Wave transmission lines and networks – Coupling networks – With impedance matching
Reexamination Certificate
2000-01-06
2001-10-23
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
With impedance matching
C333S001000, C333S02400C
Reexamination Certificate
active
06307445
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a circuit arrangement for forming an impedance match of transmission lines. The circuit arrangement includes a control stage, a dynamic input impedance formed by resistances and a transformer provided with primary and secondary coils. The control stage and the input impedance are connected to the poles of the transformer's secondary coil while transmission lines all with a different characteristic impedance are connected one by one to the poles of the transformer's primary coil.
BACKGROUND OF THE INVENTION
In PCM systems, signals can be conducted from and to a transmission unit either e.g. on an E
1
line in accordance with the European standard or e.g. on a T
1
line in accordance with the American standard. The E
1
line can be e.g. a 75 &OHgr; coaxial cable or a 120 &OHgr; twisted pair cable, while the T
1
line may be e.g. a 100 &OHgr; pair cable. Earlier, the circuit board of the transmission unit was only provided to be compatible either with an E
1
or with a T
1
line, but nowadays the IC circuits on a transmission card are suitable for use both with E
1
and T
1
lines, whereby both these lines can be wired to the circuit board and either line may be chosen for electric connection to the transmission circuit.
In the transmission unit of a PCM system, e.g. in the transmitter/receiver transmission unit of a Pan-European GSM mobile communications system, the transmission circuit board must be matched to the characteristic impedance of the transmission cable used to bring about the desired signal and impedance levels. For example, cables of the E
1
line or T
1
line mentioned above may be used as the transmission line. For matching of different line impedances of a transmission card which is as versatile as possible, it is known to use e.g. a transformer match as the one shown in
FIG. 1
in the appended drawing, the primary coil having a center tap that is connected to an operating voltage +V,
FIG. 1
illustrates an impedance matching line controller circuit having a control stage
5
for controlling the transmission of a cable, resistors R and a transformer having primary and secondary coils where there is an intermediate output in the secondary coil, whereby a suitable output resistance R of the primary coil is set at different transformation ratios of the transformer T
120
, T
75
, TCOMM, for example, a 75 &OHgr; output resistance T
75
is set at a transformation ratio of 1:1.26 to be suitable for a 120 &OHgr; cable or at a transformation ratio of 1:1.15 for a 100 &OHgr; cable. It is a problem with this implementation that a big transformer is required.
It is known from patent publication FI-95182 to use a line controller circuit implemented without any separate intermediate output in the secondary coil of the transformer, as shown in
FIG. 2
of the appended drawing having similar components to
FIG. 1
, for the impedance match between the intermediate output circuit and the transmission line. In the line controller circuit of the publication, the output impedances R
opt
and the transformer's numbers of turns n
opt
, are matched so that the circuit will provide simultaneously the signal level required by two transmission lines each having a different impedance. It is a problem with state-of-the-art impedance matches that it is usually possible to match them simultaneously to be suitable only for two different characteristic transmission line impedances.
SUMMARY OF THE INVENTION
The purpose of this invention is to implement a flexible impedance match for characteristic impedances of different transmission lines, e.g. for impedances of the E
1
lines and T
1
lines of a PCM system.
This impedance match of a novel type is achieved through such circuit arrangements according to the invention.
The invention is based on the idea that the input impedance of the transmission circuit in a PCM system is chosen to match the characteristic impedance of a transmission line chosen with a digitally controlled analog switch connecting an analog signal. With a connection in parallel of resistances chosen with a suitable analog switch, the input impedance can be matched to several characteristic impedances of different transmission lines in connection with the electric connection of the transmission line to the transmission circuit. In one embodiment of the invention connecting of transmission lines is also performed in a connector part including a connector strip, preferably a pin head connector, and a counterpart which can be attached to it in two different positions. The counterpart in its first position connects to the transmission card only the first twin wire of two twin wires and in its second position it connects only the second one. In its first and second positions the counterpart has the same side against the connector strip. In addition, the second position of the counterpart is achieved by turning the counterpart through 180° in the plane of that side which is against the connector strip. In this way different lines, such as e.g. E
1
lines in accordance with the European standard or e.g. T
1
lines in accordance with the American standard are separated from each other by a connector strip, and the desired signal routes are short-circuited by a counterpart which is placed on top of the connector strip. The signal routes are changed by turning the counterpart.
It is an advantage of such an impedance match that it is simple and being a single connection it is very stable.
It is an advantage of the impedance match and of the connection arrangement that the connection of desired transmission cables to the transmission circuit is simple. Changing of the cable connection is also easy.
REFERENCES:
patent: 5017818 (1991-05-01), Dohogne
patent: 5771262 (1998-06-01), Benayoun et al.
patent: 5896417 (1999-04-01), Lau
patent: 0 240 454 (1987-10-01), None
patent: 0 258 029 (1988-03-01), None
patent: 95182 (1992-10-01), None
patent: 6275346 (1994-09-01), None
patent: 7212168 (1995-08-01), None
patent: 8107325 (1996-04-01), None
patent: 8123593 (1996-05-01), None
patent: 8195637 (1996-07-01), None
patent: 94/10750 (1994-05-01), None
Mäkinen Olli-Pekka
Pasanen Timo
Pyyhkälä Jouni
Altera Law Group LLC
Lee Benny
Nokia Networks Oy
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