RU2132113C1 - Commutator for switching calling voltage off in electronic user's circuit - Google Patents

Abstract

FIELD: telephone equipment. SUBSTANCE: electronic user's circuits have sensitive circuits for current recognition (S) which control current (I) in user's line. User's call is modeled by repeated interruption of alternating calling voltage which induces alternating current in user's line. However, call alternating voltage are switched in proximity of zero level transition. In switching phase, there exists danger of generation and running of current which is caused by capacitance load of connected user's circuit, which causes user's line current leading to false line recognition. Goal of invention is achieved by comparator (K2) using very low comparison voltage (Uv) by means of switching call current in close proximity of zero level transition after detection of user's line current (I) using current recognition circuit (S). EFFECT: elimination of false recognition of user's line. 1 dwg

Description

 The invention relates to a switching device for disconnecting ring voltage in an electronic subscriber circuit, which forms a pairing device between the subscriber line and the telephone system. The beginning and end of telephone communication are signaled by closing and opening the electric circuit; in telephone sets with pulse dialing, the electric circuit is interrupted rhythmically during the dialing process. Changes in the magnitude of the current in the subscriber branch are set by the detector circuit, the process is referred to as identification of the branch. The desired telephone connection is signaled by an alternating call voltage, which is interrupted with a certain rhythm. The presence of an alternating call voltage on a telephone line is called a call phase.

 It is generally known that the connection and disconnection of alternating voltage of a call are made near the transitions through a zero value in order to avoid the occurrence of interfering voltages on subscriber lines and, if possible, errors when recognizing a branch, as well as to keep the load of the corresponding elements to a minimum level by switching on only low currents.

 The switching on and off process specifically for the branch identification procedure during the call phase has already been described, see, for example, DE 3231573 A1. If the called subscriber does not answer, that is, the process of recognizing the branch does not take place, then in accordance with the call cycle after a certain time during normal operation, when the transition through the zero value of the alternating voltage of the call, the subscriber circuit is switched on. During the called phase, a low-pass filter with a time constant τ = 50 - 80 ms must be turned on before the branch identification circuit in order to sufficiently extinguish the alternating call current superimposed on the recognizable direct current. In normal use, this time constant disappears, because otherwise the process of branch identification would be unacceptably slow. In the absence of a call command, the low-pass filter is turned off through a logic signal so that during normal operation, each current change in the subscriber branch will be recognized without delay. However, this raises the problem of disconnecting the call voltage. If the disconnection of the AC voltage of the call occurs near the transition of this voltage to zero, then there is a danger that as a result of the phase shift between the voltage and the current due to the capacitive load of the connected subscriber circuit, a current will flow, which will simulate the branch current and lead to erroneous recognition of the branch, since the time constant τ = 50 - 80 ms in this case does not work.

 True, it is possible to make this erroneous subscriber behavior invalid due to additional costs in the software provided for branch recognition, however, the present invention seeks to eliminate the source of branch misidentification using a simple, easily integrable device.

 This task in accordance with the invention is solved using the switching device described in paragraph 1.

 The essence of the invention lies in the fact that using the comparator between the current recognition circuit and the logic of processing the results, a situation is reached in which the call current is disconnected immediately near the transition through the zero value of the branch current, so that practically during the disconnection phase the branch current cannot be simulated .

 The solution according to the invention is illustrated below by way of example. The attached drawing shows a diagram of a switching device according to the invention.

 In accordance with the drawing, the switching device consists of a current recognition circuit S with a low-pass filter TP and a first comparator K1 turned on and, in accordance with the invention, from a second comparator K2, a gate circuit G and a bistable circuit FF.

Using the current identification circuit S, the branch current I is taken, the signal is fed through the low-pass filter TP to the first comparator and compared with the reference voltage U _REF , for example, with U _REF ≈1B. If the output voltage of the low-pass filter TP is greater than the reference voltage, then a branch signal U _s is emitted from the first comparator K1.

In parallel to the circuit from the low-pass filter TP and the first comparator, a circuit from the second comparator K2, the gate circuit G and the bistable circuit FF is connected. The output RU 'of the bistable circuit FF is connected to a module that activates a call for the subscriber circuit. The second voltage comparator K2 compares the output voltage of the current recognition circuit S with a small bias voltage U _v , for example, with U _v ≈50 mV. If the output voltage of the current recognition circuit S is less than the bias voltage U _v , then the second comparator K2 controls the bistable circuit FF through the gate circuit. Using the logical call command RU, the low-pass filter TP, the gate circuit G and the bistable circuit FF are controlled.

 In the call phase, the logical call command RU conducts the signal High, that is, RU = H. With this command, the bistable circuit FF is activated, and RU '= H appears on its output. Using the High signal of the output of the bistable circuit FF, a subscriber call is activated. Together with the RU = H command, the low-pass filter time constant TP is activated. If the logical call command RU takes the Low-Pegel position, i.e. RU = L, then the low-pass filter time constant is turned off, and the path is prepared for the signal to pass through the gate circuit G. The second comparator K2 gives a signal only when the output voltage of the current recognition circuit S is less than the bias voltage, thus, almost only at transition through the zero value of the branch current. Then the output signal of the second comparator K2 passes through the gate circuit G to the bistable circuit FF and returns it to the initial value. Through the output RU '= L, the subscriber call is disconnected.

Claims (1)

 A switching device for disconnecting ring voltage in an electronic subscriber unit, comprising a current recognition unit with a low-pass filter connected in series and connected to a low-pass filter in series with a first comparator for recognizing a current in a branch and generating a branch signal, characterized in that the circuit is from a low-pass filter and the first comparator is connected to the circuit from the second comparator, valve block and bistable block in parallel from the input side, and to the second comparator a bias voltage is applied, which is a voltage slightly different from the zero potential, as a comparison voltage, while a logical call command is supplied to the low-pass filter, the valve block and the bistable block, and a logical signal is prepared at the output of the bistable block to enable or disable the subscriber call .