Switching Arrangement for Coupling a Transmitting Unit to a Transmission Line

The present invention pertains to a switching arrangement for coupling a transmitting unit to a transmission line.

For the supply or the removal of signals, connecting leads are often conductively connected with two wire conductors. During couplings of this type, in order to make contact it is necessary each time to remove or pierce the insulation layer of the two wire conductor. A multiple coupling of connecting leads results in damage to the two wire conductor. In addition, the unallowed coupling of unauthorized third parties onto the two wire conductor is easily feasible. In a telephone network utilizing conductive coupling, unauthorized parties can readily switch on. European Patent Publication No. EP-OS 0 417 542 discloses an apparatus for the inductive coupling of sending coils to a two conductor wire which largely eliminates such problems. Therein, a three-limbed ferrite core is utilized, whose yoke, for the insertion of the coupling coil or the two wire conductor is so pivotally arranged, that the two wires of the transmitting line accordingly pass through the center limb and one of the two outer limbs. For example, the coupling coil connected with the transmitting unit surrounds the center limb with several windings. For the transmission of information between two subscriber end units coupled to the transmission line, the transmitter generates a modulated high frequency signal to the primary coupling coil, which signal transforms the transformer, comprised of the coupling coil and the transmission line, and carries same, via the secondary-sided transmission line to the receiving end unit. The primary-sided perceived load Z1 of the transmitter ideally corresponds to the product of the secondary-sided contacting load Z2 and the square of the transmission ratio (N1/N2). Parallel thereto, the relatively small main inductivity of the transformer makes an appearance, which requires an amount of current which exceeds, many times, that of the transformed load or resistance Z1. The main capacity becomes particularly small if the secondary windings, formed via the transmission line, has only a few windings. The inductive coupling is thus problematic only for nonsystem-connected terminal units, which, for example, only have very low supply voltages available and which can supply only small outputs. Normally, with such terminal units only a limited range can be achieved, within which there is a satisfactory signal to noise ratio. If, for example, in order to increase the range, the output to the transmission line is increased, there is a reduction of the life span of the batteries that feed the terminal unit. In terminal units, powered by the network, a correspondingly larger dimensioned current supply unit would have to be provided.

The basis for the task of the present invention is to provide a switching arrangement which avoids the described disadvantages. Particularly, the range between the individual terminal units should be increased, the output removal of the terminal units should be reduced and the signal to noise ratio should be enhanced.

This task is achieved via the measures set forth in the specification and the characterizing portions of the claims. Advantageous embodiments of the invention are also set forth in the specification and the claims.

By the use of the method of this invention and the switching arrangements of the present invention, the amount of current that must be fed to the coupling unit is greatly reduced, which is particularly favorable for non-system-connected operated terminal units. With the simultaneously reduced current supply, the output of the transmission line is increased. The quality of the transmitted signals is thus greatly enhanced.

The invention will be described hereinafter in more detail, by way of example, with reference to the drawings in which:

FIG. 1 illustrates a switching arrangement of the present invention with a transformer whose primary winding is interconnected with a transmitting unit;

FIG. 2 illustrates a switching arrangement of the present invention with two primary-sided auxiliary windings; and

FIG. 3 illustrates a transmitting unit with a device for the automatic tuning of a resonating unit.

FIG. 1 shows a transmitting unit TR, which is coupled to a coupling unit, that is the primary windings of a transformer TF1, to transmission Line UL, which forms the secondary winding of transformer TF1. This secondary winding normally includes only one winding. Transmission unit TR, which gives off a modulated high frequency signal, comprises, for example, a preamplifier and a final amplifier. The main inductivity resulting from the described details requires very high current, which via the generally utilized supply sources, particularly supply sources powered by batteries, cannot be extracted or not extracted for an extended period of time. This problem is solved via the hereinafter described utilization, as per this invention, of a passive current amplifier. The switching in of one or more capacitors C1, . . . , Cn, via switch S1, . . . , Sn, onto winding W1 forms a parallel resonance circuit, which can be tuned to a high and/or carrier frequency. The tuned resonance circuit acts in this manner as a pure resistance Rp. The current, which conforms to the quotient of voltage Ur and the effective resistance Rp achieves the minimum value at resonance. In the reactive impedance, at that time, resonance streams Ir are pulsating which achieve much higher values than the current I flowing in from the outside. Thus, with lesser power supplied from the outside, greater currents can be induced in the secondary windings. Of course, tuneable capacitors (variable capacitors Cd, capacitance diodes Cv, etc.) can also be advantageously utilized.

In FIG. 2, transmitting unit TR is connected with a first spool, respectively, winding W1 of a transformer TF2. Via the use of spools, respectively windings W2, W3 of transformer TF2 and capacitors C1, . . . , Cn, a tuneable parallel resonance circuit is formed on the primary side which is coupled in a transformer-type manner to winding W1. Capacitors C1, . . . , Cn can be switched on upon demand. Winding W3 is provided for switching same, via switch Sw, onto winding W2 so that the resistance circuit is tuneable over a wider region. In this manner it can also be provided that winding W2 or winding W3 can singly, or that windings W2, W3, serially switched together, can be switched onto capacitors C1, . . . , Cn.

FIG. 3 shows a switching arrangement according to the present invention in which the parallel resonance circuit is automatically tuneable. The principal item of the switching unit is tuning unit T via which the capacitors C1, . . . , Cn and the windings W3 and/or W2 are thusly always switched on so that the resonance frequency of the resistance circuit continuously changes, until the switching unit takes notice that the carrier frequency is close enough to the carrier frequency of the sending signal. It has been found to be advantageous to maintain the current I, outgoing from transmitting unit TR to winding W1, and to modulate the resonance circuit, until current I is minimal or below a predetermined threshold value. The minimal value of current I, as per the previous explanation, always occurs when, at the sending unit, only the relatively high resistance Rp of the measurement circuit occurs. The minimal value of current I thus only occurs in the case of resonance. The illustrated switching arrangement is comprised of a bistable or flip flop toggle stage BST-KS whose outlet is connected with the inputs of a clock generator C and a counter Z, which are contained in tuning unit T. Transmitting unit TR is connected, via a resistance Ran, with winding W1 and the input of a rectifier stage RECT, whose output and a line REF, which includes a voltage threshold, are each connected with the input of a comparator COMP. The output of comparator COMP, as well as a signal and command line S&IO, connected to a non-illustrated control unit, each are also connected with the input of flip flop toggle stage BST-KS. The output of flip flop toggle stage BST-KS is additionally connected, via a monostable toggle stage MST-KS, with a control unit, respectively via line S&IO, via which the signals of the transmitting unit TR that are to be transmitted, are channelled thereto.

The switching arrangement of FIG. 3 functions as follows: A start signal for the tuning procedure is channelled to the flip flop toggle stage BST-KS via line S&IO, whereinafter clock generator C and counter Z, connected with toggle stage BST-KS, are activated. Counter Z, which receives timing signals from clock generator C, begins the counting procedure from an existing or freely chosen count of the counter. Counter Z can be a simple dual counter whose outlets switch, via switcher So, . . . , Sn, respectively Sw, capacitors C1, . . . , Cn or windings W3 and/or winding W2, onto the resonance circuit. Switches SO, . . . , Sn, respectively Sw, are, for example, activated via switching transistors. The capacitors C1, . . . , Cn and windings W are chosen corresponding to the value of the counter outputs, so that a uniform tuning procedure is achieved. Transmitting unit TR outputs, during the tuning procedure, a signal, having the desired carrier frequency, to winding W1. Via resistance Rm a voltage, proportional to current I, is tapped and channelled to the input of rectifier Stage RECT, which in turn channels a corresponding DC voltage to the input of comparator stage COMP. In case this voltage, close to resonance, is smaller than the voltage threshold delivered to comparator stage COMP, via line REF, a signal is sent to flip flop toggle stage BST-KS, whereafter the same is set back. Via the setback of flip flop toggle stage BST-KS, clock generator C and counter Z are stopped, so that the current count of the counter is retained. In addition, monostable toggle stage MST-KS is activated, which reports back the successful conclusion of the tuning procedure to the control unit, via lead S&IO. In order to reduce the number of connecting leads, the sending signal and the command signal are carried on only a single line. The signals are channelled to toggle stage BST-KS preferably via a Schmitt trigger, which transforms the incoming signal into a clean square wave signal. In the interest of simplicity, of course separate command leads can be used, which are separated from the sending signal leads. Preferably, counter Z is connectable with a D/A converter, which outputs a voltage, proportional to the count of the counter, to a variable capacitor Cd, Cv.

In addition, for uses in the telephone field, normally a tuning arrangement is utilized not only for the voice channel but also for the signal channel. Generally, only a single frequency is assigned to the signal channel. In contrast thereto, the voice channel utilizes several carrier frequencies, which can be dispersed over a wide frequency region. This means that the resonance circuit of the voice channel must be tuneable over a wider region, which can be achieved through the potential switching on of windings W3 and/or W2. The signal channel and the voice channel therein include a switching arrangement which, in principle, corresponds to the arrangement shown in FIG. 3. Clock generator C can be jointly utilized for both channels, or switched on via an OR-gate. Also, the acknowledgement pertaining to the termination of the tuning procedure of the signal or voice channels can be accomplished via a joint line.

In addition, the tuning arrangement could be constructed with the aid of a microprocessor. Therewith however, a greater capacity would be required.

In case the transmitter is switched off upon the termination of a conversation, the count of the counter is retained. In addition, when, in place of transmitting unit TR, a substitute resistance is switched onto winding W1, the impedance ratios in transmission line UL remain constant.