Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1997-11-26
2001-01-09
Pham, Chi H. (Department: 2731)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S276000, C370S284000
Reexamination Certificate
active
06172992
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to transmission link testing, and more particularly to a measuring device for the interface of a transmission link with full-duplex transmission in two-wire common band operation.
It is known (for example from U.S. Pat. No. 4,989,202) that an ISDN (Integrated Services Digital Network) transmission link has a U interface between the transmission line and a so called network. It is further known (cf. “Siemens-KMT-Report, No. 14, order no. E 80001-V331-W54, pages 6 and 7) to perform measurements on this U interface and to provide a corresponding measuring device for this purpose. This measuring device may be used to perform frequency-dependent measurements, functional tests as well as jitter measurements for example. An ISDN transmission link is a special form of a transmission link with full-duplex transmission in two-wire common band operation.
Furthermore, German patent specification DE 44 23 333 C1 discloses a measuring device for the interface of a transmission link with full-duplex transmission in two-wire common band operation. Connected to said interface are a large-scale integrated interface module, via a hybrid circuit and a transformer, on the one hand, and a line termination or a network termination as the test object on the other hand. The measuring device includes means simulating the arrangement of hybrid circuit, transformer and line or network termination, the input of said simulating means being connected to the transmission outputs of the interface module via a high-impedance differential amplifier and the output of said simulating means being connected to an input of a subtractor via a further high-impedance differential amplifier. A further input of the subtractor is connected to said interface via an additional high-impedance differential amplifier; the output of the subtractor communicates with a measuring system.
The invention is based on a measuring device of this type and it is the object of the invention to permit jitter measurements to be precisely performed on the interface of a transmission link with full-duplex transmission during the ongoing transmission using a conventional jitter measuring device.
BRIEF SUMMARY OF THE INVENTION
For accomplishing this object, the invention proposes a measuring device in which a differentiator followed by a comparator is coupled to the subtractor and a jitter measuring device as a measuring system is post-connected to the comparator.
The essential advantage of the measuring device according to the invention is that it also permits an unambiguous determination of phase jitter in the case of ISDN data signals with multivalid codes since the differentiator and the comparator post-connected to it only detect relevant data signals; such being characterized in that they feature the full signal level swing predetermined by the respective code whereas all other data signals are ignored during phase jitter measurement.
In order to realize a specially simple differentiator which may also be produced at low cost, it is considered advantageous to form said differentiator from a series connection of at least one capacitor, at least one inductor and at least one resistor.
The differentiated output of the differentiator may be transmitted to the comparator in a particularly simple and thus advantageous manner if a voltage dropping at the resistor is applied to the comparator.
Differentiators which are simple from a point of view of circuit engineering are bandpass filters for example for which reason it is considered advantageous if the differentiator is a bandpass filter. A further advantage of a bandpass filter is that low-frequency interference signals, e.g. caused by the interface, are suppressed by the bandpass filter so as not to affect the jitter measurements.
The invention is illustrated in more detail in the accompanying drawings.
REFERENCES:
patent: 4320516 (1982-03-01), Kammerlander
patent: 4819080 (1989-04-01), Cucchietti et al.
patent: 5923706 (1999-07-01), Marz
patent: 5936946 (1999-08-01), Hoffmann
Duong Frank
Gray Francis I.
Lenihan Thomas F.
Pham Chi H.
Tektronix Inc.
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