Hybrid circuit

Holder: Idem (7d) (74) Agent: Georges Souquet, SPID Civil Society, 209, rue de l'Université, Paris (7)

Terminator for coupling bidirectional transmission channels to unidirectional channels.

Invention of:

33) (32) (31

Conventional priority: Patent application filed in the Netherlands on January 13, 1970, n. 70 / 00.395 in the name of the plaintiff.

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The invention relates to a terminator for coupling a bidirectional transmission channel to a unidirectional transmission channel and to a unidirectional reception channel; this terminator comprises a first amplifier whose input is connected to the reception channel and the output to the bidirectional transmission channel, a second amplifier whose input is connected to the bidirectional transmission channel and the output to the communication channel transmission and a third amplifier whose input is connected to the reception channel and the output to the transmission channel.

One such terminator is described in U.S. Patent No. 2,511,948.

The invention provides a terminator of the type envisaged in the preamble, suitable for balanced transmission of voice signals, for hook and selector dial signaling, and for call signaling as well as for the power supply method of lines used with subscriber lines to which conventional subscriber devices are connected, with protection against induction voltages in the subscriber lines.

The terminator according to the invention is characterized in that the second amplifier is a differential DC voltage amplifier and in that the first amplifier has a balanced output coupled for DC voltage and in that between the bidirectional transmission path and the input of the second amplifier is connected to a damping circuit.

The description which follows, with reference to the appended drawings, will make it clear how the invention can be implemented.

Fig. 1 shows an embodiment of the terminator according to the invention.

Fig. 2 is an equivalent diagram.

Fig. 3 shows an embodiment of a ccmmutable current source.

Fig. 1 shows a transmission line T in which signals are transmitted in both directions. In this example, the transmission line T is a subscriber line. On the other hand, fig. 1 represents a unidirectional transmission line 0, by which signals are transmitted to the terminator and a unidirectional transmission line 2 by which signals are transmitted from the terminator. These lines respectively form the reception channel and the transmission channel of a so-called 5.4-wire link.

Reception channel 0 is connected to the input of an amplifier—

00964 ficitor 10 and at the input of an amplifier 20. The subscriber line T is connected to the output of the amplifier 20 and is connected, via a damping circuit 40, to the input of an amplifier 30. The output of amplifier 30 and the output of amplifier 10 are both connected to the transmission channel Z. Amplifier 10 provides a signal at the output such that the signal which appears successively through amplifier 20, damping circuit 4θ of amplifier 30, on the transmission channel 2 is compensated.

The amplifier 20 consists of the transistors 21 and 22, the emitters of which are connected, by means of identical emitter resistors 23 and 24, to the output 25 of a switchable current source 26. The control input 29 of this current source is connected to the reception channel 0. When the signal which is received from the reception channel 0 exceeds a certain amplitude threshold, the current source 26 is switched on.

When switched on, the current source 26 supplies a constant current Ig from the point of connection of the emitter resistors 23 and 24 to a power point brought to a voltage of -Vbg volt. The collector of transistor 21 is connected, via a collector resistor 27 to a power point brought to a voltage of + Vb ^, with, for example, Vh ^ = Vhg. The collector of transistor 22 is grounded via a collector resistor 28. The first conductor of subscriber line T is connected to the collector of transistor 21 and the other conductor is connected to the collector of transistor 22. The collector resistor 27 has the same ohmic value as the collector resistor 28. La. subscriber line T receives, via these resistors, a balanced power supply with DC voltage, as is desirable for powering the microphone and hook signaling of conventional subscriber telephone sets.

Amplifier 10 consists of transistors 11 and 12, the emitters of which are connected, by means of identical emitter resistors 13 and 14, to a current source I5. This current source delivers a constant current from the point of connection of the emitter resistors 13 and 14 to a power point brought to a voltage of -Vbg volt. The collector of transistor 11 is connected to a power point brought to a voltage of + Vb ^ volt. The collector of transistor 12 is connected to the conductor which is not grounded, of the emission channel Z.

The base electrodes of transistors 21 and 11 are

00964 interconnected and are connected, via a capacitor 5θ> to the conductor which is not grounded, of the reception channel 0. The base electrodes of transistors 22 and 11 are interconnected and are connected to ground via capacitor 51 · the basic bias voltage for transistors 11 and 12 and 21 and 22 is taken from a worn supply point at a voltage of -Vb ^ volt, with for example -Vb ^ = -Vb ^ + 4 volts, which is connected, via resistors 52 and 53, to the base electrodes of transistors 11, 21 and 12, 22 , respectively.

Amplifier 30 consists of transistors 31 and 32, the emitters of which are connected, by means of identical emitter resistors 33 and 34, to a current source 35 · This current source delivers a constant current 1 ^ of the connection point of resistors 33 and 34 to a supply point brought to a voltage of -Vb ^ volt. The collector of transistor 31 is connected to a power point brought to a voltage of + Vb ^ volt. The collector of transistor 32 is connected, via a collector resistor 36, to a power point brought to a voltage of + Vb ^ volt. This collector is also connected to the capacitor which is not grounded, of the emission channel Z, this latter conductor also being connected to the collector of transistor 12.

The conductors of the subscriber line T are connected, via resistors 41 and 42 of the damping circuit 40, to the base electrodes of transistors 31 and 32. Between these base electrodes are connected in series the resistors 43 and 44 of the damping circuit 40. The painted connection of the resistors 43 and 44 is connected to a supply point brought to a voltage of -Vb ^ volt, for the supply of a basic bias voltage to the transistors 31 and 32.

Amplifier 20 converts the unbalanced signal from the reception channel 0 into a balanced signal on the subscriber line T. Amplifier 30 converts the balanced signal from the subscriber line T into a unbalanced signal on the transmission channel Z. The terminator is thus adapted to the conventional form of signal transmission by subscriber lines.

Amplifier 30 has a differential input and is only sensitive to signals which introduce differences between the base current of transistor 31 and the base current of transistor 32.

Disturbances induced in the subscriber line T by nearby strong current networks or by lightning, cause longitudinal currents in the subscriber line T. These currents have the same intensity

00964 and the same direction in the two conductors of the subscriber line T and similarly influence the transistors 31 and 32. Variations in base voltages of the transistors 31 and 32 which have the same phase are not amplified, given that the effective emitter resistance of the transistors is very high for such variations, due to the use of the current source 35 ·

The damping circuit 40 connected between the subscriber line T and the input of the amplifier 30 weakens the disturbances and protects this amplifier 30 against the appearance of excessively high voltages at the input.

The amplifier 30 is a DC voltage amplifier so that signals with the hook and the selection dial of the telephone apparatus connected to the subscriber line T, can be detected on the transmission channel Z. The signals of selection according to the method with which resistors are inserted into the subscriber loop by means of push buttons, can be detected in the transmission channel Z. The variations in polarity of the subscriber line supply voltage used with this selection method can be obtained by completely saturating one or the other of the transistors 21 and 22 using an applied signal. at reception channel 0.

The amplifier 20 can apply to the subscriber line voltages having an amplitude of the order of magnitude of the supply voltage of + Vb ^ volt, under the control of signals applied to the reception channel 0. The ce In fact, it is possible to activate, via the terminator, a conventional calling device, namely an AC bell connected to the subscriber line.

The current source 26 is switched off when the reception channel 0 is in the state for which no signal is applied to it. In this rest state of the reception channel 0, the amplifier 20 has a very low dissipation. A terminator produced in practice had a rest dissipation of less than 100 mW.

By choosing a capacitance for the capacitors 5θ and 51 such that the impedances of these capacitors are small compared to the resistors 52 and 53, it is possible to obtain an amplitude-frequency characteristic of the transmission path to the subscriber line T, which s 'practically extends up to OHz. The amplitude-frequency characteristic of the subscriber line T to the transmission channel Z includes the frequency of 0 Hz, since between them is connected a DC voltage amplifier.

A circuit with a transmission characteristic

00964 which begins at around 0 Hz and a range of amplitudes from very small amplitudes to very high amplitudes, the latter possibly being of the order of magnitude of the supply voltage, is called transparent circuit. For all practical applications the terminator shown in fig. 1 is a transparent terminator. Such transparent terminators can advantageously be used in the peripheral devices of electronic telephone systems with wire link channels.

Fig. 2 represents the equivalent diagram of the terminator of FIG. 1 allowing to deduce approximately the equilibrium condition.

The amplifier 10 is replaced by an Ohms input resistance and an output current source delivering a current of 1 ampere. R '^ = bR ^ and i' ^ "= bi ^, b being the current amplification factor, R ^ the sum of the ohmic values ​​of the emitter resistors 13 and 14 and i ^ the current through the resistor d 'Entrance. Amplifiers 20 and 30 are similarly replaced by an input resistor and an output current source. The resistance of R Ohm replaces

V the input impedance of the subscriber line T as seen from the terminator. The resistance of R ^ Ohm replaces the collector resistors 27 and 28. The resistance of R Ohm replaces the input impedance of

Z the transmission channel Z as seen from the terminator. The damping factor of the damping circuit 40 is represented by at.

The voltage source supplying the voltage replaces the reception channel 0 to which a signal is applied.

From the equivalent scheme and from what we said above we can deduce the following relationships:

from R 'bi be = b e_

R. b_Rl e

R.

(1) in the same way as in (1):

i '= e_ ^R2 ^V2 = ⁱ2

aV,

Rb.Rt

Rb + Rt '3 “*' 2 in the same way as in (1):

i '= V 13 _ v₃ (2) (3) (4) (5)

The substitution âe (2), (3) and (4) in (5) provides:

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Rb.Rt

Rb + Rt (6)

In the equilibrium state, we must have:

This condition is satisfied if:

We deduce from (l) and (6) the equilibrium condition:

at . Rb.Rt = R3.R2

Rb + Rt R₁ (7)

When the subscriber line T has a characteristic resistance Ro and when the subscriber line is closed by the characteristic resistance and if, on the other hand, Rb = Ro, the equilibrium condition (î) is reduced to:

a Ro = R3.R2 (8)

When the subscriber line has a characteristic impedance

Zo which is not a resistance, condition (8) remains valid if Ro is replaced by Zo, when the collector resistances, 27 and 28 of fig. 1 are replaced by Zo / 2 impedances. The equilibrium condition can be satisfied by inserting into the transmitter circuits, transistors 21 and 22 or 31 and 32 complex impedances proportional to Zo.

Fig. 3 shows an exemplary embodiment of the switchable current source 26 of FIG. 1. The current source comprises a transistor η — p — n 54 whose collector is connected to the output 25 and whose emitter is connected, via an emitter resistor 55, to a supply terminal 5 ^ · The base electrode is connected, via a base resistor 57, to the supply terminal 56 and it is connected, via a base resistor 5θ, to the collector a pnp transistor. The emitter of this transistor is grounded. The base electrode is earthed via an RC network 60 and it is connected to the control input 29 via the base resistor 61. When at the control input 29 is applied a control signal which exceeds the emitter-base threshold voltage of the transistor 59, the transistor 57 outputs a collector current. This collector current fulfills the basic current function for the transistor 54 · When the control signal has a sufficient amplitude, the transistor 54 is brought to saturation by the collector current of the transistor 59- In this state, the transistor 54 delivers a practically constant current, from the output 25 towards the supply terminal 56. The resistors

00964 in the emitter and base circuits of transistor 54 fulfill the function of elements determining the current.

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