DE1211270B - Circuit arrangement for a voice-controlled intercom or two-way intercom system with hands-free operation that is connected via a fork to a two-wire connection line - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H04m

H04b

German KL: 21 a2 - 36/02

Number:
File number:
Registration date:
Display day:

T 22268 VIII a / 21 a2

June 7, 1962

February 24, 1966

The invention relates to a circuit arrangement for a two-wire connecting line via a fork connected voice-controlled intercom system with hands-free operation with one with the microphone or speech amplifier in the transmission branch and one with the loudspeaker or hearing amplifier The speech or hearing amplification looped into the receiving branch in terms of alternating current regulating direct current controllable attenuator and one further such attenuator each.

Such circuit arrangements are known per se. For example, with a well-known Circuit made the arrangement so that behind the above-mentioned further attenuator Part of the transmit or receive AC voltage is branched off and one each to the transmit or receive branch individually assigned control amplifier with control rectifier fed to a bridge circuit that for voice-controlled speech direction switching the respective size of the transmission and which compares receiving AC voltages with one another and accordingly one such Direct current control for the four attenuators causes the two to correspond to the one discussed Branch associated attenuators conduct and deaden this quickly, while the two the block the attenuators assigned to the other unspoken branch and at least this quickly attenuate accordingly.

In this known arrangement, it is necessary that the in the transmit or receive branch lying attenuators have a large controllable attenuation range of about 50 db must be. These attenuators are set so that they are in the unspoken state of the arrangement have an average attenuation at rest, which is about 25 db. Attenuators with a such a high controllable damping range are difficult to produce. In particular, it needs special ones Measures to keep the damping present in the idle state largely constant.

The invention is based on the object of providing a circuit arrangement of the type described above to create that works reliably with the same effort and a faster reversal of the direction of speech and thereby avoids the disadvantages of the known circuit arrangement described above.

The solution to this problem is that each in front of the control amplifier of the Sendebzw. Another attenuator located in the receiving branch, also in series in terms of alternating current

Circuit arrangement for a connected via a fork to a two-wire connection line
voice-controlled intercom or intercom system with hands-free operation

Applicant:

Telefonaktiebolaget LM Ericsson, Stockhohn

Representative:

Dr.-Ing. H. Ruschke, patent attorney,

Berlin 33, Auguste-Viktoria-Str. 65

Named as inventor:
Lars Gunnar Ulin, Stockholm

Claimed priority:
Sweden, June 8, 1961 (6007)

The transmission or reception branch is located, and both with their DC control input are antiparallel to one another are connected, and that the two attenuators assigned to the transmission branch for the they in the receiving state blocking control direct current in the transmission direction to the microphone in series are switched, while the attenuators assigned to the receiving branch are in the transmitting state for them blocking DC control current are connected in series in the forward direction to the loudspeaker.

In this circuit arrangement, the attenuators only need to have a maximum attenuation which is half as large as the attenuation range in the known circuit arrangement. As a result, the attenuators used in the subject matter of the invention can be controlled with smaller currents, so that the control part of the circuit arrangement can be constructed in a correspondingly simpler manner.
Since only end states have to be controlled in the case of the attenuators, namely the state without attenuation and the state of maximum attenuation, these end states can also be passed through

609 509/244

1-211 27 O

Establish overdrive, so that there is also a considerable increase in the switching speed results. In contrast, in the known circuit arrangement, a third one must be between the end states lying state can be set, which cannot be established by overdriving.

The invention is described in more detail below with reference to the drawing.

F i g. 1 shows a circuit arrangement according to the invention;

Fi g. 2 shows a circuit diagram for two current controlled Attenuators of the circuit arrangement according to il

Fig. 3 shows schematically drawn out the parallel and series connection of the control DC inputs of the four attenuators that are included in the circuit arrangement according to Fig.l, and

4 shows the magnitude of the direct control currents for the attenuators. in dependence on the respective difference of occurring at the outputs of the bridge circuit voltages derived Ul and U. 2

As Fig. 1 shows, the speech alternating currents generated during speak into a microphone M are amplified in a preamplifier Fl and passed through in the transmission state at least attenuating first attenuator Dl, a post-amplifier F 3 and a fork IL2 to a two-wire line L in a known manner .

A control amplifier TrI with a rectifier is connected in a known manner to the transmission branch via a further, third attenuator D 3, which derives a corresponding control direct current for the attenuators from the alternating speech current occurring in each case.

In the same way, at the beginning of the reception branch, before the second attenuator Ό 2 - to which the loudspeaker H is connected via a hearing amplifier F 2 - via a further (fourth) attenuator D 4, a control amplifier Tr 2 for the control amplifier TrI of the transmission branch is connected to it the receiving branch connected in a known manner.

In the known circuit arrangement, the further attenuator D 3 or D 4 upstream of the control amplifier is connected in terms of alternating current in parallel to the first or second attenuator D1 or D 2 , which is designed as a longitudinal attenuator, and its control DC input is connected to the second or first attenuator D 2 or Dl of the other branch connected in series to its control amplifier.

In contrast, in the embodiment of FIGS. 1 and 2, all four attenuators Dl formed as a cross-attenuators to D 4, and according to the invention is each respectively in front of the control amplifier TrI, Tr 2 of the transmitting and receiving branch lying further attenuator D 3, D 4 in terms of alternating current also in series in the transmitting and receiving branch, and both are connected to one another in antiparallel with their direct current control input 31, 32, 32 '. The two attenuators D1 and D 2 assigned to the transmission branch are connected in series in the transmission direction to the microphone M for the control direct current which blocks them in the reception state, while the attenuators D 2 and D 4 assigned to the reception branch for the control direct current which blocks them in the transmission state in the transmission direction to the loudspeaker H. are connected in series.

Each additional attenuator D 3 (see Fig. 2 or D 4) consists of an input transformer T 5, the secondary winding of which has a central tap 31 or 31 ', of two mutually connected rectifiers L 31 and L 32, which are the ends of the secondary winding of the input transformer Γ 5.

The first and second attenuator Dl or D 2 consists of an output transformer T 6, the primary winding of which is a middle one. Tap 36 and 36 'and two rectifiers LU and L 12, also connected against each other, which bridge the ends of the primary winding of T 6 and also via a resistor Rl or R2 to the ends of the secondary winding of the input transformer of the further attenuator D3 and D, respectively 4 are connected.

The current-controlled attenuators are influenced in a known manner by the control direct currents flowing through them, in such a way that they dampen their branch more strongly with a larger control direct current, and in the unspoken quiescent state, the first attenuators Dl and D 2 receive a quiescent control direct current, so that they have a Have idle attenuation of, for example, 25 db, with which they attenuate their branch, ie keep it half unlocked and half locked. In contrast to

; .. of the known circuit arrangement, the second attenuators D 3 and D 4 in the idle state in the invention do not receive any control direct current and are therefore completely unlocked (O db).

In a preferred embodiment of the invention, the connection points are on the one hand between the attenuators connected in parallel or in series with their DC control inputs and on the other hand the wires of the control DC inputs facing away from the connection points of the first attenuators, i.e. the outputs of the bridge circuit, each have equal resistances connected to a point with a fixed negative potential.

The circuit arrangement according to the invention can advantageously also be constructed so that the both outputs of the bridge circuit individually with the control amplifier via the primary winding each of a transformer are connected, the secondary winding of which each has a center tap that is connected to the input side of the other control amplifier is connected, while the two ends of the secondary windings via rectifier to the midpoint of a consisting of fixed resistors Voltage divider are connected.

In the known control circuits, the attenuators D1 and D 2 generally have to be controlled according to a specific curve so that they are set to 25 decibels in the idle state, 50 decibels in the working position and 0 decibels when transmitting or receiving. A particular advantage of the circuit arrangement according to the invention is that only the following conditions must be met: In the idle state, the attenuators Dl and D 2 are set to 25 decibels and the attenuators D 3 and D 4 to 0 decibels, while D 3 and Dl must have 0 decibels and D 4 and D 2

25 decibels each. Such a scheme according to the principle the "either-or" circuit of electronic computing devices is technically much simpler feasible than the earlier solutions to this problem.

The mode of operation of the circuit arrangement according to the invention is as follows:

The amplifier arrangement is in the idle state, that is, no speech currents are applied to the amplifier Fl and F2, the transistors TrI and Tr2 perform equally large central rest DC control currents whose thickness is, for example, each 1 mA. The voltages at points 1 and 2 are equal in this case, and due to the equality of the direct control currents, the same control direct currents only flow in the attenuators D 1 and D 2, but not through the attenuators D 3 and D 4. Oil in the attenuator For example, the control direct current flows in the following way:

1, 36, T6, L11 / 12, 35, 32, 3, RlS, -.

The attenuators D 3 and D 4 do not receive any control currents in the idle state, because in this case points 3 and 4 have the same potential. This operating state is achieved with all the clarity of FIG. 3. In the same potentials at the points 1 and 2 indicate the same DC control currents through D1 and D2 via the resistors RlS and R16, and because these resistors are equal, also the potentials at the points 3 and 4 are the same size, ie no direct control currents flow through the attenuators D 3 and D 4. This operating state (idle state) is indicated in FIG. 4 by the ordinate Ul = U2 , where Ul is the potential at point 1 and U 2 is the potential of point 2 means. The direct control currents through the attenuators D1, D 2, D 3 and D 4 are designated here by il, i2, / 3 and / 4. As you can see, H = i2 and thus i, while / 3 is roughly equal to ζ 4 and roughly equal to 0.

If the circuit arrangement is switched to transmit, ie speech currents are fed into the two-wire line L from the microphone, then a certain proportion of these speech currents is branched off in a known manner via the line 33/34 and the transformer Π to the control amplifier (transistor) TrI. The speech currents amplified by the control amplifier are rectified in a circuit which consists of the secondary winding of a transformer Γ3, rectifiers Ll and L2, a resistor .R12 and a capacitor C 2. The center tap on the secondary windings is raised to a negative potential with respect to the voltage divider center point 5, and this negative potential is passed through the secondary winding of the transformer Γ2 to the base of the transistor Tr 2 acting as a control amplifier.

In the same way, when switching to receive, the increased negative potential of the center tap of the secondary winding of the transformer T 4 compared to the voltage divider center point 5 is fed to the base of the transistor TrI acting as a control amplifier via the secondary winding of the transformer Tl.

The change in the negative potential at the base of the transistor 7V2 results in an increase in the current through this control amplifier, which is expressed in an increase in the potential of point 2 and in an increased potential drop at the emitter series resistor RU , which the two transistors TrI and Tr 2 is common. The resulting increase in the negative potential at the emitter of the transistor TrI thus causes a reduction in the current through the transistor TrI. As a result, point 2 has an even higher potential than point 1,

ίο ie t / 2 greater than Ul, and not only the attenuator D 2 continues to receive its control direct current i 2, but now also the attenuator! ^, while the attenuator Dl no longer receives any control direct current or only receives a smaller control direct current il, which against Zero decreases. As a result, the speech currents generated by the microphone can reach the two-wire line L without difficulty, while the speech currents coming out of the line cannot reach the loudspeaker H.

If the arrangement is switched to receive, ie the speech currents come from the line L, then a certain proportion of these receive alternating voltages is conducted in a known manner via the line 43/44 and the transformer Γ 2 to the transistor Tr 2 . In the same way as described above, the direct current through the transistor Tr 2 decreases, while the direct current through the transistor TrI increases; the point 1 comes to a higher potential than the point 2, ie Ul is greater than i / 2, and the attenuators Dl and D 3 receive their control direct current, while the attenuator D 2 receives only a control direct current which decreases towards zero. The following circuit then exists for attenuator D 3:

3/32, L31 / L32, Γ 5, 31, 4.

The attenuator D 4 does not carry a direct current control, because in this case point 3 is at a higher potential than point 4. As a result, the AC received voltages from the two-wire line L reach the loudspeaker H, while the speech currents possibly generated by the microphone M reach the line L cannot reach.

The respectively stronger alternating speech voltage asserts itself in a known manner in that the direct current control current derived therefrom undampes the branch under discussion and attenuates the other branch to which weaker or no alternating speech voltages are applied. Since, just like in the known arrangement according to German Auslegeschrift 1086 753, the second attenuator D 3, D 4 upstream of each control amplifier is controlled by the direct control currents in the sense of an amplification of the direction switching already initiated by the stronger voice alternating voltages, the result is the same as with the above known arrangement, a very rapid speech direction switching and in the unspoken branch an increased attenuation, which thus in turn brings with it an increased dynamic and a lower distortion.

In the above known arrangement, in contrast to the AB, the further attenuator D 3, D 4 upstream of each control amplifier is not in series in the branch before its first attenuation

member, but is branched off in parallel in front of this and is controlled by the control amplifier of the other discussed branch derived control direct current switched to higher attenuation, so that the downstream control amplifier of the unspoken branch supplies a smaller DC control current that supplies the first attenuator of its branch to higher attenuation and the second Attenuator of the other branch discussed switches to even lower attenuation. Through this the downstream control amplifier of the branch discussed provides an even larger one Control direct current, which leads to the mentioned very rapid switching of the speech direction.

In contrast to this known arrangement, the second according to the invention Attenuators placed alternately in series in their branch and the first and second Attenuators of each branch are therefore not allowed to have their attenuation in opposite directions within their branch change,

A significant simplification of the aforementioned known arrangement results from the fact that, for the aforementioned reason, the two attenuators of each branch are connected in series with their control DC input for the control direct current supplied only by the control amplifier of its branch, which is then transferred from the mean quiescent value in the respective branch discussed to one of these The unlocking value is reduced so that the part of the speech alternating voltage amplified in the control amplifier (e.g. Tl) of the branch discussed is fed rectified to the base of the other control amplifier 2V2 of the respective unchecked branch, the control current of which thereby changes from its quiescent value to the second attenuator D 4 of an unspoken branch blocking value is increased and on the other hand, due to the increased voltage drop across the common emitter resistor R 11 shifts the operating point of the control amplifier TrI of the branch discussed in such a way that its control equilibrium chstrom is reduced from the rest value so far that the first attenuator D 1 of the branch discussed is undamped or unlocked, while the second attenuator D 3 of the branch discussed retains this undamped state, which was already in the idle state.

On the other hand, as is known, the switchover from the transmit or receive state to the unspoken idle state should take place relatively slowly in order to avoid too frequent switching to the idle state during pauses in speech. This is achieved in a manner known per se by the interaction between the capacitor C 3 (or the capacitor C 4 for the opposite direction of speech) and a series connection of a resistor 2218 and a capacitor C 5 between point 1 and the upper terminal of the capacitor Cl (or a series connection of a resistor R 19 and a capacitor C 6 between point 2 and the upper terminal of the capacitor Cl).

When the receiving AC voltages cease, the DC voltage at the collector of the transistor TrI initially drops very quickly as a result of the capacitor C 3 to a level which is slightly higher than the level which causes the regulation of the damping circuits in question. Then the DC voltage at the collector falls slowly as a result of the series connection R 18, C 5 to that level which corresponds to the idle state of the arrangement.

Claims (3)

Patent claims: 1. Circuit arrangement for a connected via a fork to a two-wire connection line voice controlled counter or ίο Two-way intercom system with hands-free operation with a microphone or speech amplifier in the transmission branch and one in the loudspeaker or hearing amplifier in the receiving branch switched on with an alternating current, the speech or hearing amplification regulating direct current controllable ■ attenuator and each other such. AC reception voltage is branched off and fed via a control amplifier with control rectifier individually assigned to each of the transmission and reception branches to a bridge circuit, which compares the respective magnitudes of the transmission and reception AC voltages with each other for voice-controlled speech direction switching and accordingly causes such DC control currents for the four attenuators that the two The attenuation elements assigned to the branch discussed in each case have the effect that the two attenuators assigned to the branch discussed in each case conduct and rapidly de-attenuate it, while the two attenuators assigned to the respective other branch that are not discussed block and at least rapidly attenuate it at least correspondingly, characterized in that: that each in front of the control amplifier (TrI, Tr 2) of the transmitting or _{receiving branch Emp T} lying further attenuator D 3, D 4) alternating current is also in series in the transmitting or receiving branch, u nd both with their DC control input (31, 32, 32 ') are connected in antiparallel to one another, and that the two are assigned to the transmission branch. Attenuators (Dl, D 3) for the DC control current blocking them in the receiving state are connected in series in the transmission direction to the microphone (M), while the attenuation elements (D 4 and D 2) assigned to the Speakers (H) are connected in series. 2. Circuit arrangement according to claim 1, characterized in that on the one hand the connection points (3, 4) between the attenuators connected in parallel or in series with their control DC inputs and on the other hand the cores (36, 36 ') facing away from the connection points (3, 4) ) the control DC inputs of the first attenuators (D 1, D 2), i.e. the outputs (1, 2) of the bridge circuit, are connected to a point with a fixed negative potential via resistors of the same size (R15, R16 or R14, RIT). 3. Circuit arrangement according to claim 1 or 2, characterized in that the two outputs (1, 2) of the bridge circuit individually with the control amplifiers (TrI or Tr 2) via the primary winding each of a transformer (T3 or Γ 4) are connected, the secondary winding each having a center tap that is connected to the input side of the other control amplifier (Tr 2 or TrI) , while the two ends of the secondary windings each via a rectifier (Ll to L 4) the middle 10 point (5) of a voltage divider consisting of fixed resistors (R13, R12) are connected. Documents considered: German Auslegeschrift No. 1086 753. 1 sheet of drawings 609 509/244 2.66 © Bundesdruckerei Berlin