DE1958755C3 - Threshold switch with a response threshold that can be controlled depending on the amplitude of the input signals - Google Patents

Description

When information is transmitted by means of pulses with a uniform amplitude, this is known to result the advantage that the useful signals can be separated from interfering signals in a simple manner. This separation is usually done by a threshold switch that only emits a signal when the input signal has exceeded a certain value, the threshold.

It is also known that instead of rectangular pulses, pulses in the form of a sine half-wave are advantageously given to the transmission path, since these contain much fewer harmonics than other shaped pulses, especially rectangular ones, which thereby crosstalk to other lines and in cause these interfering signals. The original square-wave signal must be restored in the receiving devices in the end points and generally also in the intermediate points, usually called regenerative amplifiers in the case of pulse transmission links. The threshold switch, which quickly delivers a powerful output signal after the threshold is exceeded, also fulfills this task.

Finally, it is known that when transmitting a Consequence of unipolar impulses the cores of transformers in the course of the transmission line in disadvantageous Way to be premagnetized. This is avoided in that two consecutive pulses be transmitted with opposite polarity. The pulse train transmitted in this way is called pseudo or Quasiternary designation Here too, must be used in the receiving devices the original unipolar pulse tolge, either through a separate full wave rectifier or advantageously again by a rectifying threshold switch that is required anyway getting produced.

Those from the transmitting facilities onto the transmission line given pseudo-ternary pulse train gets distorted by unavoidable conduction properties and strongly attenuated to the receiving device. A first, approximate equalization of the received Pulse train is effected by an equalizer immediately after the input of the regenerative amplifier. The completely equalized and on their original Value-amplified pulse train is only available at the output of the regenerative amplifier. To the Input of the threshold switch connected downstream of the equalizer a pre-equalized, damped pulse train is thus supplied. Due to the particular dependency Cable attenuation that fluctuates with temperature also changes the amplitude of the received Impulses.

The separation of even larger interfering signals from the useful signals requires the highest possible threshold the threshold switch, the reliable detection of the useful signals by the threshold switch an amplitude the useful signals at a greater distance above the threshold voltage. A Considered threshold voltage of about half the value of the amplitude of the received pulses. From it it follows that it is advantageous in view of the fluctuating magnitude of the amplitude of the received pulses is to control the Schwellenspanriung of the threshold switch as a function of this and thus to achieve an optimal effect.

A circuit according to the preamble of claim 1 is known from "The Bell System Technical Journal, January 1962, pp. 51,52; 22 and 23 «. there describes a threshold switch in which the bases of two transistors that can be driven in phase opposition can be controlled via a transistor and a transformer and from an output signal at an output transformer is removed. Through the control in the high-resistance base circuits and through the considerable load on the circuits by the inductances of the transformers is a proper one Separation of the useful signals from the interference signals

difficult and the transmission quality of the switching edges is significantly reduced.

Accordingly, the object of the present invention is to design a threshold switch according to the preamble of claim 1 in such a way that the useful signals are cleanly separated from the interfering signals and at the same time are not excessively distorted by the pulse currents of the useful signal.
The arrangement for solving this problem is in

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i claim 1 described.

\ Advantageous embodiments are shown in the sub-I sayings

[The invention is illustrated below with the aid of a simplified circuit diagram F i g. 1 and an exemplary detailed circuit diagram F i g. 2 explained in more detail
IF i g. 1 shows the actual rectifying I threshold, consisting of a grounded to the I center tap its secondary winding Eih- \ gangs differential transformer Tr, two transistors \ Ts 1 and Ts 2, whose bases are respectively connected to one end of: the secondary winding of the transformer, whose collector ; gates are connected in parallel and have a common. Men coil resistor Ri with one pole of the supply voltage and its emitter connected in parallel; and are on a common Emittervorwider- \ R 2 mil was the second pole of the supply voltage ■ are connected. As far as described so far, the I arrangement forms a Vcüwegrectifier with active ^; Rectifier elements, whereby these firstly receive an increased, constant response threshold due to the voltage drop at the common emitter resistor "and Ä2, and secondly with a sufficiently large: Emitter series resistor R 2 work like a differential amplifier, with one of the transistors"! TiI or Ts 2 the blocking effect of the respective other transistor is increased.

An oscillation of any shape fed to the primary winding of the transformer via the input £ causes a unipolar signal that can be picked up at the parallel-connected collectors of the transistors at output A whenever the threshold voltages of one of the two transistors Ts 1 or Ts 2 are exceeded.

It is known in differential amplifier circuits to replace the common emitter series resistor with a transistor circuit that keeps the sum of the emitter currents of the two transistors constant. In the threshold switch according to the invention with a response threshold that can be controlled as a function of the amplitude of the input signals, a transistor circuit with the transistor Ts3 is also used in the common emitter circuit of the two rectifying transistors TsI and Ts 2, but this does not have the task of calculating the sum of the emitter currents of the two rectifying transistors TsI and to keep Ts 2 constant, but which in turn changes the response threshold of the two rectifying transistors in proportion to the amplitude of the input signals, controlled by the size of the input signals of the threshold switch. The control variable for the transistor Ts 3 is obtained from the input signal by a full wave peak rectifier Gr , the input of which is expediently connected to the ends of the secondary winding of the transformer Tr and the output of which leads to the base of the control transistor Ts 3. By means of a voltage divider at the output of the peak rectifier Gr , the response threshold of the threshold switch can be set to a desired proportion of the amplitude of the input signals.

In the exemplary detailed flow diagram F i g. 2 corresponds to the actual threshold switch with the transformer Tr, the transistors TsI, Ts 2 and Ts3 and the resistors R 1 and R 2 in connection with F i g. 1 described. The peak value rectifier consists essentially of the transistors Ts 4 and Ts 5 connected with their bases to one end of the secondary winding of the transformer Tr , the collectors of which are connected in parallel to one pole of the storage tank.

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65 sesvoltage and its emitter are connected in parallel via a common emitter resistor R 3, RA at the second pole of the supply voltage, and a charging capacitor G whose first layer is connected via a protective resistor R 5 to the parallel-connected emitters of the transistors Ts4, Ts5 and whose second layer is grounded .

Parallel to a larger part A4 of the common emitter series resistor A3, R4 of the transistors Ts4, Ts5 is the collector-emitter path of a switching transistor Ts 6, which can be conductively controlled by the input signals of the threshold switch via the full-wave rectifier diodes Dt, D 2 and a base voltage divider .

The high-resistance input of a two-stage amplifier acting as an impedance converter with the mutually complementary transistors Ts7 and Ts8 lies parallel to the charging capacitor C. The control signal for the control transistor Ts3 can be picked up at the tap of a voltage divider R6, Rl in the emitter circuit dr · - output transistor Ts 8 of the amplifier.

The complete circuit arrangement for obtaining the control voltage for the control transistor Ts3 works in the manner described below:

It is assumed that the charging capacitor C has an average charging voltage from a previous charge. With each input signal E of any polarity, the switching transistor Ts 6 is turned on, since its threshold voltage and the threshold voltage of one of the diodes Di or D 2 are fully compensated by the diodes D 3 and D 4. If the amplitude of the input signal is less than the sum of the charging voltage of the capacitor C and the threshold voltage of one of the transistors Ts 4 and Ts 5, then these two transistors remain blocked and the capacitor C is via the resistors /? 5 and /? 3 and the Discharge coil-emitter path of transistor Ts6. The capacitor CAIS Speisespannungsquellc for the transistor Ts is then used 6. Where the drop in the charge voltage of the capacitor C the value of the decreased by the threshold voltage of the transistors Ts4, Ts5 voltage of the input signal, so starts depending on the polarity of the input signal, either transistor Ts4 or Hiten transistor Ts5 and a current now flows from the supply voltage source + U via one of the transistors Ts 4 or Ts 5, the resistor Λ 3 and the transistor Ts 6 to - U. The voltage on the capacitor C is equal to the threshold voltage of the transistors Ts4 or Ts5 reduced amplitude voltage of the input signal is retained and drops only slightly even after the end of the input signal until the occurrence of the next input signal, since when the transistor Ts 6 is blocked, there is a high resistance value of the series connection of resistors Λ3, A4, R5 and a high input resistance of the amplifier Ts 7, Ts 8 the time constant of the arrangement is large. If, on the other hand, the amplitude of the input signal is greater than the sum of the charging voltage of the capacitor C and the threshold voltage of one of the transistors Ts 4 or Ti5, and this will also be the case because of the slight discharge of the capacitor C in the meantime, if the amplitude of the input signal is the same is as large as the amplitude of the previous signal, depending on the polarity of the input signal, either the transistor Ts4 or the transistor Ts5 conducts, a current flows from the supply voltage source + U via the conductive transistor Ts 4 or Ts 5 and the protective

resistance R 5 and charges the capacitor C to the voltage of the amplitude of the input signal reduced by the threshold voltage of the conductive transistor. As the charging voltage of the capacitor C increases , the conductive transistor Ts 4 or Ts 5 becomes highly resistive and blocks when the charging voltage has reached the value of the input voltage minus the threshold voltage. The value of the protective resistor R 5 is small, as is the resistance value of the conductive transistor 7s4 or Ts5 during charging, so that the capacitor C is charged quickly with a small time constant. In contrast, the resistance R 3 is comparatively large, so that, despite the switching transistor 756 which is simultaneously conductive, the charge of the capacitor C is not adversely affected.

In the impedance converting its input parallel with the charging capacitor Cliegenden amplifier Clic SciiwciicfiS kuiiipciiiici'i | Jäi.Müng UCS ciSicfi Tfäfisi stors TsI, the threshold voltage of the conducting transistor Ts4 or Ts 5 of the peak voltage of the rectifier and the diode D 5 between the emitter of the first transistor Ts 7 and the base of the second transistor TsS the threshold voltage of the second transistor TsS, so that the voltage at the emitter of the transistor TsS corresponds in each case to the peak value of the last input signal. The part of this voltage which is fixed by the tap between the resistors RS and R7 forming the emitter series resistor of the transistor Ts 8 determines the respective threshold voltage of the threshold value switch. so

The load on the input and thus attenuation of the input signals by the peak value rectifier connected in parallel to the input is low, since the base voltage divider of the switching transistor Ts6 has a high resistance, and because the respective conductive transistor a TsA or TsS of the actual peak value rectifier only has a gain factor equal to the current smaller value of the charging current of the capacitor CbelasteL

The circuit arrangement has the advantages that it does not have to be adjusted and that it is fully temperature compensated isL

1 sheet of drawings

Claims (3)

Patent claims: 1. Threshold switch with a response threshold that can be controlled as a function of the amplitude of bipolar input signals, in particular for separating the useful signals from interference signals in regenerative amplifiers in pulse transmission paths, in which the actual threshold switch consists of two transistors that can be controlled in phase opposition via their base by the input signals, the emitters of which are connected to one of the Response threshold of the threshold switch controlling transistor, which in turn is controlled by a DC voltage obtained from the input signals by peak rectification and which is proportional to the respective amplitude of the input signals, characterized in that the transistor (Ts 3) controlling the response threshold is connected to the common transmitter lead of the two transistors (Ts 1 , Ts 2 $ of the threshold switch is switched on and that the collectors of these two transistors (Ts i, Ts 2) are connected to a common ohmic collector resistor (R 1) are old at which the output signal can be removed. 2. Threshold switch according to claim 1, characterized in that the transistor controlling the Aiissprechschwelle is in turn controlled from two transistors (TsA, TsS) serving as rectifiers whose collectors and the emitter are connected in parallel, each of which is connected in parallel via their base by the input signals controllable in antiphase by the input signals Charging capacitor (C) lying parallel to the common Emktervo, resistor (R 3, R 4) of the transistors (Ts 4, Tr-S ) and a DC amplifier (Ts 7, Ts 8) with its high-resistance input parallel to the charging capacitor and serving as an impedance converter ) at the low-resistance output of which the control voltage for the control transistor (Ts 3) can be removed. 3. Threshold switch according to claim 2, characterized in that the larger part (R 4) of the common emitter series resistor (R 3, A4-} of the transistors serving as rectifiers (Ts4, TsS) is the collector-emitter path of a switching transistor ( 7i 6) is connected in parallel.