Switching matrix for selectively connecting incoming signals to desired output paths

The invention relates to a circuit arrangement for passing of blocking signals having wide band width with the use of at least one electronic switch. The circuit is a very simple arrangement, and provides for a plurality of modulators, or at least one modulator prior to the switching, and wherein the electronic switch is utilized is a logical linkage. The circuit is particularly adaptable for use in television circuits for distributing television signals.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to a circuit arrangement for switching or 
blocking wide band width signals utilizing at least a single electronic 
switch, and the circuit is particularly adaptable for distribution of 
video signals. 
2. Description of the Prior Art 
Cross bar distributors for video signals are known, as for example, in 
German AS No. 2,121,611. In the construction of such a distributor because 
of the wide band width of the signals to be transmitted, great care must 
be undertaken to meet the requirements to prevent non-linear distortion 
and high cross-talk continuation. If mechanical switches are not used as 
cross points, it is possible to utilize a cross bar distributor for 
example, with active cross points and corresponding control or drive 
circuits. Special circuits are required for such video cross points so as 
to be able to retain the linearity and cross talk attenuation 
requirements. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a circuit arrangement 
for switching of wide band video signals which utilizes electronic 
switches and which can be constructed in a very simple manner. The circuit 
arrangement is designed to include a modulator which is connected prior to 
the electronic switch or switches and the modulator modulates a carrier by 
the signals so that the information will occur at the time when the 
carrier has been modulated to a zero value, and wherein the electronic 
switch or switches are designed as logical linkages. The advantage of the 
electronic switches of the invention result in a very simple circuit and 
allow less distortion and cross talk than circuits of known arrangements. 
The circuit is particularly useful for wide band video signals. 
When the electronic switches or cross points of a switching matrix of a 
cross bar distributor in which input lines may be selectively connected by 
way of the cross points with output lines, the invention provides for a 
respective modulator to be connected to the input lines and a respective 
demodulator to be connected to the output lines. In the case of modulation 
of the signals, the upper limiting frequency is greater than in the 
original position of the signals, the requirements and demands limitations 
of the cross points are significantly lowered. 
The demodulator can be respectively connected directly to the output of the 
electronic switch or switches, and directly to the output lines. 
Alternatively, the respective signal transmissions segment can be moved 
between the electronic switch and the output line of the switching matrix, 
and the demodulator can then simultaneously serve as the transmission 
modulator for the signal transmission. 
If in the switching matrix a plurality of output lines is greater than the 
number of input lines, or if the plurality of participants is greater than 
the plurality of the programs in a program distribution system, then 
additional advantage results in that fewer modulators are required than 
would be the case if there was an allocation of modulators to individual 
signal transmission segments. 
An additional development of the invention provides that the modulator is 
designed as a frequency modulator, so that the frequency modulated signals 
can be transmitted by way of an optical transmission path such that the 
light wave guide transmission system and the circuit arrangement operate 
with the same frequency modulated carrier. Such an arrangement is 
particularly suited for distribution of TV signals. 
Other objects, features and advantages of the invention will be readily 
apparent from the following description of certain preferred embodiments 
thereof, taken in conjunction with the accompanying drawings, although 
variations and modifications may be effected without departing from the 
spirit and scope of the novel concepts of the disclosure, and in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The switching matrix of the invention illustrated in FIG. 2 is constructed 
as a cross bar distributor, and has a plurality of m input lines which 
cross a plurality of n output lines. A plurality of n.m coupling points or 
cross points are provided for the optional connection of input to output 
lines. In FIG. 1, the couplings or cross points are designated as K.sub.11 
. . . K.sub.nm, and are shown adjacent the crossing points. 
A plurality of modulators M.sub.1 . . . M.sub.m are connected to the inputs 
E.sub.1 . . . E.sub.m of each of the input lines m, as shown. A plurality 
of optical transmitters S.sub.1 . . . S.sub.n are respectively connected 
to each of the outputs A.sub.1 . . . A.sub.n of each output line n, as 
shown. Optical lines L.sub.1 . . . L.sub.n are respectively connected to 
the outputs of each of the optical transmitters S.sub.1 . . . S.sub.n. 
Because it is not the video signal itself, but rather a sub-carrier 
frequency modulated with the video signal which passes over the matrix 
cross points, simple logical gates can be employed as the matrix switches. 
Such simple switches, in addition to providing a very simple arrangement, 
also provide that very low power consumption will occur, which is of 
particular advantage. 
A further advantage of the switching matrix arrangement illustrated in FIG. 
1 is that the relatively high lower limiting frequency of approximately 5 
MHz exists. In a video coupling field of the conventional type, on the 
other hand, a lower limiting frequency occurs such as at a few Hz, so that 
a relatively great outlay of equipment and cost can occur in such prior 
art systems, due to the expensive control signals required in the control 
or drive circuit of such systems. 
In addition to its advantage in the switching matrix, the use of a 
frequency modulated sub-carrier can also prove to be particularly 
advantageous in the optical transmission paths, as for example, in 
providing low non-linear distortion in the light emitting diodes and also 
in providing low signal-to-noise ratios so that transmission can occur 
over great distances. 
The use of logical switch linkages as coupling points is not only 
advantageous in operation using frequency modulated signals, but other 
types of modulation can also be used in which the information occurs 
during the time the carrier has been modulated to zero such as in PFM or 
pulse frequency modulation, PM or phase modulation, PPM or pulse phase 
modulation, or PDM or pulse duration modulation. 
One or more connection lines in the form of a glass fiber conductor passes 
from the outputs of the switching matrixes to each subscriber. Also, a 
return channel can be provided from the subscriber to the central 
switching matrix so that a subscriber can select which ones of the wide 
band signals available at the central station is to be switched to the 
glass fiber conductor which connects him with the station. 
FIG. 2 is a greater detail view of the switching matrix illustrated in FIG. 
1. Various input video signals are supplied respectively to the FM 
modulators M.sub.1 . . . M.sub.4. The outputs of these modulators M.sub.1 
. . . M.sub.4 are respectively connected to the inputs of a plurality of 
limiters B.sub.1 . . . B.sub.4, which can be designed as comparators. It 
is advantageous if the signal passes through zero during the switching 
time of the switching linkage, which can be very fast. In FM and PM modes, 
this advantage is achieved, due to the transition to "rectangular-FM" or, 
respectively, "rectangular-PM" by the use of amplitude limitation and 
amplification which occurs in earlier stages. 
The switching at the crossing points is accomplished in a semiconductor 
chip G which contains four switching linkages which are respectively 
designed as NOR elements. In each of these NOR elements G.sub.n1 . . . 
G.sub.n4, one of the two inputs is connected to the output of one of the 
limiters B.sub.1 . . . B.sub.4 on the input lines m, and a second input is 
received from control lines St1 . . . St4. For example, if a logic level 1 
occurs on the control input line, the switch G.sub.n will be blocked, and 
a signal level of zero on the control line St allows the input on the line 
m to be supplied to the output line n. Each of the NOR elements G.sub.n 
are connected to the associated output line n. It is to be realized that a 
plurality of the chips G will include a plurality of the NOR elements 
G.sub.n for each of the output lines, but in FIG. 2, only one output line 
is illustrated for simplicity. 
The output line n is connected to an optical transmitter S.sub.n which is 
connected to the optical line LN. 
So as to maintain the switching time as small as possible, the switching 
linkages are constructed in ECL technology, and are such that their 
outputs can be directly switched in parallel in the manner of so-called 
wired OR circuits without the use of an additional OR element. 
Logical level zero at the control input assures that the linkage functions 
as an inverter for the signal to be connected through the switching path. 
If the NOR elements are replaced with AND elements, then the logical level 
of 1 on the control lines St will turn the AND elements on and level zero 
will turn them off. 
In a particular arrangement, OR elements or NOR elements formed in TTL 
technology and which utilize an open collector output are particularly 
suited for the circuits of the invention, since an output side junction 
formed as a "wired AND circuit" or as a wired OR circuit is possible, and 
can be utilized. 
Although the invention has been described with respect to preferred 
embodiments, it is not to be so limited as changes and modifications can 
be made, which are within the full intended scope as defined by the 
appended claims.