FI103231B - Impedance adjustment for transmission lines - Google Patents

Description

1 103231

Impedance matching of transmission lines

Field of the Invention

The invention relates to a circuit arrangement for forming an impedance matching 5 of transmission lines. The circuit arrangement comprises a control stage, a dynamic input impedance of resistors and a transformer with primary and secondary windings. The control stage and the input impedance are connected to the poles of the secondary winding of the transformer and the transmission lines having different specific impedances are connected one by one to the poles of the primary winding of the transformer.

BACKGROUND OF THE INVENTION In PCM systems, signals from the transmission unit and the transmission unit can be derived, for example, by a European standard 15 E1 line or, for example, by an American standard T1 line.

For example, the E1 line can be a 75 Ω coaxial cable or a 120 Ω twisted pair cable, and the T1 line can be, for example, a 100 Ω twin cable. Previously, the transmission unit's circuit board was only equipped with either E1 or T1 lines, but today the ICs on the transmission circuit board are suitable for use with both E1 and T1 lines, allowing the circuit board to derive both of these lines and select which line is electrically connected to the transmission circuit.

In the transmission unit of the PCM system, e.g. In a transceiver unit of a base station of a GSM mobile communication system, in order to achieve the desired signal and impedance levels, the transmission circuit board must be adapted to the characteristic impedance of the transmission cable used. For example, the above-mentioned E1 line or T1 line cables may be used as transmission lines. For example, it is known to use the "30 transformer adapter shown in FIG. 1 of the accompanying drawing, with a secondary winding output, whereby a different transformer ratio is used to set a terminal resistor suitable for the transmission line, for example, 75 Ω terminating resistor or 1: 1.15 for 100 Ω cable. The problem with this implementation is that it requires an iso-35 transformer.

2 103231

It is known from FI-95182 to use a line control circuit implemented without a separate intermediate take-off of the transformer secondary winding shown in Figure 2 of the accompanying drawing for impedance matching between the output circuit and the transmission line. The output line impedances 5 Ropt and the transformer RPM are matched in the line controller circuit of the publication so that the circuit simultaneously provides the signal level required by two different impedance transmission lines. The problem with prior art impedance adaptations is that it is generally possible to adapt them simultaneously to only two specific impedances of a transmission line.

10

BRIEF SUMMARY OF THE INVENTION The object of the present invention is to provide a flexible impedance matching for specific impedances of different transmission lines, for example different impedances of E1 lines and T1 lines of a PCM system.

This new type of impedance matching is achieved by an inventive circuit arrangement, characterized in that, for generating a resistive input impedance, the circuit arrangement comprises a processor and means for implementing the matching.

The invention is based on the idea that the input impedance of a PCM system trans-20 mission circuit is selected by a digital-controlled analog signal coupling analog switch to match the characteristic impedance of a selected transmission line. By selecting the appropriate parallel switch of resistances, the input impedance can be adapted to a plurality of different transmission lines. r - the characteristic impedance of the transmission line transmission circuit during the electrical connection.

The advantage of such an impedance match is that it is simple and, once in a single turn, very stable.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the preferred embodiments, with reference to the examples of Figures 3, 4 and 5a to 5c in the accompanying drawings, in which: Figure 1 shows an impedance matching circuit of a prior art transformer; 3 103231 Fig. 2 shows a prior art line controller circuit adapted to two specific impedances of a transmission line; Figure 3 shows an impedance matching according to the invention in connection with an exemplary circuit diagram; Fig. 4 is a circuit diagram of a line controller circuit according to the invention; and Figures 5a-5c illustrate a circuit diagram of various line impedance adaptations of a line controller circuit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION In the following, the invention will be described in more detail in light of the preferred embodiment of the invention with reference to Figures 3, 4 and 5a to 5c.

Figure 3 is an exemplary circuit diagram of an impedance matching of transmission lines to a transmission circuit according to the invention. In the illustrated example of the input side of the impedance matching selected processor-controlled analog switches 15, which. In the figure, transfer cables from the outside of the transmission unit, which in the case of Figure 3 are marked by the cable impedance, are connected to the switching arrangement 17. In the case of Fig. 3, the connection of symmetric transmission lines such as twisted pair cables and twisted pair cables is provided with 100/120 markers and asymmetrical transmission lines such as coaxial cables with li-20 terminals 75 and ground potential markings. The impedance values shown are set by way of example only to illustrate the connections of the switching arrangement 17 according to the invention. Of course, cables with different impedances than those described above can also be connected to the coupling arrangement 17. 3. The arrangement 17 shows the signal path connection of symmetrical 100/120 Ω cables by means of short circuits 16. The line control unit 11 in the figure connects the transmission lines to the other transmission circuit. The transmission side Tx of the transmission circuit is connected over the output resistors R and the transformer 12 to a switching arrangement 17 which is further connected to the transmission circuit receiving side Rx through an impedance matching according to the invention. 4 and 5a to 5c illustrate this impedance matching 30 in the following.

Fig. 4 is a circuit diagram illustrating an impedance matching of a line controller circuit according to the invention. The selected transmission line is connected to the terminals of the primary winding of the transformer 13 and the input resistor selected by the switch 14 is connected to the secondary winding terminals of the transformer 13 and to the input of the line control unit 11. The processor 15 controls the switches 14a and 14b of the analog switch 14 to connect the resistors R1, R2 and / or R3 required for the impedance matching of the impedance to achieve resistive input impedance of the line controller circuit according to the invention as described in more detail below. At different switch positions, the input impedance consists of 5 resistors R1, a parallel connection of resistors R1 and R2, a parallel connection of resistors R1 and R3, or possibly also a parallel connection of resistors R1, R2 and R3. The values of resistors R1, R2, and R3 are selected to be those required by the specific impedance of the transmission line to be matched.

By way of example, the following illustrates the impedance matching of transmission lines having specific impedances of 75, 100, and 120 illä with the line control circuit according to the invention in Figs. 5a to 5c. Figure 5a shows a 120 Ω transmission line arrangement for line control unit 11. The switches 14a and 14b shown in Figure 4 are both controlled by processor 15 to the open position, whereby the input impedance of the circuit is formed solely by resistor R1. The value of the resistor R1 15 may be selected, for example, to provide 121 Ω for matching the impedance of the transmission line 120 Ω: η.

Figure 5b shows a 75 Ω transmission line arrangement for line control unit 11. The processor 15 then controls the switch 14b in the closed position and the switch 14a in the open position shown in Figure 4, whereby the circuit input impedance 20 is formed by a parallel connection of resistors R1 and R2. In order to provide matching of the impedance of the transmission line 75 Ω: η, the values of resistors R1 and R2 can be selected, for example, R1 = 121 Ω and R2 = 182.2 Ω.

Fig. 5c shows a 100 Ω transmission line arrangement for the line control unit 11.

; The processor 15 then controls the switch 14a in the closed position shown in Fig. 4 and the switch 14b in the open position, whereby the input impedance of the circuit consists of a parallel connection of the resistors R1 and R3. For example, for the impedance matching of the transmission line 100 Ω: η, the values of resistors R1 and R3 may be selected as R1 = 121 Ω and R3 = 481.2 Ω.

For the line controller circuit of the present invention, it is preferable to select a broadband, digitally controlled analog switch, which is as stable as possible in frequency, temperature, etc. For example, the switch may be of the commercially available type MAX392. Due to the dynamic input impedance control, the same transformer can be used in the line controller circuit for all line types. Transformers 12 and 13 of Figure 3 are preferably 1: 1 or 1: 2 transformers, but transformers of other conversion ratios are also possible.

The coupling arrangement 17 shown in Fig. 3 preferably consists of a connector part comprising a connector strip, preferably a stud, and a counter part that can be attached thereto in two 5 different positions. The counterpart engages a first pair of conductors in a first position and a second pair of conductors in a second position on the transmission card. In the first and second positions, the side facing the terminal block of the counterpart is the same. Further, the second position of the counterpart is achieved by rotating the counterpart 180 ° in the plane of the 10 sides facing the terminal block. Thus, different lines, such as, for example, European standard E1 lines or, for example, American standard T1 lines, are separated from each other by a terminal strip, with a matching part short-circuiting the desired signal paths. Changing the signal paths is accomplished by turning the counterpart. Preferably, the counterpart comprises a short-circuit piece 15 or an access portion and a short-circuit board such as a circuit board. It is clear that the impedance matching according to the invention is also suitable for use with other types of transmission line switching arrangements.

The impedance matching according to the present invention is particularly suitable for implementing a precise reception matching, but can also be used to fit a transmission circuit to a transmission line.

The drawings and the description related thereto are only intended to illustrate the idea of the invention. The details of the line controller circuit according to the invention may vary within the scope of the claims. Although there is an invention. In the case of an input impedance consisting mainly of a parallel connection of three resistor combinations 25 described above, multiple matching resistor can be used in the matching circuit, whereby several characteristic impedances of different transmission lines can be fitted to the transmission circuit. The characteristic impedances of the transmission lines presented above in connection with the description of the invention are only intended to illustrate the idea of the invention. Of course, the impedance matching according to the invention is also suitable for use in matching the characteristic impedance values other than those described above.

Claims (5)

103231 A circuit arrangement for forming an impedance matching of transmission lines comprising a control stage (11), a dynamic input impedance formed by resistors and a transformer (13) having primary and secondary windings such that the control stage (11) and the input impedance are connected to transmission lines having characteristic impedances are connected one by one to the terminals of the primary winding of the transformer (13), characterized in that, for generating resistive input impedance, the circuit arrangement comprises a processor (15) and elements 10 (14, 14a, 14b). Circuit arrangement according to claim 1, characterized in that the means for implementing the matching comprises an analog switch (14, 14a, 14b) responsive to the control of the processor (15) and a resistive input impedance selected by said analog switch. The circuit arrangement according to claim 1 or 2, characterized in that the input impedance to be selected is different for the specific impedances of the different transmission lines and consists of one or more parallel resistors (R1, R2, R3). Circuit arrangement according to Claim 1, 2 or 3, characterized in that the input impedance is selected on a single-circuit basis when it is electrically connected to the transmission line control circuit. Circuit arrangement according to one of Claims 1 to 4, characterized in that it further comprises a switching arrangement (17) through which transmission lines of different characteristic impedances are connected one by one to the primary winding terminals of the transformer (13), comprising a first and second group of conductors (Tx). , Rx), the first group of conductors comprising at least a first and a second pair of conductors, and a connector part connecting one of the conductors of the first and second groups, which connector part is | interleaves a terminal block mounted on the circuit board and a separate detachable counterpart 30 mounted to the terminals of the first conductor array so that in its first position, the first and second pair of conductors connect only the first pair of conductors to at least one second array conductor (Tx, Rx); in its inverted position 180 degrees from its first position and from the first and second pair of conductors, only a second pair of conductors to at least one conductor (Tx, Rx) of the second group. w 103231