GB1562916A - Apparatus for transmitting and receiving pulses - Google Patents

Description

(54) APPARATUS FOR TRANSMITTING AND RECEIVING PULSES (71) We, ASSOCIATION DES OUVRIERS EN INSTRUMENTS DE PRE CISION, a French body corporate of 8-14 rue Chaires Fourier, Paris, France, 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: This is an addition to our patent No.

1,424,381, which relates to an apparatus for transmitting and receiving coded telephone pulses, including a modulation channel and a demodulation channel, each comprising a telephone signal amplifier, a low pass filter, and means for pulse modulating or demodulating telephone signals respectively and being connectable to a subscriber's telephone line through a hybrid converter which consists of at least one semiconductor active circuit having at least a first pole connected to the subscriber's line, a second pole connected to the modulation channel, and a third pole connected to the demodulation channel.

In accordance with another feature of the apparatus described in the main patent, the modulation and demodulation channels may each include an active filter which performs the function of filter and amplifier either for modulation or demodulation.

The present invention relates to various modified embodiments of the active filters for modulation and demodulation and of the hybrid converter, which are provided in the apparatus described in our said patent No. 1,424,381.

In the said patent there is described an embodiment of the active demodulating filter which was of the so-called Sallen Key type and which exhibited Tschebyschev behaviour.

From a first aspect the present invention consists in apparatus comprising an active modulating filter, and an active demodulating filter of the Sallen Key type of the sixth order, each of said active filters comprising at least one operational amplifier, and wherein the active demodulating filter has a response curve of the low-pass type adapted to compensate for the 1uT (sin-)/- 2 2 distortion which is due to the demodulation ( being the angular frequency of the low frequency signal and r the duration of each sampling signal).

In a preferred embodiment, the active demodulating filter may comprise apparatus wherein the active demodulating filter comprises three second order active structures of the Sallen Key type, which are connected in series, said second order active structures being adapted so that the output structure has a Q factor higher than that of the input structure and lower than that of the mid structure. Preferably, the input structure is preceded by an operational amplifier which is connected as an active attenuator and whose gain is adjusted according to the gains of the amplifiers in the three Sallen Key structures.

From a second aspect the invention consists in apparatus either as claimed in claim 1 of patent No. 1,424,381 or as set forth above, wherein the hybrid converter comprises a matching resistor which is inserted between the demodulation channel and the subscriber's line, and an operational amplifier which has an output connected to the modulating channel, a first input connected to the demodulating channel via a network for compensating for impedance variations in the subscriber's line, and a second input connected to an intermediate point in a voltage divider inserted between the line and the output of the said operational amplifier, the said intermediate point in the voltage divider being so selected that a signal arriving from the demodulation channel produces virtually no voltage at the output of the operational amplifier.In this way, the signal arriving from the demodulation channel is transmitted through the matching resistor to the subscriber's line with a suitable impedance while the output of the operational amplifier transmits scarcely any signal to the modulating channel. One the other hand, the operational amplifier of the hybrid con verter transmits a signal arriving from the line to the modulation channel with a predetermined gain while correcting frequency to enable variations in the electrical characteristics of the subscriber's line to be compensated for.

In a preferred embodiment the compensating network may comprise a first and a second circuit of the RC type, connected in series, which are separately adjusted so that the said first and second RC circuits compensate for line impedance variations at low telephonic frequencies and at high telephonic frequencies respectively. Preferably, each circuit is formed by a series branch consisting of a resistance and a capacity in parallel, followed by a resistance in parallel.

Various means were also described in patent No. 1,424,381 for reducing the electrical power consumption of the apparatus for transmitting and receiving coded telephone pulses, and in particular for limiting the electrical consumption of its various circuits when they were not operating.Thus a preferred embodiment of the present invention may comprise various arrangements which enable the consumption of each of the various circuits of the apparatus to be reduced while at the same time adjusting the said consumption to a value, suitable to allow the corresponding circuit to operate under optimum conditions, this last object being further achieved while stilI allow ing for the said various circuits, and in par ticular the said operational amplifiers, to be formed by standard integrated circuits, prefer ably of the same type with low consumption.

For this purpose in accordance with a feature of the present invention, there may be used operational amplifiers whose electrical con sumption can be adjusted, in particular by means of resistors of suitably adjustable values.

The same standard type of operational amplifier may thus be used for example both in the hybrid converter and in the active modulating and demodulating filters of the apparatus according to the present invention, the consumption of each operational amplifier being set to the minimum level compatible with the satisfactory operation of the related circuit by suitably adjusting the values of the said resistors.

The electrical consumption of each of the active modulating and demodulating filters of the apparatus according to the present invention, particularly in the quiescent state, may also be reduced by associating means, such as resistors of suitably adjusted values, with at least one of the operational amplifiers of the said active filters to adjust the offset voltage of the said operational amplifier so as to obtain a very low DC voltage on the output of the corresponding active filter. The result is obviously a very low consumption of DC electrical energy in the impedance which is connected to the output of the said active filter.

In order that the present invention may be more readily understood an embodiment of apparatus according to the present invention is described below and illustrated schematically in the accompanying drawings, in which Fig. 1 is a circuit diagram of an embodiment of active demodulating filter according to the present invention.

Fig. 2 is a circuit diagram of an embodiment of electronic switch and an embodiment of active demodulating filter according to the present invention.

In Fig. 1, the same reference numeral 47 is used as in Fig. 9 of our patent No. 1,424,381 to refer to the input terminal of the active demodulating filter FAD of an apparatus constructed in accordance with the invention.

This input terminal 47 of the active demodulating filter FAD is connected, via a coupling capaciter 1 connected in series to an omnibus demodulation line OD and to one of the terminals of a storage capacitor 102 whose other terminal is connected to earth and which acts as an integrating capacitor for pulse demodulations. In other words, the cyclic amplitudemodulated pulses which are transmitted along the omnibus demodulation line OD are stored in the storage capacitor 102, whose charge voltage thus varies in the course of time in a staircase curve while its AC component is transmitted bathe coupling capacitor 1 to the input terminal 47 of active filter FAD.

The embodiment of the active demodulating filter FAD which is shown diagrammatically in Fig. 1 has an input stage which is formed basically by an operational amplifier 2 of low electrical consumption which is preferably of a standard type such as the type known by the serial number 776. The operational amplifier 2 is connected as an active attenuator. Its negative input is connected to the input terminal 47 of filter FAD via a resistor 3 of suitable value, while its positive input is connected to earth via a resistor 4.

Because of the coupling capacitor 1, no DC voltage which might possibly be transmitted from the omnibus demodulating line OD is able to upset the operation of operational amplifier 2. A feedback resistor 5 is connected between the output of operational amplifier 2 and its negative input. In addition, the operational amplifier 2 is selected to be of a tvne whose electrical consumption can be adjusted, in particular by means of a resistor 6 whose value is adjusted to allow the said operational amplifier 2 to have the minimum consumption compatible with the input stage of active filter FAD operating under satis- factory conditions. The operational amplifier 2 and the resistors 3 to 6 preferably form a solid-state integrated circuit in which the resistors may for example take the known form of resistive tracks. The value of resistor 6 may in particular be adjusted, for the purpose mentioned above, by suitably altering at least one of its transverse dimensions, using for example the action of a beam of laser radiation which is controlled by an automatic apparatus.

The next three stages of the active filter FAD, which are connected in series with each other and with the operational input amplifier 2, each contain an operational amplifier, 7a, 7b, or 7c, which may be of the same type as operational amplifier 2. Each stage also includes 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 appropriate operational amplifier, such as 7a, and to its output in such a way as to form with the amplifier a second order structure of the socalled Sallen Key type, whose Q factor is determined by the values selected for the various components 8a to 14a. The three Sallen Key structures, which are connected in series, have their components so selected that the output structure 7c to 14c has Q factor which is higher than that of the mid structure 7b to 14b.Since each of the three Sallen Key structures is of the second order, when connected in series they form an active filter of the sixth order, which has a response curve of the low-pass type and compensates for the (sin-)/- 2 2 distortion which is due to the demodulation ( being the angular frequency of the low fre quency signal and r being the duration of the sampling signal). By virtue of these charac teristics of the active demodulating filter FAD just described, the filtered and amplified signal which appears on the output line 15 from the active filter FAD shows very little distortion.

The active filter formed by the three Sallen Key structures described above has an "amplitude/frequency" curve which can be adjusted by varying, for example in the way indicated above, the values of at least some of the resistive components of the three structures in order to compensate for possible deviations from their specified values on the part of the capacitive components such as 13a and 14a, and on the part of the parameters of the operational amplifiers such as 7a, and thus to obtain the desired "amplitude/frequency" curve. The overall gain of the active filter FAD on the other hand is adjusted by regulating the gain of the input stage 2 to 6, which is also done by varying the values of its resistive components. The gain of the active filter FAD is for example selected to be equal to 1.It is particularly advantageous for the adjustment made to the resistive components in each stage of the active filter FAD to be independent of the adjustments made to the resistive components in its other stages, since this allows the said filter FAD to be adjusted more quickly while preventing adjustments made to one stage from upsetting those made previously to another stage.

As indicated above, the operational amplifiers 7a to 7c are also selected to be of a type having low electrical consumption, which electrical consumption may be adjusted to the minimum value compatible with each Sallen Key structure operating properly by adjusting the value of a resistor 6a, 6b or 6c.

Also associated with the operational amplifier 7a in the input structure 7a to 14a of the active filter FAD are means operative to adjust the offset voltage of the said operational amplifier 7a so as to obtain a very low DC voltage on the output line 15 from the said active filter FAD. In the embodiment shown in Fig. 1, these means take the form of two resistors 16a and 16b which are connected to appropriate inputs of the operational amplifier 7a and whose values are adjusted, for example in the known way mentioned above, so as to minimize the offset voltage of the said operational amplifier 7a. By this means it is possible to ensure that in the quiescent state, that is to say when there is no signal at input terminal 47 of the active filter FAD, the output line 15 of the filter feeds a very low current into the impedance which is connected to it.

The output line 15 of the active demodulating filter FAD is connected to the input terminal 9 of a hybrid converter AG (Fig. 2), whose input terminal 9' is connected to earth.

The telephone subscriber's line, which is not shown, is connected to two other terminals 7 and 7' of the electronic switch AG, the second of which, 7' is likewise connected to earth. Between the input terminals 7 and 9 of the hybrid converter AG that is to say between the sub srriber's line and the demodulation channel, is placed a matching resistor 17 the purpose of which is to match impedance between the said subscriber's line and the said demodulation channel.

The hybrid converter AG also includes an operational amplifier 18 which may be of the same type as the operational amplifiers 2 and 7a to 7c (Fig. 1). The amplifier 18 has in particular a resistor 6d for adjusting its electrical consumption. The output of operational amplifier 18 is connected to the first of the two output terminals, 8 and 8', of the hybrid converter AG. To the first, 8, of the two output terminals is connected the modulation channel which will be described below, while the second terminal, 8', is connected to earth. Between the first, positive input of the operational amplifier 18 and the input terminal 9 of the hybrid converter AG, which is connected to the output line 15 of the active demodulating filter FAD, is inserted a network for compensating for impedance variations in the subscriber's line. In the embodiment shown in Fig.

2, this compensating network consists of two circuits of the RC type connected in series which can be separately adjusted so as to separately compensate for line impedance variations at low telephonic frequencies and at high telephonic frequencies, respectively. In particular, each of the two RC circuits has a series branch formed by a registor 19a or 19b in parallel with a capacitor 20a or 20b, this series branch being followed by a parallel resistor 21a or 21b. The values of the various components 19a to 21a and 19b to 21b in the compensating network are so selected that the latter has the same frequency response curve as the dipole connected to the input terminals 7 and 7', i.e. the telephone line.Since the impedance of the latter varies within wide limits not only as a function of the frequency of the telephone signals but also as a function of the state of the subscriber's line and in particular of the position of the subscriber's set to which it is connected, the compensating network which has just been described efficiently attenuates the effect of the line impedance variations on the signals to be transmitted to the modulation channel through the hybrid converter AG.

The second, negative input of operational amplifier 18 is connected to an intermediate point 22 in a voltage divider which is formed by two resistors 23a and 23b connected in series with one another and inserted between the input terminal 7 of the hybrid converter AG which is connected to the telephone subscriber's line and the output of operational amplifier 18. The ratio of resistors 23a and 23b is so selected that a signal arriving at the input terminal 9 of the hybrid converter AG from the demodulation channel which is transmitted to subscriber's line through matching resistor 17 and terminal 7, produces virtually no voltage at the output of operational amplifier 18, so that the said hybrid converter AG thus transmits virtually no signal to the modulation channel which is connected to its output terminals 8 and 8'.Conversely, a telephone signal which is transmitted to terminals 7 and 7' from the subscriber's line is retransmitted, via rnatching resistor 17, via the compensating network 19a to 21b and via operational amplifier 18, to the output terminals 8, 8' of the hybrid converter AG and thus to the modulation channel with, possibly, a predetermined gain. On the other hand, the same telephone signal arriving at the input terminals 7, 7' of the hybrid converter AG cannot be transmitted through matching resistor 17 and terminal 9 to the demodulation channel comprising the active filter FAD (Fig. 1), owing to the fact that line 15 transmits the said telephone signal to the output of operational amplifier 7c.

For the telephone signal which arrives from the subscriber's line, the hybrid converter AG operates as an amplifier, whose gain can be adjusted by adjusting the values of the various resistive components and in particular that of the two resistors 23a and 23b. A value of 1 is preferably selected for the gain of the hybrid converter AG. One of the advantages of the apparatus described lies in the independence of the adjustable components which form part of the modulation channel and the demodulation channel respectively, which enables the two channels to be adjusted independently of one another.

The input of the active modulating filter FAM, which is shown schematically in the left-hand part of Fig. 2, is coupled to the output 8 of hybrid converter AG by a series capacitor 24, the purpose of which is to prevent transmission to the active modulating filter FAM of a DC voltage liable to upset the operation of the omnibus modulation line OM which is connected to the output terminal 30 of the said active filter FAM (see also Fig. 12 of the main patent).

Although the apparatus according to this invention may comprise any suitable type of active modulating filter, the active modulating filter FAM which is shown in the left-hand part of Fig. 2 corresponds to that described in our France patent specification No.

75. 34823. The chief component of this active modulating filter FAM also is an operational amplifier having low electrical consumption, which may be of the same type as the operational amplifiers 2, 7a to 7c and 18 mentioned above. Like them, it has a resistor 6e whose value is adjusted, for example by the known method mentioned above, in such a way as to adjust the electrical consumption of the operational amplifier 25 to the minimum level compatible with the active modulating filter FAM operating properly. Also associated with operational amplifier 25 are two resistors 16c and 16d which enable its offset voltage to be adjusted in such a way as to obtain a very low DC voltage at the output 30 of the active filter FAM, for the reasons mentioned above.

The gain of the active modulating filter FAM is adjusted, in the manner described in our French patent application mentioned above, to a preferred value of 2.

A capacitor 26 is connected in parallel between earth on the one hand and the output terminal 30 of active filter FAM on the other.

This capacitor 26 performs the function of an electrical energy store for the current peaks which the operation of the sampling gate involves, which gate may be inserted between the output terminal 30 of the active filter FAM and the omnibus modulation line OM, as illustrated in Fig. 12 of the main patent for example. This arrangement is made necessary by the fact that the steps taken to limit the electrical consumption of the operational amplifier 25 in the active filter FAM are such as to prevent it from supplying the current peaks mentioned.

The apparatus shown in Figs. 1 and 2, although designed with a view to being con nected to a two-wire telephone subscriberzs line, may easily be adapted for the purpose of connection to a four-wire telephone line. For this, it is merely necessary to cut the output connections of hybrid converter AG where indicated by arrows F1 and F2. The two "incoming" wires of the telephone line are then connected to terminals 7, 7' of the hybrid converter, so that they will receive signals transmitted by the active demodulating filter FAD without amplification, since the overall gain of the active filter FAD is 1.The "outgoing" wires of the telephone line on the other hand are, connected, via an attentuator and a coupling transformer, to terminals 27, 27', of which the second is connected to earth while the first is connected to the modulation channel via the output terminal 8 of hybrid converter AG and capacitor 24. The attenuator mentioned is so adjusted as preferably to compensate for the gain, of value 2, of the active modulating filter FAM.

As already mentioned, the values of all the resistive components of the various circuits in the apparatus according to the present invention may for example be adjusted by using a beam of laser radiation under the control of an automatic device so as to compensate for the tolerances on the values of the capacitive components and on the parameters of the amplifiers which the said circuits comprise.

WHAT WE CLAIM IS: 1. Apparatus according to claim 11 of patent No. 1,424,381, comprising an active modulating filter, and an active demodulating filter of the Sallen Key type of the sixth order, each of said active filters comprising at least one operational amplifier, and wherein the active demodulating filter has a response curve of the low-pass type adapted to compensate for the t > T WT (sin )/~ 22 distortion which is due to the demodulation (w being the angular frequency of the low frequency signal and 7 the duration of each sampling signal).

2. Apparatus according to claim 1, wherein the active demodulating filter comprises three second order active structures of the Sallen Key type, which are connected in series, said second order active structures being adapted so that the output structure has a Q factor higher than that of the input structure and lower than that of the mid structure.

3. Apparatus according to claim 2, wherein the input structur preceded by an operational amplifier which is connected as an active attenuator and whose gain is adjusted according to the gains of the amplifiers in the three Sallen Key active structures.

4. Apparatus according to any one of claims 1 to 3, wherein the output of the demodulator is coupled to the input of the active demodulating filter through a series capacitor.

5. Apparatus according to either claim 1 of patent No. 1,424,381, or claims 1 to 4 of the present application, wherein the hybrid converter comprises a matching resistor which is inserted between the demodulation channel and the subscriber's line, and an operational amplifier which has an output connected to the modulating channel, a first input connected to the demodulating channel via a network for compensating for impedance variations in the subscriber's line, and a second input connected to an intermediate point in a voltage divider inserted between the line and the output c:: the said operational amplifier, the said intern mediate point in the voltage divider being selected that a signal arriving frown the at modulation channel produces virtuallv voltage at the output of the operational amnb lifier.

6. Apparatus according to claim 5, wherein the compensating network comprises a first and a second circuit of the RC te c cnnec- series, which are adjusted saparatel-r so the the said first and second RC rircr?ts pensate for line impedance variation aL telephonic frequencies and at high telephonic frequencies, respectively 7. Apparatus according to claim 4 Tv}le each circuit is formed by a series branch zc sisting of a resistance and a capacitance m parallel, followed bv a resistance in parallel 8. Apparatus according to any one of claims 1 to 7, wherein each of said operational amplifiers has means for adjusting its electrical con sumption.

9. Apparatus according to either one claims 11 and 12 of the patent No. 1,424,381, and claims 1 to 7 of the present application wherein resistor means are associated wits least one of the operational amplifiers of Jie active modulating and demodulating filters to adjust the offset voltage of the said one operational amplifier in such a way as to obtain a negligible DC voltage on the output of the active filter comprising the said one operational amplifier.

10. Apparatus for transmitting and receiving coded telephone pulses substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. nected to a two-wire telephone subscriberzs line, may easily be adapted for the purpose of connection to a four-wire telephone line. For this, it is merely necessary to cut the output connections of hybrid converter AG where indicated by arrows F1 and F2. The two "incoming" wires of the telephone line are then connected to terminals 7, 7' of the hybrid converter, so that they will receive signals transmitted by the active demodulating filter FAD without amplification, since the overall gain of the active filter FAD is 1.The "outgoing" wires of the telephone line on the other hand are, connected, via an attentuator and a coupling transformer, to terminals 27, 27', of which the second is connected to earth while the first is connected to the modulation channel via the output terminal 8 of hybrid converter AG and capacitor 24. The attenuator mentioned is so adjusted as preferably to compensate for the gain, of value 2, of the active modulating filter FAM. As already mentioned, the values of all the resistive components of the various circuits in the apparatus according to the present invention may for example be adjusted by using a beam of laser radiation under the control of an automatic device so as to compensate for the tolerances on the values of the capacitive components and on the parameters of the amplifiers which the said circuits comprise. WHAT WE CLAIM IS:

1. Apparatus according to claim 11 of patent No. 1,424,381, comprising an active modulating filter, and an active demodulating filter of the Sallen Key type of the sixth order, each of said active filters comprising at least one operational amplifier, and wherein the active demodulating filter has a response curve of the low-pass type adapted to compensate for the t > T WT (sin )/~ 22 distortion which is due to the demodulation (w being the angular frequency of the low frequency signal and 7 the duration of each sampling signal).

2. Apparatus according to claim 1, wherein the active demodulating filter comprises three second order active structures of the Sallen Key type, which are connected in series, said second order active structures being adapted so that the output structure has a Q factor higher than that of the input structure and lower than that of the mid structure.

3. Apparatus according to claim 2, wherein the input structur preceded by an operational amplifier which is connected as an active attenuator and whose gain is adjusted according to the gains of the amplifiers in the three Sallen Key active structures.

4. Apparatus according to any one of claims 1 to 3, wherein the output of the demodulator is coupled to the input of the active demodulating filter through a series capacitor.

5. Apparatus according to either claim 1 of patent No. 1,424,381, or claims 1 to 4 of the present application, wherein the hybrid converter comprises a matching resistor which is inserted between the demodulation channel and the subscriber's line, and an operational amplifier which has an output connected to the modulating channel, a first input connected to the demodulating channel via a network for compensating for impedance variations in the subscriber's line, and a second input connected to an intermediate point in a voltage divider inserted between the line and the output c:: the said operational amplifier, the said intern mediate point in the voltage divider being selected that a signal arriving frown the at modulation channel produces virtuallv voltage at the output of the operational amnb lifier.

6. Apparatus according to claim 5, wherein the compensating network comprises a first and a second circuit of the RC te c cnnec- series, which are adjusted saparatel-r so the the said first and second RC rircr?ts pensate for line impedance variation aL telephonic frequencies and at high telephonic frequencies, respectively

7. Apparatus according to claim 4 Tv}le each circuit is formed by a series branch zc sisting of a resistance and a capacitance m parallel, followed bv a resistance in parallel

8.Apparatus according to any one of claims 1 to 7, wherein each of said operational amplifiers has means for adjusting its electrical con sumption.

9. Apparatus according to either one claims 11 and 12 of the patent No. 1,424,381, and claims 1 to 7 of the present application wherein resistor means are associated wits least one of the operational amplifiers of Jie active modulating and demodulating filters to adjust the offset voltage of the said one operational amplifier in such a way as to obtain a negligible DC voltage on the output of the active filter comprising the said one operational amplifier.

10. Apparatus for transmitting and receiving coded telephone pulses substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

11. Apparatus for transmitting and receiv

ing coded telephone pulses substantially as hereinbefore described with reference to Figure 2 of the accompanying drawing.