will be connected with a transistor T13, which accordingly attenuates the input of the receiving channel. Accordingly automatic volume control of the loudspeaking telephone set will be provided for. Owing to this feature the sound volume will be constantly and automatically regulated to below a maximum value.The fact that via the microphone Mi of the loudspeaking telephone set an excessively loud radiation of sound from the loudspeaker L of the loudspeaking telephone set is automatically attenuated also improves the overall functioning of the loudspeaking telephone set.
Acoustic feedback between the loudspeaker
L and the microphone Mi is thus effectively suppressed so that it is possible to select advantageously short switching times without any danger and the reduced attenuation as described can be employed.
The loudspeaker L of the loudspeaking telephone set is integrated in a conventional manner with the microphone Mi in one and the same enclosure. Owing to this feature the microphone Mi is in no way only influenced through the surrounding air by the loudspeaker L and instead sound can also be transmitted in the enclosure or housing from the loudspeaker L to the microphone Mi. Owing to the use of the ancillary loudspeaker L' it is possible to ensure the advantage that if the ancillary loudspeaker L' is not incorporated in the enclosure of the loudspeaking telephone set, and instead is used as an additional loudspeaker without the enclosure, the sound transit time to the microphone Mi will be increased.The effects of radiated sound will be reduced so that the ancillary loudspeaker L' can be used to produce a greater volume than would be the case with a loudspeaker L integrated in the enclosure.
Owing to self-regulation of volume via the microphone Mi this matter is automatically taken into account: In the case of the use of the ancillary loudspeaker L' reverse attenuation of the open receiving channel will only occur at a substantially higher volume.
Since in the transmitting channel there is not only a series connection of the resistor
R'3 with the transistor TO but also a series connection of the resistor R5 with respect to the transistor T1 and the control voltage for the control circuit is tapped at the input of the latter-mentioned attenuating member, by a suitable choice of the resistances it is possible to achieve good matching of the attenuation in a simple manner.
The reduction in attenuation by the resistor R'3 is so selected that it complies with the requirements of interrupting and of automatic volume regulation or control.
For the output signal, passed to the lines a' and b', of the transmitting channel the attenuating effects of the transistors TO and T1 summate and accordingly there is also a summation of the attenuation reduction by the resistor R'3 and respectively R5 connected in series with transistors TO and Ti.
The resistance of the resistor R5 can therefore be so selected that, in accordance with the resistance, selected in accordance with other requirements, of the resistor R'3 it is possible to ensure that the line a', b' does not appear dead, when the receiving channel is switched on.
In the above explanations the basic assumption was made that the transmitting channel is equipped with a corresponding attenuation reducing system. It is naturally possible also to equip the receiving channel additionally with a similar attenuation reducing system. This can be produced by resistor R'5, coresponding to the resistor
R5 in transmitting channel and respectively the resistor R'23 corresponding to the resistor R'3 in the transmitting channel.
The function of this attenuation reduction is. in all -respects- comparable with the effect of the attenuation reduction in the transmitting channel-: For the. user of the loudspeaking telephone set the -receiving channel does not appear dead even when he himself is speaking (that is to say when the transmitting channel is switched on).
There is still a certain degree of residual acoustic feedback via the loudspeaker L or respectively the ancillary loudspeaker L.
Furthermore interruption is facilitated, because a signal can pass to the control line d even when a signal, attenuating the receiving channel, is simultaneously present in the control line c.
As regards selecting the values of the resistors R'3, R5, R'5, R'23 the following is to be taken into account:
Since to a certain degree both channels are constantly open or switched on great attention should be paid to the type of interrupt control signals, which are produced in the control circuits. The resistors
R'3 and R'23 could therefore never have a resistance higher than the threshold value, at which the transistors T2 and T3 in the control circuit of the transmitting channel and the transistors T8 and T9 in the- control circuit of the receiving channel are saturated. The same applies as regards automatic volume control or regulation for the resistors R5 and R'5 respectively.
On choosing the resistances of these- re- sistors it is furthermore important fat the resistances to be positively correlated with the 'acoustic conditions of the enclosure.
If these conditions are excellent vowing to it being -possible to ensure good acoustic separation of the loudspeaker L from the microphone Mi, it is possible to use relatively open channels, that is to say relatively high attenuation reductions produced by the use of relatively high resistances.
The equipment will then function In the pseudoduplex or respectively pseudomultiplex mode. The subscribers will have the impression that the - two liners br, In the case of conference circuits, all lines are open the whole time.
If the resistors R'3, R5, R'5 and R'23 are used, there are furthermore good possibilities for providing fo individual adapta- tion of the circuit arrangement of the loud-- speaking telephone set to the acoustic conditions of the respectively used enclosure The construction of the a.tfenuation reducing member as a resistor connected between the amplifier input and one of "the transistors TO, TI, T13 and respectively
T14 has alreadybeen described. instead of this resistor it is also possible to use a potentiometer or respectively an adiustable resistor with the same effect, which is-con- nected-between the control lines,' mor nar- ticularly the control'lines c, d and earth.
The - intermediate' tapping point is connec- ted--- with the eontroI electrode of the transistor. It- is furthermore possible- to use other voltage dividers connected- between the.control line and the respective transistor
TO, T1, Ti 3,- T14.
- The control voltage for the amplitude limiting automatic control or automatic regulation circuit is then tapped only after the end stage, that is to say following the amplifier V3 and, if the receiving channel is also to be provided with such an automatic control circuit, following the amplifier
VS.
In the transmitting channel a transformer
Trl, serving as the output transformer, is connected with the output of the amplifier
V3 via a capacitor C5. Between the latter and the transformer Trl the voltage is tapped and passed via a capacitor C6 to the control electrode of a transistor T'2. This can be carried out directly. In figure 1 however an embodiment is shown in the case of which the output signal of the end stage of the transmitting channel is passed via a capacitor C6 to an intermediate tap ping point of a voltage - divider made up of resistors R6 and R7. This voltage divider is for its part connected between the control electrode of the transistor T'2 and the plus pole - of the power supply.
The emitter collector path of the transistor T'2 can be connected between the positive terminal 'of the power supply and earth or respectively the negative terminal of the power supply. In this case a -capacitor C'6 is connected between the collector and hearth and this capacitor introduces a certain time constant into the control system.The collector is furtherm-ore connected via a diode
D1 Mth the -control-- electrode of -the tran sistor - T0, which represents the first at tenuating member connected- with the input of the amplifier V2. - The control electrode of the transistor TO is furthermore connec- ted via the diode D2 with the control line of the control-circuit of the receiving channel.The diodes are connected in the mantier indicated in figure 1 so that the control voltages of the control circuit on the one hand - and - of the amplitude - limiting self- regulating circuit on the other cannot pass to the respective other circuit though how- ever the two control voltages are superimposed on each other and applied to the control electrode bf the - transistor. The latter therefore acts as an attenuating mem bef for the prope'r 'f\1nctioning of the loudspeaking telephone set with the i,ossibility Of interruption. Its attenuating function is furthermore àlso- used to bring about am plitude limitation- of the signal-passed to the output transformer of the trans-m-itting channel (transformèr Trl), and for this purpose this signal' itself""is' set back via the 'self regulating circuit to the input of the channel. or respectively the attenuating Member provided at-this input
In the receiving channel the amplitude limiting self-regulation occurs in a.- -c-orres- ponding manner.In the 'sell-regulation-' dr- cuit shown in this figure the capaoitor 10 corresponds. to the capacitor C6, the vel- tage divider made up of the resistom ll14 and R15 corresponds to the voltage divider made of the resistrs-'R6-and-67,the -tr8nr sistor T7 corresponds to -the transistor T'2, the capacitor CZ10 corresponds to the -capa- citor Cr6 and the diode D3, 1)4 correspond to -the- diodes D1- and-D2. In this case as well the output signal of the end stage is tapped at the end stage of the amplifier V5 and provides for a feedback action on the transistor T13 via the self-regulating circuit. The transistor T13 as the first attenuating member, of the receiving channel is connected with the input of the amplifier
V4.
Owing ot the possibility of powerless con
trol it is preferred to use field effect tran
sistors both as the attenuating members in the two channels and also as the transistors
used in the self-segulating circuit. In this respect it is particularly preferred to use
MOS-FET's. If furthermore the various
transistors in the control circuits are in the form of field effect transistors, it is parti
cularly preferred to use integrated semicon
ductor components, which are constructed in CMOS technology, that is to say they
respectively comprise combinations of two
MOS-FET's.
In the receiving channel besides the loudspeaker L integrated in the loudspeaking
telephoning set enclosure, an ancillary loud
speaker L' is provided, which via a two-way swicth can be put into operation instead of
the loudspeaker integrated in the loud
speaking telephone set enclosure. This can
have advantages for the self-regulating circuit, since there will be no acoustic coupling through the material of which the enclosure is made with the microphone Mi integrated in the loudspeaking telephone set.
WHAT WE CLAIM IS: - 1. A circuit arrangement for a loudspeaking telephone set with a twin-core connection line and a two-way signal transmission system comprising a transmitting channel driven by the microphone of the loudspeaking tele one set and a receiving channel driving th loudspeaker of the loudspeaking telephone set, each channel having a preamplifier stage and a final amplifierstage, each preamplifier stage being preceded by a respective first attenuating member, each final amplifier stage being preceded by a respective second attenuating member, - the attenuating me-mbers- being driven according -to control voltages being proportional - to the speech current of each channel, and with an attenuation reducing member - operating on the second attenua ting member of the transmitting channel,
characterised in that a further attenuation
reducing member is - provided for -the first
attenuating member - of at least the transmitting channel.
2. A circuit arrangement in accordance with'- claim 1, wherein the attenuating rnemz bers are transistors, whose emitter collector
paths are connected between the respective
amplifier input and earth and- the negative
terminal- respctively of the power supply.
3. A circuit arrangement in accordance
with claim - 1, wherein the attenuation re
ducing members have an ohmic resistance
connected in series with the attenuating
members.
4. A circuit arrangement in accordance
with claim 3, wherein the resistance- can be adjusted.
5. A circuit arrangement in accord
ance with claim 3, wherein the attenuation reducing member its an electrical resistor
which can be selectively connected between
the transistor and the amplifier input.
6. A circuit arrangement in accordance
with claim 3, wherein the attenuation re
ducing member is a potentiometer, whose
one end terminal is connected with the con
trol line, whose other end terminal is con
nected with earth or the negative terminal
of the power supply and whose intermediate
tap is connected with the control electrode
of the transistors
7. A circuit arrangement in accordance
wtih claim 1, wherein in the receiving channel a two-way switch is connected at the
input of the loudspeaker of the loudspeak
ing telephone set and by means of the two
way switch instead of the loudspeaker an
ancillary loudspeaker can be connected, said
ancillary loudspeaker being provided out
side the loudspeaking telephone set enclo
sure.
8. A circuit arrangement in accordance
with claim 1, wherein there is provided at least in the transmitting channel a self
regulating amplitude limiting circuit and wherein the output voltage of the final am
plifier stage of the channel itself is applied to said self-regulating amplitude limiting
circuit as a control voltage therefor.
9. A circuit arrangement in accordance with claim 8, wherein the control voltage
is tapped between a capacitor connected with the output of the final amplifier stage
of the transmitting channel and the output transformer of the transmitting channel.
10. A circuit arrangement in accordance with claim 8, wherein the first attenuating member, driven by the control voltage, is a
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (15)
1. A circuit arrangement for a loudspeaking telephone set with a twin-core connection line and a two-way signal transmission system comprising a transmitting channel driven by the microphone of the loudspeaking tele one set and a receiving channel driving th loudspeaker of the loudspeaking telephone set, each channel having a preamplifier stage and a final amplifierstage, each preamplifier stage being preceded by a respective first attenuating member, each final amplifier stage being preceded by a respective second attenuating member, - the attenuating me-mbers- being driven according -to control voltages being proportional - to the speech current of each channel, and with an attenuation reducing member - operating on the second attenua ting member of the transmitting channel,
characterised in that a further attenuation
reducing member is - provided for -the first
attenuating member - of at least the transmitting channel.
2. A circuit arrangement in accordance with'- claim 1, wherein the attenuating rnemz bers are transistors, whose emitter collector
paths are connected between the respective
amplifier input and earth and- the negative
terminal- respctively of the power supply.
3. A circuit arrangement in accordance
with claim - 1, wherein the attenuation re
ducing members have an ohmic resistance
connected in series with the attenuating
members.
4. A circuit arrangement in accordance
with claim 3, wherein the resistance- can be adjusted.
5. A circuit arrangement in accord
ance with claim 3, wherein the attenuation reducing member its an electrical resistor
which can be selectively connected between
the transistor and the amplifier input.
6. A circuit arrangement in accordance
with claim 3, wherein the attenuation re
ducing member is a potentiometer, whose
one end terminal is connected with the con
trol line, whose other end terminal is con
nected with earth or the negative terminal
of the power supply and whose intermediate
tap is connected with the control electrode
of the transistors
7. A circuit arrangement in accordance
wtih claim 1, wherein in the receiving channel a two-way switch is connected at the
input of the loudspeaker of the loudspeak
ing telephone set and by means of the two
way switch instead of the loudspeaker an
ancillary loudspeaker can be connected, said
ancillary loudspeaker being provided out
side the loudspeaking telephone set enclo
sure.
8. A circuit arrangement in accordance
with claim 1, wherein there is provided at least in the transmitting channel a self
regulating amplitude limiting circuit and wherein the output voltage of the final am
plifier stage of the channel itself is applied to said self-regulating amplitude limiting
circuit as a control voltage therefor.
9. A circuit arrangement in accordance with claim 8, wherein the control voltage
is tapped between a capacitor connected with the output of the final amplifier stage
of the transmitting channel and the output transformer of the transmitting channel.
10. A circuit arrangement in accordance with claim 8, wherein the first attenuating member, driven by the control voltage, is a
transistor, whose emitter collector path is connected between the input of the respective pre-amplifier and earth and respectively the negative terminal of the power supply and the output signal of the self-regulating circuit is connected with the control electrode of the transistor.
11. A circuit arrangement in accordance with claim 10, wherein there is applied to the control electrode of the transistor not only the output signal of the self-regulating circuit but also a control signal derived from the speech current on the respective other channel and the application of the two signals is via a respective diode, whose polarity direction switches on the connection between the control electrode of the transistor for the control signals and however separates the control circuits from each other.
12. A circuit arrangement in accordance with claim 10, wherein the self-regulating circuit also consists of a transistor to whose control electrode the output signal of the end stage of the same channel is applied via a capacitor.
13. A circuit arrangement in accordance with claim 12, wherein a voltage divider is connected with the control electrode of the transistor and the voltage divider has an intermediate tap, to which the output signal of the final amplifier stage is applied.
14. A circuit arrangement in accordance with claim 8, wherein in the receiving channel between the tap for the control voltage of the final amplifier stage for the self-regulating amplitude limiting circuit and the loudspeaker a two-way switch is provided, said two-way switch enabling an ancillary loudspeaker to be connected, instead of the loudspeaker, said ancillary loudspeaker being provided outside the loudspeaking telephorie set enclosure.
15. A circuit arrangement for a loudspeaking telephone set substantially as herein described with reference to and as illustrated in the accompanying drawings.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19772751248 DE2751248C3 (en) | 1977-11-16 | 1977-11-16 | Circuit arrangement for a hands-free telephone |
| DE19772751261 DE2751261C3 (en) | 1977-11-16 | 1977-11-16 | Circuit arrangement for a hands-free telephone with automatic signal amplitude limitation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1568329A true GB1568329A (en) | 1980-05-29 |
Family
ID=25773095
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB6251/78A Expired GB1568329A (en) | 1977-11-16 | 1978-02-16 | Circuit arrangement for loudspeaking telephone set |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5472906A (en) |
| CH (1) | CH626485A5 (en) |
| DK (1) | DK74878A (en) |
| FI (1) | FI780555A7 (en) |
| FR (1) | FR2409645A2 (en) |
| GB (1) | GB1568329A (en) |
| IT (1) | IT1161440B (en) |
| LU (1) | LU79026A1 (en) |
| NL (1) | NL7801820A (en) |
| SE (1) | SE7801902L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2194868A (en) * | 1986-09-02 | 1988-03-16 | Motorola Inc | Speakerphone with fast idle mode |
| US5544242A (en) * | 1993-05-25 | 1996-08-06 | Exar Corporation | Speakerphone with event driven control circuit |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8317706D0 (en) * | 1983-06-29 | 1983-08-03 | Standard Telephones Cables Ltd | Telephone subsets |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4051325A (en) * | 1975-01-31 | 1977-09-27 | Matsushita Electric Industrial Co., Ltd. | Speech intercommunication system |
| DE2638286C3 (en) * | 1976-08-25 | 1979-03-01 | Dasy Inter S.A., Genf (Schweiz) | Circuit arrangement for a hands-free telephone |
-
1978
- 1978-02-08 LU LU79026A patent/LU79026A1/en unknown
- 1978-02-16 GB GB6251/78A patent/GB1568329A/en not_active Expired
- 1978-02-16 FR FR7804396A patent/FR2409645A2/en active Pending
- 1978-02-17 NL NL7801820A patent/NL7801820A/en not_active Application Discontinuation
- 1978-02-20 IT IT12485/78A patent/IT1161440B/en active
- 1978-02-20 SE SE7801902A patent/SE7801902L/en unknown
- 1978-02-20 FI FI780555A patent/FI780555A7/en unknown
- 1978-02-20 JP JP1840878A patent/JPS5472906A/en active Pending
- 1978-02-20 CH CH182478A patent/CH626485A5/en not_active IP Right Cessation
- 1978-02-20 DK DK74878A patent/DK74878A/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2194868A (en) * | 1986-09-02 | 1988-03-16 | Motorola Inc | Speakerphone with fast idle mode |
| GB2194868B (en) * | 1986-09-02 | 1990-10-24 | Motorola Inc | Speakerphone with fast idle mode |
| US5544242A (en) * | 1993-05-25 | 1996-08-06 | Exar Corporation | Speakerphone with event driven control circuit |
Also Published As
| Publication number | Publication date |
|---|---|
| DK74878A (en) | 1979-05-17 |
| JPS5472906A (en) | 1979-06-11 |
| IT7812485A0 (en) | 1978-02-20 |
| SE7801902L (en) | 1979-05-17 |
| NL7801820A (en) | 1979-05-18 |
| IT1161440B (en) | 1987-03-18 |
| FI780555A7 (en) | 1979-05-17 |
| CH626485A5 (en) | 1981-11-13 |
| LU79026A1 (en) | 1978-06-21 |
| FR2409645A2 (en) | 1979-06-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed [section 19, patents act 1949] | ||
| PCNP | Patent ceased through non-payment of renewal fee |