DE2339806A1 - CARRIER FREQUENCY TRANSMISSION OF DIGITAL SIGNALS - Google Patents

Description

SIEMENS AKTIENGESELLSCHAFT Munich, - AUG 6. 1373

Berlin and Munich Wittelsbacherplatz 2

VPA 73/6640

Carrier-frequency transmission of digital signals, addition to VPA 73/6570 (current number: P 23 18 800 ^ 3-31)

The main patent relates to a communication system for a carrier-frequency transmission of analog signals with two end points, which are optionally interrupted by multiple pairs of symmetrical or coaxial ones Cables are connected. The communication system according to the main patent is constructed so that for at least one two-wire connection a source for digital, in particular pulse-code-modulated signals is provided in the transmitting part of the terminals, that in the intermediate points either a regenerator or a line amplifier is provided that in the receiving part of the Terminals a regenerator is provided that every source in the terminals and every regenerator in the intermediate points a modulator is connected downstream in which the digital signals are converted into their frequency position by means of carrier-frequency conversion be shifted so that each modulator has a frequency filter it is connected downstream that a demodulator is provided in the receiving section of each terminal and in each intermediate point with a regenerator is in which the digital signals are recovered and that a pair of lines of the cable for the transmission of the Carrier-frequency converted digital signals is provided.

It is useful in the end points and in the intermediate points provided with regenerators frequency multipliers and / or frequency dividers, which from the bit rate of the Derive digital signal carrier frequencies, which on the transmission side convert the digital signal by half the bit

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repetition frequency and a corresponding one on the receiving side Effect reversal.

In the communication system according to the main patent, it is "possible via a carrier frequency connection to transmit analog and digital signals in parallel. It comes to a mutual influence, which especially with the analog signal and there in an increase in the side-by-side speech * due to crosstalk of the digital signal expresses. There is therefore a demand for the lowest possible level for the digital signal.

Since the main energy of a random bit sequence of the digital signal lies in the lower frequency range, becomes special a level reduction is required for this frequency range. This is countered by the cable attenuation, which increases with the frequency, so that a compromise was found for shifting the digital signal to be transmitted to higher frequencies must become.

According to a particularly favorable embodiment of the main patent, the digital signal is therefore converted on the sending side by half the bit rate and on the receiving side a corresponding reverse conversion. In the implementation There are a number of considerations to keep in mind on the sending side. Will be implemented in a single step made by modulation with the aid of a carrier of the appropriate frequency, then the modulated output signal appears partly in the same frequency range as the digital signal to be modulated at the input, so that the two signals are separated is not possible and therefore both signals appear on the output side.

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It is therefore usually a double conversion, i.e. the successive modulation with two carriers different frequency made. The modulation with the first relatively high-frequency carrier creates in sufficient frequency spacing from the original band two high-frequency sidebands, one of which with the help of one Bandpass is screened out. By modulating this sifted out sideband with an adjacent one in terms of frequency Carriers of a slightly higher frequency result, along with other modulation products, in a relatively low-frequency signal band in the desired frequency range. It can be seen that the double conversion described requires considerable effort.

The invention is therefore based on the object, the effort when converting the digital signal. When solving the task, it must also be taken into account that the modulated digital signal should be directly regenerable on the transmission link and that, for example, a pseudo-ternary coded signal should be available again in pseudo-ternary coded form after the modulation. this happens taking into account the energy distribution in pseudo-ternary coded signals through which the transmission of digital signals in pseudo-ternary coded form is particularly advantageous.

The object is achieved according to the invention by a method for modulation in which a rectangular pulse train is used as the carrier with half the bit rate is derived from the bit rate of the digital signal and the zero crossings the pulses of the digital signal and the carrier are shifted by 90 ° against each other. The advantage of this procedure is that the conversion of the digital signal into the desired frequency range by a single modulation with a single carrier using the digital character of the signal to be converted takes place.

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According to a particularly favorable special variant of the method according to the invention. Claim 1 results from that the digital signal to be modulated and that in the form of a sequence of square-wave pulses with positive or negative Amplitude present carriers are linked so that when the digital signal disappears independently the carrier amplitude does not emit any output variable that is independent of the amplitude when the carrier is no longer available of the digital signal no output variable is emitted that with a positive amplitude of the digital. Signal and more positive Amplitude of the carrier a positive amplitude value is given as the output variable,

that in the case of a negative amplitude of the digital signal and a positive amplitude of the carrier, a negative amplitude value is output as an output variable, that in the case of a positive amplitude of the digital signal and a negative amplitude of the carrier, a negative amplitude value is output as an output variable and that in the case of a negative amplitude of the digital signal and a negative amplitude of the carrier, a positive amplitude value is emitted as the output signal.

Because of its simplicity and clarity, this method has a number of advantages; it can be when using voltage variables as signal variables, it is particularly advantageous with the aid of the known digital ones Perform circuit arrangements.

A particularly simple and easy to implement digital circuit arrangement for implementing the above The method consists in a modulator which is constructed in the manner of a digital double push-pull modulator and a first pair of input terminals for the digital signal, a second pair of input terminals for the carrier, four NAND

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Gates, two AND gates, an output transformer and two signal outputs and in which the first input of the first gate is connected to the first input for the digital signal, the second input of the first gate is connected to the first input for the carrier, in which the first input of the second gate with the second Input for the digital signal is connected and the second input of the second gate with the second input for the carrier is connected, in which the first input of the third gate with the second input for the carrier and the second input of the third gate is connected to the first input for the digital signal, in which the first input of the fourth gate with the first input for the carrier and the second input of the fourth Gate is connected to the second input of the digital signal,

in which the output of the first NAND gate is connected to the first input of the first AND gate, in which the output of the second NAND gate is connected to the second input of the first AND gate, in which the output of the third NAND gate is connected to the first input of the second AND gate, in which the output of the fourth NAND gate is connected to the second input of the second AND gate, in which the outputs of the first and the second AND gate each with a connection of the primary winding of the output transformer are connected,

in which the outputs for the output signal are each connected to a connection for the secondary winding of the output transformer and
in which connections for the power supply are provided.

The invention will be explained in more detail below on the basis of exemplary embodiments shown in the drawing will.

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It shows.

1 shows the schematic representation of a message transmission system according to the main patent,

2 shows the voltage curves of the digital to be modulated Input signal, the carrier and the modulated output signal,

3 shows the spectral distribution for the pseudo-ternary coded signal of a random sequence before and after Modulation,

4 shows the schematic representation of a digital double push-pull modulator according to the invention and

5 shows the circuit of a digital double push-pull modulator according to the invention.

Fig. 1 shows a terminal I, intermediate points II and III and a further terminal IV of the communication system according to the main patent. The terminals and the intermediate points contain a number of elements, whereby for the sake of clarity only the elements are shown which are necessary for the transmission of messages from the terminal I to the terminal IV.

The terminal Γ contains a source 1, a modulator 5 »a frequency filter for the transmission of digital signals 7 and a frequency divider and / or frequency multiplier 12. For the transmission of carrier-frequency analog signals the terminal I contains a source 13.

The intermediate point II contains a demodulator 9 »a regenerator 2, a for the transmission of digital signals Modulator 6, a frequency filter 8 and a frequency divider and / or frequency multiplier 13. For the transmission The intermediate point II contains the carrier-frequency analog signals

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an amplifier 14.

The intermediate point III contains an amplifier 12 for the carrier-frequency transmission of analog signals and a line amplifier 3 for the carrier-frequency transmission of digital signals in each case a two-wire line.

Are the amplifier or regenerator distances for Transmission of the converted digital signal smaller than the required amplifier spacing for the transmission of the Carrier-frequency analog signal, then contain the intermediate point II and III instead of the amplifier 14 and 12, respectively Frequency filter to avoid feedback caused by crosstalk between the two-wire lines from the output to the input of the digital cable run.

The terminal IV contains a demodulator, a regenerator 4 and a frequency divider and multiplier 14 for the reception of the digital signals. The terminal IV also contains a receiver 15 for carrier-frequency analog signals,

The terminal I is via the intermediate points II and III with the terminal IV is connected by multi-pair transmission pairs 11. The message transmission in the message transmission system according to the main patent, the procedure is that the digital signals are transmitted from source 1, which are shifted in their frequency position in the modulator 5 by a carrier-frequency conversion. The necessary for this The carrier frequency or the necessary carrier frequencies are determined by means of the frequency multiplier and / or frequency divider 12 derived from the bit rate of the digital signals.

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The output signals of the modulator 5 are transmitted via the frequency filter 7 and a two-wire line of the cable 11 in the intermediate point II the demodulator 9 at the same time with the over the frequency multiplier and frequency divider 13 derived from the bit rate of the digital signal carrier frequencies. The recovered The digital signal is regenerated in the regenerator 2 and then in the modulator 6 to the frequency multiplier and frequency divider 13 modulated carrier obtained. The output signal of the modulator 6 is via the Frequency filter 8 and a two-wire line of the transmission cable 11 of the intermediate point III. After the reinforcement In the line amplifier 3, the signal arrives at the same time via a two-wire line of the cable 11 in the terminal IV with that obtained by the frequency multiplier and frequency divider 14 from the bit sequence of the digital signal Carrier frequencies to the demodulator 10 and via this to the regenerator 4, from which it can be taken. The following Explanations relate mainly to a further development of the modulation method and to appropriately trained ones Modulators that are used in the communication system described as modulators 5, 6 in the terminal I and the Intermediate point II can be used.

In Fig. 2, the phase relationships between the to mo- " Dulating digital input signal E1, the carrier E2 and the modulated digital output signal P shown. It it can be seen that the digital input signal E1 to be modulated and the modulated output signal P can assume the amplitude values +1, 0, -1 and are coded in pseudo-ternary fashion Form present, while the carrier E2 is a rectangular pulse train, the amplitude of which Can assume values +1 and -1.

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Fig. 3 consists of two parts, the first part is the spectral distribution of a pseudo-ternary coded digital Input signal and in the second part the spectral distribution of the also pseudo-ternary coded and in the higher frequency position converted output signal shown. In both cases the solid line shows the voltage level, that is, the energy distribution of a random sequence as a function of the normalized frequency; also are marks a series of periodic sequences, of which the sequence denoted by χ is particularly noteworthy, which describes the signal during the pause in speech. The comparison shows that the area is maximum Level and thus maximum energy was shifted to higher frequencies by the modulation, so that the The area of maximum crosstalk has been moved to higher frequencies. This is especially true for the additional depicted periodic sequences, which are often neglected in such considerations, although they are based on Due to their high level, they are often particularly annoying.

4 shows the schematic representation of a digital double push-pull modulator according to the invention with a first pair of input terminals 21, 22 for the first input variable E1, a second pair of terminals 23 »24 for the second input variable E2 and an output terminal pair 25, 26 for the output variable P. Leads such a circuit according to the method according to the invention, the voltage of a _{signal encoded in a pseudo-ternary code (AM ^ HDB n} , CHDB _n , B6ZS) with full-bit-wide square-wave pulses as input variable E1 and, at the same time, a square-wave clock signal voltage with a clock ratio of 1: 2 as input variable E2 and half the bit rate of the pseudo-ternary signal, the output variable P is the voltage of a signal that is also pseudo-ternary

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- ίο _

is coded. According to the method according to the invention, the zero crossings of the pulses of the to be modulated Input signal E1 and the carrier E2, shifted against each other by half a bit width, then each zero crossing of the square-wave pulse train of the carrier E2 lies in the middle of time two zero crossings of E1. The level of the pseudo-ternary coded and modulated output signal is thus P at frequency 0, i.e. with direct current, the same as that of the input signal to be modulated, i.e. also the same 0.

5 shows the design of a digital double push-pull modulator according to the invention, which consists of 4 NAND gates, 2 AND gates, 4 input terminals 21, 22, 23, 24, an output transformer and interconnections. In a thus constructed digital double-balanced modulator, it is expedient that incoming pseudoternär encoded input signal E1 'split, wherein E1' initially in two unipolar pulse trains E1'und E ¹ includes only the positive and E1 ^'f only the negative pulses of the input signal. The pulse train E1 'is supplied to the input terminal 21 and the pulse train E1' ^{f is} supplied to the input terminal 22.

From the rectangular clock signal of the input variable E2 an inverted square-wave clock signal is derived, the input terminal 23 being the original square-wave Clock signal and the input terminal 24, the inverted square-wave clock signal are fed. Of the Both input terminal pairs are the signals to the inputs of the 4 NAND gates. supplied namely the signals the first input terminal 21 each have an input 71, 92 of the first and third NAND gates 27, 29; the signals

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the second input terminal 22 each to an input 81, 102 of the second and fourth NAND gates 29, 30, 'the signals of the third input terminal 23 to the other input 72, 101 of the first and fourth NAND gates 27, 30 and the signals of the fourth input terminal 24 to the other input 82, 91 of the second and third NAND gates 28, 29. According to the known function of the NAND gates, the supplied signals are linked and are available in linked form at the outputs of the respective NAND gates . The signals from the output of the first NAND gate 27 then ground to one input 111 of the first AND gate 81, the signals from the second NAND gate 28 to the second input 112 of the first AND gate, and the signals from the third NAND gate the first input 121 of a second AND gate and the signals of the fourth NAND gate are fed to the second input 122 of the second AND gate. Corresponding to the known link in the AND gates, new output signals arise which are each fed to a connection of the primary winding of an output transformer from the output of the two AND gates. The secondary winding of the output transformer is connected to one of the two output terminals 25 _f 26, from which the output signal can be tapped in symmetrical form. The output transformer can be replaced in the usual way by known push-pull circuits. In the present case, the power supply to the digital logic elements is provided via a center tap, not shown here, of the primary winding of the output transformer.

The output terminals can be used to further reduce the low-frequency components of the modulated output signal in particular of the digital double push-pull demodulator according to the invention with a bandpass filter, the pass band between

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the normalized frequencies Ω = 0.5 and Ω = 1.5. The modulated digital one is obtained in this way Output signal in analog form that corresponds to the main patent of the other parts of the communication system is fed.

5 figures

4 claims

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Claims (4)

Claims. •1.! A method for modulating a digital, in particular a pulse code modulated and pseudoternär encoded signal in a communication system for a carrier-frequency transmission of analog signals having two terminals which, by optionally interrupted by Zwischehstellen multipair symmetrical or ^coaxial: cables are connected and in which the modulation following each the sources takes place in the transmission part of the terminals and after each of the regenerators in the intermediate points and in which the carrier frequencies are derived from the bit rate of the digital signals according to claim 2 of patent (P 2 318 800.3-31), characterized in that a rectangular pulse train with half as a carrier Bit rate is derived from the bit rate of the digital signal and the zero crossings of the pulses of the digital signal and the carrier are shifted by 90 ° against each other. 2. The method for modulation according to claim 1, characterized in that that to be modulated digital signal and a sequence of rectangular pulses with positive or negative amplitude present in the form of supports are linked so that no output is delivered in case of failure of the digital signal regardless of the carrier amplitude, that with omission of the support independent of the amplitude of the digital signal no output variable is given, that with a positive amplitude of the digital signal and a positive amplitude of the carrier a positive amplitude value is given as an output variable, VPA 9/640/3016 a - 14 - 509809/0433 that with negative amplitude of the digital signal and positive amplitude of the carrier a negative amplitude value is given as output variable, that in the case of a positive amplitude of the digital signal and a negative amplitude of the carrier, a negative amplitude value is output as an output variable and that in the case of a negative amplitude of the digital signal and a negative amplitude of the carrier, a positive amplitude value is emitted as the output signal. 3. A method for modulation according to claim 2, characterized marked, that the signal quantities are voltage quantities. 4. modulator for performing a method according to claim 3, characterized in that a digital double push-pull modulator is provided which has a first pair of input terminals (21, 22) for the digital signal, a second pair of input terminals (23 _f 24) for the carrier, four NAND gates (27, 28, 29, 30), contains two AND * gates (31, 32), an output transformer (33) and two signal outputs (35, 36) and in which the first input (71) of the first gate (27) is connected to the first input for the digital signal (21 ) is connected, the second input (72) of the first gate (27) is connected to the first input (23) for the carrier, in which the first input (81) of the second gate (28) is connected to the second input (22) for the digital signal and the second input (82) of the second gate (28) is connected to the second input (24) for the carrier, in which the first input (91) of the third gate (29) with • the second input (24) for the carrier and the second VPA 9/640/3016 a - 15 - 509809/0433 Input (92) of the third gate (29) is connected to the first input (21) for the digital signal, in which the first input (101) of the fourth gate (30) with the first input (23) for the carrier and the second input (102) of the fourth gate (30) is connected to the second input (22) of the digital signal, at. which the output of the first NAND gate (27) with the first input (111) of the first MD gate (31) connected is, in which .the output of the second NAND gate (28) with the second input (112) of the first AND gate (31) is connected, in which the output of the third NAND gate (29) with the first input (121) of the second AND gate (32) is connected, in which the output of the fourth gate (30) with the second input (122) of the second AND gate (32) is connected, in which the outputs of the first and second AND gates (31, 32) each with a connection of the primary winding of the Output transformer (33) are connected, in which the outputs (25, 26) for the output signal, respectively are connected to a terminal for the secondary winding of the output transformer (33) and in which connections for the power supply are provided. VPA 9/640/3016 a 509809/0433 Blank page