Commutation grid

A commutation grid in which any of N input signals can be output to any of M outputs. The input signals are fed to an input card which passes the input signals to an output card via a commutation card. These card elements are supported in a rack system which allows each card to make an appropriate contact with any other card. A user is also permitted to issue a command order which controls the operation of the communication card.

The present invention relates to a commutation grid intended for the 
distribution at will of a signal on M outputs, notably a video signal, 
selected amongst N signals applied to as many inputs on the grid, whereby 
each of the M outputs can be commuted at will with any one of the N inputs 
as a function of an appropriate telecontrol signal. 
It is known that the distribution systems or networks of video signals are 
considerably developing at present, by using cables or optic fibers, such 
as those disclosed in EP-A-0 118 161 or FR-A-2 285 758, which allow 
providing to a group of distinct users the images of multiple programs 
arising from simultaneous or preregistered transmissions distributed on 
the network. These images are intended to be received according to a 
choice of some sort by the users, who can at will select those images 
which they wish to receive on their receiving apparatus, which can be a TV 
set, a tape recorder, a monitor or other device, according to each 
individual case. Likewise, for the distributor of these images, it may be 
necessary to control and/or check their transfer for, for example, levying 
a right or toll on some programs, controlling the duration of reception of 
the transmission in view of an automatic charge or invoicing, putting in 
service or stopping these programs from a centralized control... More 
generally, it may also be advantageous to have a system which is partly 
interactive, allowing in a certain measure a possible conversation or 
dialogue between the users for, for example, carrying out public opinion 
polls, measuring the audience rating, directing product buys or orders 
through the television set, etc... 
Likewise, it is conceivable that such distribution networks with a 
commutation grid of the hereabove type present a particular interest in 
the field of collectivities equipment such as for groups of buildings, 
hotels, hospitals..., where it is thus possible for each user to receive 
the images chosen amongst a large number of programs, with a considerable 
diversity, by receiving of course not only these images, but also the 
sound, in monophony as well as in stereophony, and even only the sound 
incoming from other sources and purely auditive (especially broadcast 
programs). 
According to EP-A-0 152 173 in particular, commutation grids have already 
been considered which are in the form of a matrix with interconnected 
lines and columns, allow establishing at will a connection between N 
inputs and M outputs of the matrix, thereby providing the transmission of 
any selected signal to a user, also predetermined. However the units 
presently available are generally very complex, costly and have a 
relatively complicated usage, their use and above all their installation 
in optimal efficiency conditions being difficult. Moreover, in the 
commutation systems disclosed in the hereabove patent, the commutation 
cards used receive only a single input signal, which is a high frequency 
signal. 
On the other hand, there is known from patent application Ser. No PCT/FR 
88/00046, corresponding to U.S. Pat. No. 07/243,029, which is incorporated 
herein by reference a method and a device for a simple and reliable 
transmission, particularly without degradation of the signal, of a video 
signal or other signal, incoming from any source (television set, tape 
recorder, camera, receiver of TV transmissions or by satellite, even a 
computer monitor, etc...) and applied to a receiver situated at a 
distance, via a twin-line lead made of two wires of a very small section, 
practically less than a millimiter and, consequently, which are very 
discrete, flexible, easy to lay and to conceal along its path without 
necessitating installation works of the type of those necessary if the 
video signal has to be transmitted by a coaxial cable. Thus, due to this 
method and from any source situated at a distance (which distance can 
reach 300 meters or more), any type of video signal can be transmitted in 
any stantard (, SECAM, D2 MAC PAQUET ...), to an appropriate receiving 
set, the system being designed in such a manner that the controls of the 
source (ON, OFF, possibly a review motion, a still-frame pause, recording, 
setting of the sound, light or contrast levels,...) can be telecontrolled 
from the receiving set by the user himself, who uses, in reverse 
direction, the same twin-line lead which transmits the video signals for 
conveying the necessary telecontrol signals. 
The object of the present invention is a commutation grid which meets the 
aforementioned requirements, notably by putting in practice the hereabove 
method for the transmission of the delivered signal, by allowing 
transmission on any output line, chosen amongst a given number of such 
lines, a video signal selected from a group of different signals arriving 
from a common network, which is simple, inexpensive, reliable and which 
can provide upon request and according to the user's wish the commutations 
he desires. 
The commutation grid according to the present invention is, on the other 
hand, designed in such a manner as to avoid crosstalk between the video 
signals flowing through the connections of the grid, the signals being 
transmitted without distortion or attenuation in a frequency band which 
can range from a few tens of Hz to 30 MHz or more, the grid being finally 
on a compact and modulable structure, without limitation of the N number 
of inputs receiving the signals to be transmitted to the M number of 
outputs allocated to the users, and each receiving at will any one of the 
input signals. 
According to the present invention, the commutation grid in consideration 
is characterized in that it includes a fixed support structure for an 
assembly of input cards each receiving signals, notably video signals, 
possibly video and/or audio signals, the number of which cards corresponds 
to a given sub-multiple of the total number of N signals to be 
transmitted; 
- at least a sub-assembly of commutation cards, each of which is connected 
to an input card; 
- and at least one sub-assembly of output cards, all connected to the 
assembly of commutation cards and each delivering to a user any signal 
selected amongst the received signals by each commutation card from the 
associated input card, the commutation cards including an assembly of 
input cells mounted in parallel, the number of which is equal to that of 
the sub-multiple defining the number of video signals to be transmitted 
and received by an input card and an assembly of output cells, their 
number being equal to that of the output cards, each input cell and each 
output cell being joined by a commutation cell, which lets pass a selected 
signal from the input to the output under the effect of a command order 
given by the user, flowing through the output card associated to said 
user, via a treatment card which is common to the assembly of commutation 
cards, said treatment card controlling a conversion stage of the received 
orders, the support structure including at least one rack containing a 
sub-assembly of parallel commutation cards and a sub-assembly of output 
cards, also parallel but disposed perpendicularly to the commutation 
cards, the contact point of the edges or ridges of each commutation card 
with the associated edge of the corresponding output card providing the 
connection between an output cell on the commutation card and a selection 
circuit provided on the output card thus united. 
According to a particular feature of the present invention, the treatment 
card is parallel to the commutation cards and is in contact via an edge 
with the output cards. 
Preferably, the selection circuit output is connected to a transmitting 
circuit for restoring on two distinct conductors the respective audio and 
video signals prior to the transmission of the latter on a twin-line lead 
conveying them to a remote appropriate receiver. Notably, the present 
commutation grid according to the invention advantageously puts in 
practice, as regards the transmitter, the receiver and the twin-line lead 
connecting them, the dispositions of the aforementioned patent application 
U.S. 07/243,029. 
Also according to another feature of the present invention, each 
commutation card of a sub-assembly is joined to the output of an input 
card by an adapted coaxial cable each, the cables conveying a signal 
received by the input card toward each of the commutation cards of the 
corresponding sub-assembly, the adaptation of the cable being provided at 
its ends by the input cards and a terminal resistor, respectively.

FIG. 1 shows schematically the relative mounting in a fixed support 
structure of the various input, commutation, output and treatment cards, 
which are part of the commutation grid according to the present invention. 
Thus, the system includes a first assembly of cards such as 1, 1a... 1n, 
called input cards, for video V and audio A signals for example, delivered 
to the inputs of the input cards 1 and incoming from an assembly of 
coaxial cables or from a beam of standard optic fibers (not shown). These 
respective audio and video signals are previsously treated, if necessary, 
in appropriate demodulation and adaptation stages (also not shown but well 
known in the technique), the video and audio signals are thus provided in 
a base band. 
The signals thus applied to the input cards form therefore an assembly of n 
signals, which are distributed into distinct groups each forming a given 
sub-multiple of N, each group of signals being therefore allocated to an 
input card such as 1, 1a,...1n. It should be noted that these signals can 
be independent or more generally exploited at least two by two, 
particularly when a television image is to be transmitted, where the video 
signal is necessarily accompanied by an associated audio signal. Also, one 
can envisage that the same video signal is associated with two audio 
signals corresponding to a transmission of a stereophonic signal. On the 
contrary, one can also envisage that the input signal is only an audio 
signal, mono or stereo. The grid allows the transmission to the users of 
signals of any type, video or audio, or even others, the particular nature 
of these signals is in fact indifferent for particularly practicing the 
invention, except when there is envisaged a possible prior treatment of 
these signals in order to dispose them to an appropriate frequency band 
which is here between a few tens of a Hz and 30 MHz or more. 
Each of the outputs of each input card 1, 1a,...1n is then connected inside 
a support rack 2 of the grid to the input of a commutation card amongst a 
sub-assembly of such cards, respectively 3, 3a,...3n. As regards the input 
cards 1 as well the commutation cards 3, reference n represents notably a 
given sub-multiple of number N, corresponding to the totality of the 
signals to be treated. 
Thus and to make things clearer in a particular but non-limiting embodiment 
of the commutation grid in consideration, this grid is provided for 
treating at the input and from a network a number N of signals which is 
equal to forty-eight, each of them corresponding to a single audio signal 
or to a video signal combined with one and even with two associated audio 
signals, as hereabove indicated. The input cards 1, 1a,...1n are here 
provided for each treating each eight signals of the preceding type, which 
means that consequently the sub-multiple n corresponds in this example to 
six. In other words, six input cards 1 are available and for each 
sub-assembly six commutation cards 3, the latter being shown in FIG. 1, 
while only card 1 amongst the input cards 1 is shown in full lines, cards 
1a...1n are shown in chain-dot lines. 
The connection between any one of cards 1 and the commutation cards 3, 
3a,...3n for each of the signals to be transmitted is provided by means of 
a coaxial cable 4, conveying the signal to be treated to an input stage E 
provided on the corresponding card 3 and the details of which will made 
clear later. Each cable 4 is impedance adapted at its two ends. 
The commutation cards 3 are also connected to a sub-assembly of output 
cards 5, 5a,...5m, which collect any one of the signals treated in the 
grid and conveys it, via a twin-wire lead 6 of small section, to an 
appropriate receiver (not shown), the transmission and reception of the 
signal is carried out, at the input and the output of line 6, preferably 
according to the dispositions disclosed and claimed in the already cited 
application U.S. Pat. No. 07/243,029. Advantageously, the components 
mounted on each commutation card are placed in a zone situated in the 
prolongation of the associated output card. 
The sub-assembly constituted by the output cards 5, 5a, ...5m associated 
with the commutation cards 3 in each element of rack 2 corresponds also to 
a sub-multiple, but here to the total number M of users of the grid. 
Thereby each of these cards 5 can select independently on a twin-line lead 
6 allocated to it any input signal received by the grid and also transmit 
in the reverse direction by the same line 6 a telecontrol order causing 
the required commutation, that is the establishment of the necessary 
connection between the input line, receiving the selected signal and the 
output line corresponding to the user giving the aforementioned order. 
In the example described by way of indication, the sub-multiple m 
corresponding to the output cards 5 is chosen to equal twenty, this 
corresponding to the mounting in rack 2 of twenty cards 5, therefore 
respectively designated 5, 5a,...5m; 
However it should be noted that the commutation grid according to the 
present invention is of course not limited in its practical embodiment to 
the mounting of twenty output cards only, and that it could be provided 
with a higher number of such cards, without any particular limitation. In 
this embodiment however, rack 2 which contains the six commutation cards 3 
and the twenty output cards 5, as shown in FIG. 1, is associated with a 
second rack 2' including in turn six commutation cards 3', 3'a...3'n and 
again twenty output cards respectively 5', 5'a,...5'm, and so forth. For 
example, in order to deliver the fourty-eight input signals to sixty 
output lines and to as many users, one will adopt three successive racks 
2, 2', 2" (FIG. 2), each including twenty output cards 5 and six 
commutation cards 3. The rack assembly thus formed is in turn associated 
with six input cards 1, each of which treats eight signals delivered by 
eight coaxial cables 4, successively to each rack of the assembly. In this 
case in fact and as shown schematically in FIG. 1, but as can be seen more 
clearly in FIG. 2, the coaxial cables 4 conveying the signals from the 
input cards 1 to the cards 3, 3a,...3n of each rack are connected from one 
rack to the other by prolongators 4', 4" connecting in parallel the 
respective commutation cards, cables 4 and their respective prolongators 
4', 4" are impedance adapted at their two ends, on the one hand by the 
associated card 1 and on the other hand by an appropriate terminal 
resistor 7. 
FIG. 3 shows the diagram of the connection established between any input in 
a given input card 1, for example a video signal V associated here with an 
audio signal A, to an output card 5 and from the latter to a transmission 
line 6, via a commutation card 3. 
In card 1, the audio signal A is previously modulated by a circuit 8 while 
the video signal V, superimposed, is brought to the card in the base. The 
two signals are therefore applied to an adder circuit 9, followed by an 
adaptator stage 9a prior to their transmission via cable 4 to any one of 
cards 3. Signals A and V in consideration are, in parallel, transmitted to 
the assembly of commutation cards 3 of rack 2, or of the racks in parallel 
2', 2", by as many cables 4, respectively 4', 4". At the output of the 
commutation card 3 in consideration, the signal is transmitted to the 
output card 5 which, according to a particular feature of the grid 
according to present invention, is disposed in rack 2 (respectively 2' or 
2" according to case) in such a manner that its plane is perpendicular to 
that of the associated commutation card 3, as is shown in FIG. 1. This 
particular mounting of cards 3 and 5 allows obtaining an appreciable space 
gain in the rack, not only by associating directly to the six cards 3 of 
the example in consideration twenty cards 5, respectively parallel to each 
other in each of the corresponding sub-assemblies, but also by limiting to 
the single mutual point of contact of the edges or ridges of each of said 
cards the electrical connection necessary for the through flow of the 
signal from one card to the other. 
In FIG. 3, the point of contact 10 is represented in the form of a 
conductor for facilitating the layout, but corresponds in fact to a direct 
punctual connection from one card to the other, as is shown in FIG. 1. 
Advantageously, and as is also shown in FIG. 1, each commutation card 3 
includes on one of its faces a layout plan 11 on which are implanted 
components and connection straps 12, while the output conductors 13 and 
the corresponding weldings are constituted by the paths of a printed 
circuit extending on the other face of the card, preferably in a direction 
perpendicular to the straps 12. These dispositions allow notably reducing 
in a great measure the crosstalk effects between signals simultaneously 
received by cards 3, on the one hand, and forming a shield between the 
inputs and the outputs respectively, and on the other hand reducing ground 
current effects. In card 5, the signal received flows through a selection 
circuit 14, the details of which will be explained hereafter, followed by 
a transmitter stage 15 restoring on conductors 16 and 17 the audio A and 
video V signals, which are then collected on the twin-line lead 6 at the 
output of the card. 
According to a particular feature of the present invention and in a 
preferred embodiment which nevertheless does not present any character of 
necessity as such, other equivalent dispositions can be considered. The 
transmitting circuit 15 corresponds to the transmitting assembly described 
and shown with reference notably to FIGS. 2 and 3 of the already cited 
patent application U.S. Pat. No. 07/243,029. Notably, such a circuit is 
provided, according to this cited application which, in this respect, is 
incorporated into the present description, for establishing the 
transmission on a twin-line lead conductor of a signal, particularly a 
video signal, by feeding the line with at least one current generator 
outputting symmetrically on the wires, while being voltage-controlled by 
the signal to be transmitted, the line being adapted at each of its ends 
by an impedance equal to its characteristic impedance. More particularly 
and still with reference to the above-cited application, circuit 15 
includes two current generators disposed in series with two equal 
resistors, the median point of which is connected to the ground via a 
capacitor, the signals delivered feeding respectively line through the 
windings of symmetrical transformers, each mounted in series with one of 
the wires of the line. 
On this same twin-line lead 6 are also conveyed in the reverse direction 
and according to an additionnal characteristic of the device described in 
the above-cited application telecontrol information necessary for the 
operation of the grid, the informationd being in the form of pulses 
emitted by the user to whom is allocated an output card 5. The pulses are 
sent back in the reverse direction to that of the received signals to a 
treatment circuit 18 supplying at 19 an appropriate pulse. The pulse is 
thus conveyed to the input of a complementary card 20, called a treatment 
card, mounted in rack 2 in a separate manner to that of the commutation 
cards 3, and preferably parallel to cards 3. 
As is shown in FIG. 1, the point of contact 19 between the cards 5 and the 
treatment card 20 is provided in the same manner as point 10 for the 
commutation cards 3, by a punctual connection in contact with the 
perpendicular edges of cards, point of contact being shown in FIG. 3 in 
the form of a conductor in order to make FIG. 3 more clear. The treatment 
circuit 18 preferably also conforms to the already described disposition 
in the prior application U.S. Pat. No. 07/243,029 hereabove mentioned, and 
includes notably a differential stage, a pass-band filter and a 
demodulator followed possibly by an amplifier. The telecontrol signals 
thus treated are previously received by the twin-line lead 6 from an 
adequate source (infrared generator or other) controlling a current 
generator symmetrically operating and placed in parallel on the line with 
the receiver for the video and/or audio signals which are supplied. 
Finally, in FIG. 3 is shown schematically the treatment card 20, which 
includes notably a circuit of the microprocessor type, which decodes the 
telecontrol information received by connections 19, and applies an 
appropriate control signal to cards 3, via conductors 23. In each of cards 
3 are provided between each cable 4, applying a given signal to the card 
3, and the output point 10 with card 5, an input cell E and an output cell 
S. These two cells are connected by a commutation cell C, opened or closed 
according to the control order received from the treatment card 20 via a 
conversion stage R associated therewith. A connection 22 connects cards 20 
of the grid with an outer circuit 21, which permit the carrying out of 
complementary counting operations or the transmitting of prohibition 
signals under certain particular conditions of use. 
FIG. 4 shows a diagram of a portion of the matrix provided in the grid by 
means of the assembly of cells E and S via the commutation cells C, the 
latter being connected in lines and in columns, respectively, to the input 
and output cells in the manner thus shown. As appears in this respect from 
the above description and from the explanation already given, cells E and 
S are, respectively, eight in number, and twenty in the example more 
particularly considered where each commutation card 3 receives in fact, 
from the same input card, eight distinct signals amongst fourty-eight 
possible signals, while the sub-assembly of the six commutation cards 3, 
each receiving these eight signals, is associated with twenty output cards 
5. The diagram of FIG. 4 shows in fact only a portion of the total matrix, 
which actually includes a number of inputs which is six times greater 
(corresponding to the six input cards 1, 1a...1n) and a number of outputs 
which is three times greater (for an assumed total of sixty users) 
corresponding to the three racks in parallel 2, 2', 2". 
As regards the conversion stages R, they are arranged in the example in 
consideration so as to provide a series-parallel conversion of the 
received signals and disposed according to the columns of the portion of 
matrix which is shown, each stage interesting thus the commutation cells C 
of a column, in each commutation card 3 of the same rack. 
In the arrangement corresponding to the drawing, the mounting in parallel 
of six commutation cards and their connection at 10 with the selection 
circuit 14 of each of the output cards 5 is in fact the same as to divide 
the matrix in practice into eighteen distinct sub-assemblies (six times 
three) of which only one is shown in FIG. 4. Each column of the matrix is 
reserved to a user who, through card 5 and the circuit 18 of the card 5, 
sends to one of the three associated treatment cards 20 (one for each 
rack), the telecontrol orders, providing for the selection of the line 
corresponding to the chosen video signal and its restitution on the matrix 
column corresponding to the appropriate user. The system therefore allows 
controlling the grid by authorizing for each user a choice of any one of 
the signals amongst the fourty-eight signals which are available, without 
deteriorating or deforming the selected signal, the linearity performance 
and the frequency response of which remaining excellent and above all 
without any possibility of interference of one output line with another, 
each of the lines being entirely uncoupled with regards to those which are 
allocated to other users. 
FIGS. 5, 6 and 8 illustrate, in a first variant, the structure of cells E, 
C and S respectively, FIG. 7 facilitating the understanding of the 
operation of the commutation cells C according to FIG. 6. 
illustrates one of the input cells E shown at connection point 24 of the 
coaxial cables 4 and 4' with one of the commutation cards 3, conveying to 
the card one of the signals received from the associated input card 1, a 
resistor 25 of small value connected to an output transistor 26 biased by 
a resistor 27 and supplying with a low impedance an output signal adapted 
for feeding in parallel and via a conductor 28 the assembly of commutation 
cells C situated on the one and same line of the portion of matrix of FIG. 
4. The conductor 28 corresponds in FIG. 1 to the straps 12 which are shown 
here. 
The signal thus collected at the input of any cell C does not flow normally 
through it, at least as long as the commutation order incoming from stage 
R and addressed to the concerned cell has not been received by the latter. 
To this effect, cell C, the diagram of which is shown in FIG. 6, receives 
the signal via lead 28, which flows or not through diode 29 according to 
whether the diode is inhibited or not as a function of the state of 
another diode 30 connected via a lead 31 to the conversion stage R of the 
telecontrol signals. If diode 29 is conductive, the signal received feeds 
via lead 32 a transistor 33 biased by a resistor 34 and outputting at 35 
an amplified signal. The amplified signal is then applied to the output 
cell S (FIG. 8) via a resistor 36 and a transistor 37, the base of which 
is connected to ground.. via a lead 38. The output signal on the collector 
of the transistor 37 is then conveyed by a lead 39 to the output card 5 
corresponding to the point of contact 10 of curd 5 with the commutation 
card 3. 
FIG. 7 shows schematically the operation of the commutation cell C between 
input 28 and output 35. The diodes 29 and 30 and the transistor 33 are 
represented by switches with a synchronized control, in such manner that 
switches 29 and 33 are simultaneously opened when 30 is closed, and vice 
versa. In fact, whatever the quality of the components used, there remains 
in parallel on the terminals of the latter an interference capacity, 
through which can be established, in the opened position of switches 29 
and 33, a leakage current, so that if switch 30 did not exist a residual 
signal would still be transmitted to the output lead 35, disturbing the 
operation of the system. On the contrary and due to switch 30, when 29 
(and 33) are open, 30 closed, any possible leakage current through the 
interference capacity established on 29 is directed to ground, thus no 
signal is delivered to the output lead 35. It is therefore precisely on 
this principle that the circuit of FIG. 6 operates, with the advantages 
pertaining to it as regards the closing or opening, strictly "all or 
nothing", of the corresponding commutation cell. 
FIG. 9 shows the details, in the same embodiment, of the conversion stage R 
receiving from line 10 via the output card 5 associated therewith the 
control orders for the required commutation of any one of cells C of the 
corresponding column, at the level of the line of the matrix which 
receives the input signal to be transmitted. 
The telecontrol signals are notably decoded in the treatment card 20 which 
they reach through lead 19 (FIG. 3) and are then treated by a 
microprocessor which, after selection of the address of the cell C to be 
commuted, sends to it the necessary order via lead 23. Each conversion 
stage R includes to this effect a shift register 40, to which are applied, 
respectively, by leads 41 and 42 the clock and loading signals, while a 
series signal is introduced at 43 so as to select the output of the 
corresponding register precisely at the address of the cell to be 
commuted. Due to the connection 22 and to circuit.....21, one can 
simultaneously take in charge other information for, for example, for 
carrying out counting operations or establishing prohibitions, authorizing 
the commutation only under certain conditions and only for certain users. 
Finally, FIG. 10 shows, also for the same embodiment, the particular 
structure of the selection circuit 14 provided on each output card 5 which 
allows transmitting to the transmitter circuit 15 the only signal received 
from the matrix via cells E, C and S according to the hereabove indicated 
process. 
In this Figure, one sees again the output lead 39 of cell S which transfers 
from the commutation card 3 to the output card 5, at the point of contact 
10 of the cards, the selected signal coming thus, according to case, from 
any one of cards 3, 3a,...3n and interesting any one of cards 5, 5a,...5m. 
Circuit 14 includes to this effect n diodes 45, 45a,...45n, mounted in 
such manner connected by a lead 44 to a corresponding point 10, to a 
common biasing resistor 46 and to a capacitor 47, for delivering the 
signal at the output of the circuit on lead 48 which sends it back to the 
input of transmitter 15. 
Cells S (FIG. 6) form in fact in the example described the 
voltage-controlled current generators, this presenting the advantage of 
eliminating any disturbance possibility due to the resistance of the 
contact at point 10 of cards 3 and 5, and particularly by the series 
resistance represented by circuit 14, thereby eliminating the effects of 
the non linear characteristic of the diodes used. In this respect, one 
should note that if none of cells C of a column of the matrix is in 
service, no current will flow from the corresponding cell S, and this will 
shut didoes 45 in circuit 14. Due to the current generator constituted by 
this cell, a slight voltage difference between cards 5 and 3 is not added 
to the usual signal; therefore, there is no risk of crosstalk at the level 
of the output cards between the signals passing through them. 
FIG. 11 shows an alternative embodiment to the electronic diagram shown in 
FIG. 3, showing how the transmission of signals from an input card 1 to an 
output card 5 and from the latter to the twin-line lead 6 is carried out. 
In FIG. 11 reference numerals identical to those used in FIG. 3 are used 
in order to designate the members playing the same roll and reaching the 
same result in both Figures. 
Particularly, and as shown in FIG. 12, the diodes in parallel provided in 
the discriminator circuit 14 receiving on leads 14 from the points of 
contact 10 between the commutation cards and the output cards, are 
replaced here by switches 49, 49a,... 49n constituted by appropriate 
electronic micro-relays, for example, of the analog commutator type CMOS, 
whose control of the opening as well as of the closing is determined by an 
order incoming from the associated conversion stage R. 
In this variant however, the conversion stage R of the control signals 
providing for the commutation of cell C of card 3 is carried by the output 
card 5 and receives directly from the treatment card 20 the corresponding 
orders via lead 23. In this case, the conversion stage schematically shown 
in FIG. 13 includes once again a shift register 40 with an input lead 41 
for a clock signal and an input lead 42 conveying loading signals of the 
register, the control signal selecting the address of cell C to be 
commuted in the register being conveyed by lead 43. The register delivers 
two series of signals, respectively, to the selection circuit 14 as in the 
previous variant, and to a decoder D, carried by the associated 
commutation card 3, the signal being transmitted to the decorder circuit 
by a lead 50. The decoder D schematically shown in FIG. 14 includes a 
treatment circuit 41 for the received signals 50 and as many outputs 52 as 
the matrix includes cells C, in order to cause, as a function of the order 
receiveD from a given user, the transmission of the selected signal. 
Decoder D plays therefore, at the level of that portion of the matrix, the 
role of conversion stage R in FIG. 4.