Measuring device for the interface of a transmission path with full-duplex transmission in the common carrier duplex process

A measuring device for the interface of a transmission path with full-duplex transmission in the common carrier duplex process. A highly integrated interface unit is connected to the interface via a hybrid set and a transmitter on one side. A line termination or a network termination is connected as the test object on the other side. In order to perform measurements on the test object with such a measuring device relatively easily and accurately, a device simulating the arrangement of a hybrid set, a transmitter and a line or network termination is provided and with its connected to the highly integrated interface unit via a high-resistance differential amplifier, and its output connected to an input of a subtractor. Another input of the subtractor is connected to the interface via an additional differential amplifier. The output of the subtractor is connected to a measurement system.

FIELD OF THE INVENTION 
The present invention relates to full-duplex transmission path interface 
measuring devices. 
BACKGROUND INFORMATION 
As described in U.S. Pat. No. 4,989,202, an ISDN (integrated services 
digital network) transmission path between the transmission line and a 
network has an interface. It is also known (see "Siemens KMT Report," no. 
14, order no. E 80001-V331-W54, pages 6 and 7) that measurements can be 
performed on this interface and an appropriate measuring device can be 
provided for this purpose. For example, frequency-dependent measurements, 
functional tests and even jitter measurements can be performed with this 
measuring device. An ISDN data transmission line is a special form of a 
transmission line with full-duplex transmission in the common carrier 
duplex process. 
According to European Patent Application No. 9,592 A1, a differential unit 
in a transmission and receiving device connected to a duplex line is 
provided for receiving signals. Two signals are sent to this differential 
unit, namely the transmission signal of its own transmission and receiving 
device and the complete signal that is transmitted on the duplex line and 
which consists of its own transmission signal plus a signal to be received 
from another transmission device. The task of the differential unit is to 
subtract its own transmission signal from the composite signal of the 
duplex line and in this way to make it possible to receive only the signal 
of the other transmission device. Thus, cross-talk from its own 
transmission signal to the received signal is suppressed. 
SUMMARY OF THE INVENTION 
The present invention relates to a measuring device for the interface of a 
transmission path with full duplex transmission in the common carrier 
duplex process, whereby a highly integrated interface unit is connected to 
the interface via a hybrid set and a transmitter on the one hand and a 
line termination (LT) or a network termination (NT) as the test object on 
the other hand. 
An object of the present invention is to provide a means to accurately and 
simply perform physical measurements on the interface during transmission 
operation. This object is achieved according to the present invention by 
providing a device that simulates the arrangement consisting of a hybrid 
set, a transmitter and a line or network termination and which contains a 
high-resistance differential amplifier that is connected at the input to 
the transmission outputs of the highly integrated interface unit and at 
the output to an input of a subtractor via another high-resistance 
differential amplifier. Another input of the subtractor is connected to 
the interface via an additional high-resistance differential amplifier, 
and a measurement system of the measuring device is connected to the 
output of the subtractor. 
An important advantage of the measuring device according to the present 
invention is that by using the simulating device and the subtractor, it is 
possible to analyze only the signal transmitted by the respective test 
object because the signals going to the test object and information in the 
subtractor are filtered out, so that only the signal sent by the 
measurement object is available and can be analyzed easily by a 
measurement system of the measuring device. 
With the measuring device of the present invention, the device simulating 
the arrangement of a hybrid set, a transmitter and a line or network 
termination may have various designs. It is particularly advantageous--for 
the purpose of substantially eliminating the signals sent to the test 
object--if the simulating device has a hybrid set identical to the hybrid 
set of the transmission path, a transmitter identical to the transmitter 
of the transmission path and a termination with electric properties 
identical to those of the line or network termination of the transmission 
path. 
To achieve the advantages of the measuring device of the present invention 
even when the transmission path has an attenuating device at the 
interface, it is advantageous for the simulating device of the measuring 
device to have, between the identical transmitter and the identical 
termination, an attenuating device with the same electric properties as 
the attenuating device of the transmission path. 
It may also be advantageous to have an attenuation arrangement with effects 
identical to those of the attenuation device of the transmission path 
connected downstream from the additional high-resistance differential 
amplifier in a transmission path with an attenuation device at the 
interface in the device simulating the measuring device.

DETAILED DESCRIPTION 
FIG. 1 shows a transmission path 1 with an interface 2, which may be an 
interface of an ISDN transmission path, for example, with full duplex 
transmission in the common carrier duplex process. A highly integrated 
interface unit 3 is connected at the interface in a known way. 
Specifically, the highly integrated interface unit 3 is connected via two 
transmission outputs 4 to a hybrid set 5. Hybrid set 5 is connected via a 
downstream transmitter 6 to interface 2 to which a test object 7 is also 
connected. This test object may be a line termination (LT) or a network 
termination (NT). 
As FIG. 1 also shows, a device 8 containing a high-impedance differential 
amplifier 9 at the input end is connected to transmission outputs 4 of the 
highly integrated interface unit 3. Downstream from the differential 
amplifier 9 is a hybrid set 10 whose electric properties are identical to 
those of hybrid set 5 of transmission path 1. A transmitter 11 downstream 
from the identical hybrid set 10 is also the same as transmitter 6 of 
transmission path 1. A termination 12 whose electric properties are 
identical to those of test object 7 is connected to the transmitter 11. At 
the input of the identical termination 12 is connected another 
high-impedance differential amplifier 13 whose output is connected to an 
input 14 of a subtractor 15. 
Another input 16 of subtractor 15 is connected to interface 2 via an 
additional high-impedance differential amplifier 17. A measurement system 
19 of the measuring device is connected to an output 18 of subtractor 15 
and may be suitable for performing jitter measurements, for example. 
In the area of interface 2 in FIG. 1, an arrow with the designation 
U.sub.outward indicates that a signal transmitted from the interface unit 
3 via hybrid set 5 and transmitter 6 to test object 7 is available at 
interface 2 and thus also at the output of the additional differential 
amplifier 17. Furthermore, the signal U.sub.return sent back is available 
at interface 2. Both signals U.sub.outward and U.sub.return are available 
at the output of the additional differential amplifier 17, because it has 
a gain of 1, and are detected via input 16 of subtractor 15. However, only 
signal U.sub.outward delivered at transmission outputs 4 of highly 
integrated interface unit 3 is sent to input 14 of subtractor 15 via 
differential amplifier 9, identical hybrid set 10, identical transmitter 
11 and the additional high-resistance amplifier 13. Therefore, due to the 
formation of a difference, only the U.sub.return signal which contains 
information from or regarding test object 7 appears at output 18 of 
subtractor 15. The signal U.sub.return can thus can be analyzed by 
measurement system 19, for example, for phase jitter. Therefore, the 
U.sub.outward signal does not interfere with measurement system 19. 
The embodiment of FIG. 2, in which components corresponding to those in the 
embodiment of FIG. 1 are labeled with the same notation, differs from that 
in FIG. 1 in that an attenuation device 21 identical to the attenuation 
device 22 in transmission path 23 between the transmitter 6 and interface 
2 is provided between the identical transmitter 11 and termination 12 in 
the simulating device 20. The identical attenuation device 21 assures that 
a signal U.sub.outward that corresponds to the signal U.sub.outward at 
interface 2 is sent to input 14 of subtractor 15. Only the signal 
U.sub.return is measured by the measurement system. 
The embodiment according to FIG. 3 differs from that of FIG. 2 only in that 
an attenuation arrangement 30 with the same electric properties as 
attenuation device 22 is connected to the output of the additional 
high-resistance differential amplifier 13 in a simulating device 31, which 
thus again assures that a signal U.sub.outward which corresponds to a 
matching signal at interface 2 is available at input 14 of subtractor 15 
so that only the signal U.sub.return of test object 7 is provided at 
output 18 of subtractor 15.