CH618557A5 - Telephone installation including for each telephone set a device for transmitting and receiving coded telephone pulses - Google Patents

Abstract

The device includes a modulation path, a demodulation path, and electronic switchgear. The demodulation path includes an active filter of the SALLEN KEY type with TSCHEBYSCHEV behaviour, preferably of order six with a low-pass response curve, producing compensation for the distortion as (sin omega tau 2)/ omega tau 2 which is due to the demodulation, omega being the angular frequency of the low-frequency signal and the width of each sampling signal. This arrangement makes it possible to eliminate the demodulation distortion very effectively. The active filter (FAD) represented includes an input stage with operational amplifier (2) and three structures of the SALLEN KEY type of second order each including an operational amplifier with low consumption. The modulation path and the demodulation path are connected to a set by way of a line and of switchgear for the transmitted and received signals culminating respectively at a modulator and at a demodulator. The semi-conductor electronic switchgear possesses three pairs of poles, one of which is joined to the telephone set and the other two of which are joined to the modulation and demodulation paths respectively. <IMAGE>

Description

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CLAIM The main patent 583 484 relates to a remote installation

Telephone installation according to the claim of the phonic patent comprising for each telephone set a provision

main, characterized in that the competitive demodulation channel for transmitting and receiving telephone pulses takes an active filter of the so-called SALLEN KEY type, with a coded one, comprising a modulation channel and a response curve channel of the low-pass type, producing a demodulation compensation connected to a telephone set by means of

..... ,. cûTmCdt • j -, ji diary of a line and a signal switching element of the distortion in (sm ^) / -r, which is due to the demodula- „, ..„. . . °.

v 2 'l M and received respectively leading to a modulator and a tion, tu being the pulsation of the low frequency signal, and x, the demodulator. According to the claim of this patent, the width element of each sampling signal. is a semiconductor electronic turnout with

io three pairs of poles, one of which is joined to the telephone set

SUB-CLAIMS that, the other two being respectively connected to the

1. Installation according to claim, characterized in that modulation and demodulation.

ie the active filter of the demodulation channel comprises three structures. The installation according to the present invention is characterized in res of the so-called SALLEN KEY type of the second order, since [a demodulation voje comprises an active filter of the type each having a operational amplifier, low consumption called SALLEN KEY, with a response curve of the tion type, and being connected in series, preferably so that the low-pass, producing a distortion compensation in output structure has a higher overvoltage coefficient • <ox oox •

laughing at that of the input structure, and lower than that of the ~ 2 ~ V which is due to demodulation, tu being the pulsation median structure. of the low frequency signal, and t, the width of each signal

2. Installation according to sub-claim 1, characterized in: o sampling.

that the input structure is preceded by an amplifier SeIon an embodiment of the device described in operational, which is mounted as an active attenuator, and whose main patent gain, each of the modulation and demo channels

is adjusted according to the gains of the amplifiers of the three dulation may include an active filter, acting as a filter and SALLEN KEY structures. amplifier, modulation or demodulation.

Various alternative embodiments of the present invention

3. Installation according to claim or 1 one of the sub-relate to active modulation and demodulation filters, claims 1 and 2, characterized in that the output of the demo a; nsi qUe of the electronic switcher, which are provided in the dulator, in particular one of the armatures of the capacitor-device described in the main patent.

corresponding tank, is coupled to 1 input of the active filter of Qn described in the main patent an embodiment the demodulation path by a capacitor mounted in series. 30 of the active demodulation filter, of the so-called SALLEN KEY type,

4. Installation according to claim, characterized in that with a behavior of TSCHEB YSCHEV. According to the pre-

1 electronic switch has an adaptation resistor, it is an invention using an active demodulation filter, equal-inserted between the demodulation channel and the line, as well as a ment of the SALLEN KEY type, preferably of order six, but operational amplifier, having its output connected to the channel with a low-pass response curve, producing a modulation, a first input, connected to the demodulation channel 35 WT wx tion through a network for compensating for variations in impedance of the distortion in (sin -j -) / -j-, which is due to the line dance, and a second input, connected to a demodulation point (co being the pulsation of the low frequency signal,

through a voltage divider inserted between the line and the and T> the width of each sampling signal). This perfec-output of said operational amplifier, said intermediate operating point is particularly advantageous insofar as it is from the voltage divider being chosen so that a signal arriving by ™ makes it possible to very effectively eliminate demodula distortion-the demodulation path does not produces a practically zero voltage at the output of the operational amplifier.

5. Installation according to sub-claim 4. characterized in In a preferred embodiment, the active filter that the compensation network comprises two demodulation cells comprises three structures of the type known as S AL-type R — C, mounted in series, which can be adjusted separately- 45 LEN KEY of the second order, each comprising an amplifier to act one at low telephone frequencies, and operational cator with low consumption, and being mounted in the other at high telephone frequencies . series, preferably so that the output structure

6. Installation according to sub-claim 5, characterized in that has an overvoltage coefficient greater than that of which each cell is constituted by a branch in series of the input structure, and less than that of the median structure, type RC in parallel, followed by resistance in parallel. 50 Preferably, the input structure is preceded by an amplifier

7. Installation according to claim or any operational cator, which is mounted as an active attenuator, and of which of sub-claims 1 to 6, characterized by the use of amplifier - the gain is adjusted according to the gains of the amplifiers operational ficers with adjustable electrical consumption, with three SALLEN KEY structures.

using in particular resistors with adjusted values. According to another embodiment, the electronic signalman

8. Installation according to claim, characterized in that 55 comprises an adaptation resistor, inserted between the channel of each of the active modulation and demodulation demodulation filters and the line, as well as an operational amplifier, comprises an operational amplifier and in that having its output connected to the modulation channel, a first means, such as operational amplifiers of the input filters, connected to the demodulation channel through a network of modulation and demodulation assets, for adjusting the compensation voltage variations in line impedance, and an offset of said operational amplifier so as to obtain 60 second input, connected to an intermediate point of a divider of a very low direct voltage on the output of the active voltage filter, inserted between the line and the output of said corresponding amplifier. operational, said intermediate pin of the voltage divider

Installation according to claim, characterized in that being chosen so that a signal arriving by the demodula channel - the input of the active modulation filter is coupled to the output tion produces only a practically zero voltage at the corresponding output of the electronic switch by a capacitor fi5 the operational amplifier. In this way, the incoming signal connected in series. By the demodulation v ° ie is transmitted, through the adaptation resistor, to the line, under a suitable impedance, while the output of the operational amplifier only transmits

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hardly any signal at the modulation channel. The operational amplifier of the switcher on the other hand transmits a signal arriving by the line, to the modulation channel, with a determined gain and a frequency correction which makes it possible to compensate for the variations in the electrical characteristics of the line. - 5

In a preferred embodiment of the electronic switch according to the present invention, the compensation network comprises two cells of the RC type, connected in series, which can be adjusted separately to act one at low telephone frequencies, and the other at high telephone frequencies. Preferably, each cell is constituted by a branch in series of the R-C type in parallel, followed by a resistor in parallel.

Various means have also been described in the main patent for reducing the electrical consumption of the device for transmitting and receiving coded telephone pulses and in particular for limiting the electrical consumption of the various circuits when they are not operating. Various arrangements are also proposed here which make it possible to reduce the consumption of each of the different circuits of the device, while adapting it to the optimal operating conditions of the corresponding circuit, and this without however obliging to give up making the various circuits, and in particular the operational amplifiers which they comprise, in the form of standardized integrated circuits, preferably of a single type, with low consumption. For this, use is made, according to the present invention, of operational amplifiers with adjustable electrical consumption, notably using resistors with adjusted values. The same, standardized type of operational amplifier can thus be used to constitute, for example, the electronic switch and the active modulation and demodulation filters of the device according to the present invention, the consumption of each operational amplifier being adjusted. at least compatible with proper operation of the corresponding circuit, by means of an appropriate adjustment of the adjustment resistors35 of the electrical consumption of said operational amplifier.

The electrical consumption, in particular at rest, of each of the active modulation and demodulation filters of the device according to the present invention can be further reduced by associating means, such as resistors with adjusted values 411, with at least one of the operational amplifiers of said active filters, for adjusting the offset voltage of said operational amplifier so as to obtain a very low DC voltage on the output of the corresponding active filter; this obviously results in a very low consumption of electrical energy 45 continuous in the impedance which is connected to the output of said active filter.

By way of example, there has been described below and illustrated diagrammatically in the accompanying drawing, a form of embodiment of the installation according to the present invention.

Figure 1 is the electrical diagram of an embodiment of an active demodulation filter belonging to the installation.

FIG. 2 represents the electrical diagrams of a J5 embodiment of an electronic switch and an active modulation filter.

In FIG. 1, the same reference, 47, has been designated as in FIG. 9 of the main patent, the input terminal of the active demodulation filter, FAD, of a device according to the invention. 60 This input terminal 47 of the active demodulation filter, FAD, is connected, by means of a coupling capacitor, 1, connected in series, on the one hand, to an omnibus demodulation line, OD (not shown), and, on the other hand, to one of the armatures of a reservoir capacitor, 102, the other armature of which is (, 5 connected to ground, and which constitutes the demodulator; in other words , the periodic pulses, amplitude modulated, which are transmitted by the demodulation bus line, OD, are

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stored in the reservoir capacitor 102, the charge voltage of which consequently varies, over time, along a staircase curve, the AC component of which is transmitted by the coupling capacitor 1 to the input terminal 47 of the active FAD filter.

The embodiment of the active demodulation filter, FAD, which is shown diagrammatically in FIG. 1, comprises an input stage, essentially constituted by an operational amplifier, 2, with low electrical consumption, preferably of a standardized type, for example of the type known under the designation 776. The operational amplifier 2 is mounted as an active attenuator; its negative input is connected to the input terminal 47 of the FAD filter via a resistor 3, of appropriate value, while its positive input is connected to ground via a resistor 4. Through to the coupling capacitor 1, no direct voltage, possibly transmitted by the demodulation omnibus line OD, can disturb the operation of the operational amplifier 2. A feedback resistor 5 is connected between the output of the operational amplifier 2 and its negative entry. On the other hand, the operational amplifier 2 is chosen of a type with adjustable electrical consumption, using in particular a resistor 6, the value of which is adjusted to give said operational amplifier 2 the minimum consumption, which is compatible with good operating conditions of the input stage of the active filter FAD. The operational amplifier 2, as well as the resistors 3 to 6, preferably constitute an integrated solid circuit, in which the resistors are embodied for example, in a manner known per se, by resistive ribbons; the value of the resistor 6 can in particular be adjusted, for the purpose indicated above, by an appropriate adjustment of at least one of its transverse dimensions, for example by the action of a beam of laser radiation, controlled by a device automatic.

The next three stages of the active filter FAD, which are connected in series with each other, and with the input amplifier stage 2 to 6, each include an operational amplifier, 7a, 7b or 7c, which can be of the same type as the operational amplifier 2. Each stage further comprises five resistors such as 8a to 12a, and two capacitors, such as 13a and 14a, which are connected to the positive and negative inputs of the corresponding operational amplifier, for example 7a, and at its output so as to constitute with it a structure of the so-called SALLEN KEY type of the second order, the overvoltage coefficient of which is determined by the values chosen for the various components 8a to 14a. The three SALLEN KEY structures, mounted in series, have their components chosen so that the output structure, 7c to 14c, has a higher overvoltage coefficient than that of the input structure, 7a to 14a, and less than that of the median structure, 7b to 14b. Each of the three SALLEN KEY structures being of order 2, their series connection constitutes an active filter of order 6, which presents a response curve of the low-pass type, producing compensation for the distortion in (sin ^) / Sp, which is due to demodulation (œ being the pulsation of the low frequency signal, and t, the width of each sampling signal). Thanks to these characteristics of the active demodulation filter, FAD, according to the present invention, the filtered and amplified signal which appears on the output line 15 of the active filter FAD has very low distortion.

The active filter constituted by the three SALLEN KEY structures, previously described, has an "amplitude / frequency" curve, which can be adjusted by varying, for example as indicated previously, the values of at least some of the resistive components of the three structures, so as to compensate for possible deviations, with their set values, capacitive components, such as 13a and 14a, and parameters

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operational amplifiers such as 7 a, and thus obtaining the desired "amplitude / frequency" curve. The gain of the entire active filter FAD is however adjusted by adjusting the gain of the input stage 2 to 6, also by varying the values of its resistive components. The gain value of the active filter FAD s is for example chosen to be 1. It is particularly advantageous that the settings of the resistive components of each stage of the active filter FAD according to the present invention are independent of the settings of the resistive components of its other stages , because this allows faster adjustment of said FAD filter, avoiding that the adjustments of one stage do not disturb those, previously made, of another stage.

As indicated above, the operational amplifiers 7a to 7c are also chosen of a type with low electrical consumption, this electrical consumption can be adjusted to the minimum value, compatible with correct operation of each SALLEN structure. KEY, by adjusting the value of a resistance 6a, 6b or 6c.

Means are associated with the operational amplifier 7a of the input structure 7a to 14a, of the active filter FAD, for adjusting; o the offset voltage of said operational amplifier 7a so as to obtain a very low DC voltage on the line of output 15 of said active FAD filter; in the embodiment illustrated in FIG. 1, these means are materialized by two resistors, 16a and 16b, which are connected to inputs 25

appropriate of the operational amplifier 7a, and whose values are adjusted, for example in the known manner, previously indicated, so as to minimize the offset voltage of said operational amplifier 7a. We thus achieve that, at rest, that is to say in the absence of a signal on the input terminal m 47 of the active filter FAD, its output line 15 delivers a very low current in the impedance connected to it.

The exit line! 5 of the active demodulation filter FAD is connected to the input terminal 9 of the electronic switch AG 35 (FIG. 2), the other input terminal of which, 9 ′, is connected to ground. The telephone line, not shown, is connected to two other terminals, 7 and 7 ′, of the electronic switcher AG, the second T of which is also connected to ground. Between the input terminals 7 and 9 of the electronic switcher, that is to say between the telephone line 4II and the demodulation channel, is inserted an adaptation resistor 17, whose role is to ensuring the impedance matching between said telephone line and said demodulation channel.

The electronic switch AG additionally comprises an operational amplifier 18, which can be of the same type as the operational amplifiers 2 and 7a to 7c (FIG. 1). It includes in particular a resistor, 6d, for adjusting its electrical consumption. The output of the operational amplifier 18 is connected to the first of the two output terminals, 8 and 8 ', of 50

the AG electronic switch; to the first, 8, of these two output terminals is connected the demodulation channel, which will be described later, while the second terminal, 8c. is connected to ground. Between the first positive input of the operational amplifier 18 and the input terminal 9 of the electronic switch 55 AG, which is connected to the output line 15 of the active demodulation filter FAD, is inserted into a compensation network. line impedance variations; in the embodiment illustrated in FIG. 2, this compensation network comprises two cells of the RC type, connected in series, which Ml can be adjusted separately to act one at low telephone frequencies, and the other at high telephone frequencies ; in particular, each of the two cells is constituted by a branch in series, formed by a resistor, 19a or 19b, in parallel on a capacitor, 20a or 20b, this branch h5 in series being followed by a resistor in parallel, 21a or 21b . The values of the various components 19a to 21a and 19b to 21b of the compensation network are chosen so that the latter behaves, as a function of the frequency, so that the dipole connected to the input terminals 7 and 7 ′, c that is, the telephone line; the impedance of the latter varying between wide limits, not only as a function of the frequency of the telephone signals, but also according to the state of the line, and in particular the position of the station to which it terminates, the compensation network which comes to be described makes it possible to attenuate to a large extent the influence of these variations in line impedance on the signals that the electronic signal controller AG transmits to the modulation channel.

As for the second, negative, input of the operational amplifier 18, it is connected to an intermediate point, 22. of a voltage divider, constituted by two resistors, 23a and 23b, connected in series, one with the other, and inserted between the input terminal 7 of the electronic switch AG which is connected to the telephone line, and the output of the operational amplifier 18. The ratio of the values of the resistors 23a and 23b is chosen in such a way that a signal arriving at the input terminal 9 of the electronic signal controller AG, coming from the demodulation channel, and transmitted through the adaptation resistor 17 to the terminal 7, itself connected to the telephone line, only produces a practically zero voltage at the output of the operational amplifier 18, so that said electronic switchman AG then hardly transmits a signal to the modulation channel connected to its output terminals et and 8 ′. A telephone signal, transmitted to terminals 7, 7 ′ by the telephone line, is on the other hand retransmitted, via the adaptation resistor 17, the compensation network, 19a to 21b, and the operational amplifier 18, at the output terminals 8, 8 'of the electronic signal controller AG, and consequently as a result of the modulation channel, possibly with a determined gain; on the other hand, the same telephone signal arriving at the input terminals 7, 7 'of the electronic switch AG cannot be transmitted to the d-modulation channel via the active filter FAD (FIG. 1), from the causes line 15 to transmit said telephone signal to the output of operational amplifier 7c.

For the telephone signal arriving by the line, the electronic switch AG behaves like an amplifier, the gain of which can be adjusted by adjusting the values of the various resistive components, in particular of the two resistors 23 a and 23 b; it is preferably chosen to give a gain of value 1 to the electronic switch AG. One of the advantages of the device according to the invention lies in the independence of the adjustable components which are respectively part of the modulation channel and of the demodulation channel, which makes it possible to adjust these two channels one independently of the other.

The input of the active modulation FAM filter, shown diagrammatically on the left-hand side of FIG. 2, is coupled to the corresponding output, 8, of the electronic switch AG, by a capacitor 24, mounted in series, the purpose of which is avoid the transmission, to the active modulation FAM filter, of a direct voltage, likely to disturb the operation of the omnibus modulation line, OM, itself connected to the output terminal 30 of said active FAM filter (see also Figure 9 of the main patent).

Although the device according to the present invention may include an active demodulation filter of any suitable type, the embodiment of the active modulation filter, FAM, which is visible on the left side of Figure 2 corresponds to that which is described in the French patent application for "Active filter, with independently adjustable parameters", which the Applicant filed on November 14, 1975 under No. 75 34823. The essential component of this active modulation filter, FAM, is still an operational amplifier with low power consumption, 25, which can be of the same type as the operational amplifiers 2, 7a to 7c and 18, previously mentioned; like them, it has a 6th resistor,

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whose value is adjusted, for example by the known methoke, previously indicated, so as to adjust the electrical consumption of the operational amplifier 25 to the minimum value, compatible with correct operation of the active modulation filter, FAM. The operational amplifier 25 is also associated with two resistors, 16c and 16d, which make it possible to adjust its offset voltage so as to obtain a very low DC voltage on the output 30 of the active filter FAM, for the reasons mentioned above. The gain of the active modulation filter, FAM, is adjusted, as described in the French patent application mentioned above, preferably to the value 2.

A capacitor 26 is mounted in parallel between the ground, on the one hand, and, on the other hand, the output terminal 30 of the active filter FAM. This capacitor 26 acts as a reservoir of electrical energy, for peaks of current intensity, linked to the operation of the sampling gate which can be inserted between the output terminal 30 of the active filter FAM and the bus line of OM modulation, as illustrated for example in FIG. 9 of the main patent. This provision is made necessary by the fact that the measures taken to limit the electrical consumption of the operational amplifier 25 of the active filter FAM, are such as to prevent it from supplying the peaks of current intensity, which have been mentioned.

The device illustrated in Figures 1 and 2, although designed to be reccordé a two-wire telephone line, can be easily adapted for connection to a four-wire telephone line; for this, it is sufficient to cut the 5 output connections of the electronic switch AG at the arrows F1 and F2; the two “incoming” wires of the telephone line are then connected to the terminals, 7, 7 ′, of the electronic switcher, so that they receive the signals transmitted by the active demodulation filter, FAD, without amplification, io since said active filter FAD has an overall gain of value 1; the “outgoing” wires of the telephone line are on the other hand connected, via an attenuator and a coupling transformer, to terminals 27, 27 ′, the second of which is connected to ground, while the first is connected to the i5 modulation channel, via the output terminal 8 of the electronic switch AG and the capacitor 24; the attenuator mentioned is preferably adjusted so as to compensate for the gain, of value 2, of the active modulation filter, FAM.

As already mentioned, the values of all the 2i) resistive components of the various circuits of the device according to the present invention can be adjusted for example by using a beam of laser radiation, controlled by an automatic device, so as to compensate for the tolerances on the values of the capacitive components and of the parameters of the amplifiers that these circuits comprise.

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2 sheets of drawings