DE1212146B - Transmission system with pulse code modulated signals - Google Patents

Description

transmission system with pulse code modulated signals The invention refers to a system for transmitting signals in the form of pulse code modulation characters, which are sent in uninterrupted sequence with preferably high pulse repetition frequency in which, in addition to the message, there are also special synchronization characters for production the synchronization between the transmitting-side pulse code modulation device and the Evaluation of the pulse code modulation characters from the transmitter to the receiver on the receiver side be transmitted.

In the case of transmission systems working with pulse code modulation, the Message in a sequence of pulses of equal duration and amplitude according to a binary code implemented and converted back into the original form on the receiving side. On the transmitting and receiving sides, scanning devices must be provided which are synchronous constantly. That is, the two scanners must be both in frequency and coincide with each other in phase. The most popular type of synchronization in the case of pulse code modulation, the following is: A intended only for synchronization purposes Element of the code character is modulated on the transmit side in such a way that it falls below the receive side the signal elements remains recognizable. For example, this synchronous element always "0" or always "1" or alternating between "0" and "1". It can any chain code can also be used for identification. On the receiving side the synchronous elements are selected from the signal, thereby increasing the sampling frequency can be obtained according to frequency and phase position. With most known synchronization methods an element of the messaging code character is lost, and even if a sync pulse is not provided in each code character. If a synchro-character is added to every k-th code character, then results from this additional pulse both on the transmit side and on the receive side, in particular in the synchronization stage at the receiving end, a considerably greater effort.

The invention is based on the object of a system of the introductory type described especially with regard to the deficiencies and disadvantages described to improve significantly.

This task is performed in a system for the transmission of signals in In the form of pulse code modulation characters, which are in uninterrupted sequence with preferably high pulse repetition frequency are sent, in addition to the message special Synchronization character for establishing synchronization between the transmission side Pulse code modulation device and the receiver-side evaluation of the pulse code modulation characters are transmitted from the transmitter to the receiver, solved in such a way that one of the message transmission Serving element of a code symbol with a further element of this code symbol is connected in such a way that the further element depends on the former element is brought, and that this combination of two interdependent elements serves as a synchronization indicator and at least one group each, consisting of a number of chronologically successive code characters, number of chronologically successive ones Code character, is assigned.

The connection of the two elements for synchronization takes place expediently so that the further element of the code character in the same or also in the inverse way, like the one connected to it, serving the communication Item is sent.

It is a system that works with pulse amplitude modulation (PAM) became known, in which a measured value is transmitted by a somewhat longer transmission Pulse in a group of pulses, in addition to the transmission of the measured value, a synchronization criterion for the system is transmitted. However, this facility is not comparable with a pulse code modulation system (PCM) according to the invention, in which individual code signals be used in a special way for the synchronization. The extension-one Impulse in PCM would also be considerable both on the transmit side and on the receiver side Difficulties arise because the sampling with PCM is based on a certain pulse duration is cut to size and the pulses are transmitted in uninterrupted sequence. The synchronization system according to the invention has in particular opposite to the above PAM system has the advantage that the synchronization character is not easily can be recognized.

In addition, this type of synchronization for PCM signals is more advantageous Way achieved that a message element of a code character on the receiving side appears twice. This increases the redundancy of the system. The repetition the message element in inverse form is particularly advantageous in many cases regarding the amplifiers in the transmission path.

To increase the redundancy of the system, it is particularly advantageous to to transmit the synchronous elements in each code character and preferably with the to couple the message transmission serving code element that rated the highest will.

Should this synchronization method make efficient use of a Pulse code modulation system can be achieved, so it is advantageous only in each k-th, e.g. B. to insert a synchronous element in every 50th or 100th code character, and although expediently so that, in particular, the lowest code element to be evaluated sent in a fixed relationship to a message element of the same code character will. As a result, the message can be slightly reduced with every kth synchronization character are falsified, since however the element with the lowest value is the synchronous element is used, the resulting error is very small. In contrast is a better one with this method. Utilization of the PCM system achieved since then all positions in the code characters can be occupied by message elements.

On the receiving side is special for the proposed synchronization a device favorable in which a periodic, generated by a pulse generator Key pulse, the pulse repetition time of which differs little from the duration of a code character, in, a closed circuit consisting of the pulse generator, one connected to it Delay line and a decoupling circuit connected to the delay line, is fed in, and that the total runtime within this circle is equal to Duration of a code character is measured that also in one direction the delay line advancing key pulses the advancing in the opposite direction pulse code modulated signal is superimposed and that on the delay line so much Taps guided on the decoupling circuit are attached, such as elements for Identification of the synchronization are provided in a code character, namely at the points on the delay line where synchronization is present the characteristic elements coincide with the tactile pulses.

The decoupling circuit is designed as a logic circuit for this purpose, which emits a pulse at its output if the identification at its inputs serving, fixed pulses of the pulse code modulated signal together with the superimposed key pulse are present.

If two synchronous elements connected to one another are provided for each code character, so two taps must be attached to the delay line, which lead to Lead decoupling. This is the first tap reached by the key pulse via another delay line piece with the same delay time as the one between the two taps lying delay line piece with the decoupling circuit tied together.

Such a receiver-side device is even for very high Pulse repetition frequencies are not expensive and yet reliable.

A synchro-sign is inserted in each code sign, so it is advisable to the pulse generated by the decoupling circuit directly for synchronization of the pulse generator.

For a system in which there is only one synchronous element in every kth code character is inserted, it is expedient to add a further pulse generator in addition to the first pulse generator M1 Provide a pulse generator whose pulse repetition time is equal to the duration of a code character is, and between the two generators a changeover switch, preferably in the form of a Provide monostable multivibrator connected to the decoupling circuit and the second pulse generator after receiving a pulse from the decoupling circuit switches on for approximately the duration of a synchronization period and the first generator turns off.

With this arrangement it is advantageous to use the monostable multivibrator to be replaced by a flip-flop circuit which, after receiving a pulse from the Decoupling circuit turns off the first pulse generator and the second pulse generator turns on.

The flip-flop circuit is expediently connected to the pulse generator connected pulse counting circuit, which is sent to the flip-flop after k-1 periods emits a reset pulse, through which the flip-flop circuit in the original Switching state is shifted.

In advantageous utilization of the delay line, this is at the same time for a serial-parallel converter of the pulse-code-modulated signal, which is usually to be provided used.

The invention is described in greater detail below with the aid of exemplary embodiments explained.

The sending-side insertion of a synchronous element in a code symbol is known per se and therefore does not cause any difficulties. For this reason is shown in Figs. 1, 3 and 4 only the receiving side is shown. The F i g. 2 serves the explanation of FIG. 1. According to the invention, as a synchronization character an element of a code character which serves for the transmission of messages brought with another element of the code character, which is used for synchronization. The connection can be made in such a way that the further element is sent in the same way becomes like the element serving the communication, d. i.e., that of messaging serving code element is present as "1", then the further element is also used as "1" sent, if it is available as "0", the following element is also sent as "0". However, it is particularly advantageous; the second element inversely to the message element to send, d. that is, if the message element is present as "1", the second Element sent as "0" and vice versa. The latter is especially with regard to the Amplifier in the transmission path advantageous.

For the sake of simplicity, it is also expedient to use the synchronizing element to be inserted immediately next to the message element used for coupling. By the double transmission of a message element of the system becomes more advantageous Way, an increase in redundancy is achieved. This is particularly beneficial when the message element used is the element that has the highest significance in the Code characters transmitted.

For such a synchronization method, a circuit is expediently used on the receiving side, which is then shown on the basis of FIGS. 1 in connection with FIG. 2 should be described in more detail. A pulse generator M1 with subsequent pulse shaper F generates a key pulse which is sent to a delay line V. The delay line V has taps 1 to ri, of which the last two a and b are led to a decoupling circuit A. A pulse output of this decoupling circuit leads back to the synchronization input of the pulse generator M1, so that a closed circuit is created. The total transit time within this circle is dimensioned to be equal to one sampling period, ie equal to the duration of a code character of the received pulse-code-modulated signal S. This signal S is fed into the delay line V from the other side. The pulse generator Ml, expediently designed as an astable multivibrator, generates a sampling pulse whose period is initially not equal to the duration of a code symbol, but rather deviates from the duration of a code symbol by the duration of a code element if possible. If, for example, the duration of a code character is 100 nsec and the code character is made up of eight code elements following one another without pauses, then this period should be 112.5 or 87.5 nsec if possible. The key pulse T is applied to the delay line from one side, while the pulse-code-modulated signal is fed into the delay line from the other side. The probe pulse advancing in one direction and the signal advancing in the opposite direction are therefore superimposed on the delay line. The taps attached to the delay line are given by the position of the synchronization characters determined by the transmitter. Are z. B. two adjacent code elements for the synchronization in the manner described are connected to each other, in the example according to FIG. 1, if the n-th is used in conjunction with the (n-1) -th code element, the taps on the delay line must be placed at intervals of half a code element duration. The latter results from the fact that the key pulse and the pulse-code-modulated signal run against one another on the delay line and thus, in relative terms, double the rate of advance is given on the line.

The decoupling circuit consists of a logic circuit combined with a threshold circuit. It emits a pulse at its output when the key pulse appears at its input at the same time as the synchronous elements provided on the transmitter side. For the simultaneous arrival of the pulses at the input of the actual decoupling circuit, an additional short piece of a delay line is connected between the delay line and the input b of the decoupling circuit, the running time of which is as long as the piece of the delay line between the taps n and (n-1). In the numerical example given, the running time of this short piece would be the same ns, i.e. 6.25 nsec.

The coincidence of the key pulse with the synchronous elements at the taps a and b takes place roughly as follows: If a key pulse has arrived at the tap b and also the first synchronous element, both of them are superimposed on the additional delay line on the decoupling circuit. After half a code element duration, the second synchronizing element is advanced to tap a, as is the tactile pulse coming from the other direction. The pulses will appear at the same time at the inputs of the decoupling circuit. Since the pulse code modulated signal is sent with a constant pulse repetition frequency, the synchronous elements of each code character pass taps a and b of the delay line V with the same time interval to the delay line V happen, he is z. B. appear at tap 1 in the first period, tap 2 in the second period, etc., and after some time it will also reach taps a and b. If this is the case, the key pulse and the two synchronizing elements will appear at both inputs of the decoupling circuit at the same time. The decoupling circuit contains a threshold at each of these inputs, which is only exceeded if the key pulse and the corresponding sync pulses are correctly superimposed. If the two synchronous elements are equivalent, an equivalent circuit is required as the logic circuit, ie a pulse appears at the output of the decoupling circuit if both thresholds have been exceeded or neither of the two. If, on the other hand, the synchronous elements in the pulse-code-modulated signal are provided in such a way that the further element of the code symbol is sent in the inverse manner as the message element connected to it, a pulse appears in the synchronized state only at the output of one of the threshold circuits. In this case, the logic circuit must be designed as an exclusive-OR circuit. If a pulse appears at the output of the decoupling circuit, the astable multivibrator M1 is synchronized. This multivibrator M1 immediately emits a pulse. Since the transit time for the scanning circuit is equal to the duration of a code character, this pulse will again encounter the synchronous elements at points n and n-1 of the delay line, and the process is repeated. In this case, synchronization has been achieved.

However, it can also happen that some message element pair temporarily the same combination of values, e.g. B. 1 and 0, like the pair of synchronizing elements Has. Then the synchronization engages in the wrong place, and the key pulse is generated in the wrong phase until another combination appears. From then on, the key pulse shifts again in phase from period to period until the correct position is finally set.

However, since the pulse train time will generally be very short, in the example chosen is the sampling frequency 10 MHz, so can a Message element pair very often the same combination as the synchronous element pair without the synchronization process taking a long time takes. For example, if one assumes 100 [sec. As the maximum permissible time until termination of the synchronization process and the worst case that the phase of the key pulse must go through all n-steps, then it follows that each message element pair may have a maximum of 125 times the same combination in a row as the one used for synchronization certain pairs of elements. From this one can conclude that in most cases the Synchronization process will take place in a much shorter time.

As already mentioned, the sampling period does not necessarily have to differ from the duration of a code symbol by exactly one code element duration. If the key pulse is made relatively long, e.g. B. 10 nsec, while the duration of a code element is 12.5 nsec, so it is not absolutely necessary that the key pulse and the sync pulses exactly at the intended taps, here z. B. meet n and n-1 of the delay line. As the F i g. 2 shows, the probe pulse T or one of the sync pulses Si can deviate from the tap location, which is designated by 0, by the time ± dt. Within this time period ± A t, the threshold indicated by the line Sw is still exceeded and a pulse is emitted. Assuming that the sampling frequency has become a little higher, the meeting point of the two pulses is to the right of tap point 0. The decoupling circuit is therefore excited a little earlier and the sampling pulse is also generated a little earlier. It follows from this that not only may the touch pulse deviate from a predetermined frequency, but also temporarily small fluctuations in the clock frequency generated by the transmitter are permissible.

Should short-term disturbances of the synchronization, e.g. B. by failure of the received signal are bridged, this error can also be switched off. This is possible, for example, by adding an additional, freely oscillating Pulse generator is provided, the frequency of which is based on the transmission-side sampling frequency is matched. A changeover switch must then ensure that after the synchronization process is complete this second pulse generator takes over the function of the first pulse generator. In the event of a brief disturbance in the transmission path, this causes the key pulse still generated in the correct phase for some time. The second pulse generator can also be saved if the first is designed in such a way that it operates on two frequencies can swing. This can be done, for example, that the frequency-determining Elements of this pulse generator are switched.

The applicability of the circuit arrangement according to the invention is not limited to the type of synchronization according to the invention by repeating one of the message elements. Rather, it is also suitable for synchronization with any modulated synchronous pulse. A selection for these cases is given in the table below. This results in; that only the taps on the delay line and the design of the decoupling circuit, in particular the logic circuit, have to be adapted to the present synchronization system. Repetition of a two taps code element with equivalent circuit of the same value Repetition of a two tapping point code element with exclusive-or-inverse value circuit Synchronous element decoupling circuit Always "1" a tap, amplifier (1 ->1; 0-3 0) Always "0" a tap, inverter (0 -. 1; 1-> 0) Alternating »10« a tap point, screen tray or »01«, which is half the amount sampling frequency one pulse each pulse. Chain code a tap point, on chain code selective circuit that each emits a pulse. As already explained, the synchronization locks into place very quickly, especially in systems with a high pulse repetition frequency. This is not necessary in every case, but much longer periods of time are often permissible for synchronization. For this reason, it is sufficient in many applications to only add a synchronous element to every k-th code character, e.g. B. every 50th or 100th

In this case, in an expedient development of the invention, FIG every k-th code character the message element with the least message content replaced by a synchronous element so that it can be used as a direct or inverse repetition a message element from the same code character is sent.

With this type of synchronization you have to ensure full occupancy of all places in the code symbol due to message elements an additional quantization noise accept due to a slight falsification of the message.

This variant of the synchronization can be carried out with a receiver-side circuit as shown in FIG. 3 is outlined. This circuit is basically just an extension of the circuit after the F i g. 1 and the additional elements are: a changeover switch M2, which is used as a monostable Multivibrator can be run, and another pulse generator M3, which as astable multivibrator can be formed. The originally intended pulse generator, which oscillates at a frequency deviating from the sampling period is shown in FIG labeled M1. All other elements are compared to FIG. 1 unchanged stayed and named the same.

The mode of operation of this circuit is as follows: The pulse generator M1 generates probe pulses with a subsequent period that differs from the duration of a code character. The running time in the closed circuit, consisting of the delay line V, the decoupling circuit A, the pulse generators Ml and M2 and the pulse shaper F, is in turn chosen to be equal to the duration of a code character to. In the same numerical example, the oscillation frequency fl of the generator M1 would be fi = n + -1-.fT 8 f1 = 8 + - # 10 MHz = 8.9 MHz. Here, n is the number of message elements in a code symbol and fT is the sampling frequency on the transmission side. The changeover switch M2 has switched on the multivibrator M 1 in the rest position. If the key pulse is present at the inputs of the decoupling stages a and b together with the provided synchronous elements, the decoupling circuit in turn emits a pulse which is sent to the monostable multivibrator M2. This pulse switches M2 to the astable multivibrator M3, which, as long as pulses appear from the decoupling stage, is synchronized by it and thus continues to oscillate at the sampling frequency fT, in the selected numerical example 10 MHz. The unstable position of the multivibrator M 2 remains somewhat shorter than the duration of a synchronization period kx to is. If the pair of elements triggering the monostable multivibrator M2 was not the one intended for synchronization, then after k periods no pulse appears from the decoupling circuit, and M2 switches the multivibrator M1 on again; the search process for the synchronous elements begins again. M 1 is active again and delivers the next sampling pulse one sampling period and one element duration later. As with the FIG. 1, all pairs of elements are checked one after the other until the correct pair of elements intended for synchronization appears on the decoupling circuit. If this is the case, the multivibrator M2 is switched to the astable position so that the pulse generator M3 is switched on. For the next k-1 periods in which no synchronous element was inserted on the transmit side, it supplies in-phase scanning pulses.

Another advantageous implementation of the synchronization process can be with the in F i g. 4 to achieve the circuit shown. This circuit arrangement works even more precisely. In order to achieve a precise tilting back of the switch M2, if this is designed as a flip-flop circuit, it is reset to the initial position (M 1 switched on) is effected by a pulse counting circuit Z. She still worried k-1 periods of the multivibrator M3 the resetting of the switch M2. Then gives in the k-th period the decoupling circuit releases a pulse, M2 switches immediately back to M3 and counting begins again; otherwise M 1 takes over the further search process.

The in the F i g. 1, 3 and 4 shown delay line V can in an extremely advantageous manner to a part at the same time for the series parallel implementation of the pulse code modulated signal can be used. You will do this with the necessary Provide taps. Once synchronization has taken place, the taps 1 to h correctly timed according to code elements, the pulse-code-modulated message be removed. For this purpose, there are threshold circuits behind the taps to switch on, which at the same time when a key pulse and a code pulse appear Time to give an impulse. By combining the synchronizing and receiving side Series-parallel converter circuit can achieve a more rational utilization of the system will.

Claims (7)

Claims: 1. System for the transmission of signals in the form of Pulse code modulation characters, which are in uninterrupted sequence with preferably high Pulse frequency are sent, with which, in addition to the message, special synchronization characters for establishing synchronization between the pulse code modulation device on the transmitter side and the receiver-side evaluation of the pulse code modulation characters from the transmitter to the Recipients are transmitted, d a d u r c h e -k e n n n z e i c h n e t that a the message transmission element of a code character with another Element of this code character is connected in such a way that the further element is dependent is brought from the first element, and that this combination of two interdependent Elements serving as synchronization indicators and each consisting of at least one group from a number of chronologically consecutive code characters, but preferably is assigned to each individual code character. 2. System according to claim 1, characterized in that that the further element of the code character is in the same way as the one connected to it, message serving element is sent. 3. System according to claim 1, characterized in that the further element in the inverse manner as that with connected to the message transmission element is sent. 4. System according to claim 2 or 3, characterized in that the further code element directly is adjacent to the message transmission serving code element, preferably this immediately follows. 5. System according to one of claims 1 to 4, characterized in that that the synchronous elements are transmitted in each code character. 6. System according to Claim 5, characterized in that the synchronizing element with that of the message transmission serving code element is coupled, which is rated the highest. 7. System according to one of claims 1 to 4, characterized in that the synchronizing elements only in every kth, e.g. B. are inserted in every 50th or 100th code character, namely so that the synchronous element is the lowest message element to be rated each code character is replaced and in a fixed relationship to another message element of the same code character is sent. B. System according to one of the preceding Claims, characterized in that on the receiving side a periodic of a pulse generator generated tactile pulse, its pulse repetition time themselves preferably differs by the duration of a code element from the duration of a code character, in a closed circuit, consisting of the pulse generator with one attached to it connected delay line and one connected to the delay line Decoupling circuit is fed, and that the total running time within this Circle is measured equal to the duration of a code character that also in the a direction on the delay line advancing key pulses that in Opposite direction advancing pulse code modulated signal is superimposed and that on the delay line so much taps led to the decoupling circuit are attached, such as elements for identifying the synchronization in a code symbol are provided, namely at the points of the delay line where when present the synchronization, the characteristic elements meet with the tactile pulses. 9. System according to claim 8, characterized in that the decoupling circuit as logic circuit is formed which emits a pulse at its output when at their inputs the fixed impulses of the pulse-code-modulated signal used for identification are present together with the superimposed key pulse. 10. System according to claim 9, characterized in that with two on the decoupling circuit guided taps the first tap reached by the key pulse via another Delay line piece with the same running time as the one between the two taps lying delay line piece is connected to the decoupling circuit. 11. System according to one of Claims 3 and 4 and one of Claims 8 to 10, characterized characterized in that the pulse generated by the decoupling circuit for synchronization of the pulse generator, preferably a multivibrator, is provided. 12. System according to claim 11, characterized in that a further pulse generator is provided is whose pulse repetition time is equal to the duration of a code character, and that this Pulse generator after synchronization the function of the first pulse generator takes over. 13. System according to claim 12, characterized in that the first pulse generator can be switched to both pulse repetition frequencies. 14. System according to one of the claims 7 to 9, characterized in that in addition to the first pulse generator (M1) another Pulse generator (M3) is provided, the pulse repetition time of which is equal to the duration (to) of a code character, and that a changeover switch, preferably between the two generators is provided in the form of a monostable multivibrator (M2), which is connected to the decoupling circuit is connected and approximately after receiving a pulse from the decoupling circuit the second pulse generator (M3) for the duration of a synchronization period (kxto) switches on and switches off the generator (M1). 15. System according to claim 14, characterized characterized in that the monostable multivibrator (M2) by a flip-flop circuit is replaced, the first after receiving a pulse from the decoupling circuit Switches off the pulse generator (M1) and switches on the second pulse generator (M3). 16. System according to claim 15, characterized in that the flip-flop circuit after k-1 periods of the second pulse generator (M3) by a pulse counting circuit (Z), which is fed by the second pulse generator (M3), a reset pulse which puts it in the original switching state (M1 switched on) will. 17. System according to one of the preceding claims, characterized in that that part of the delay line contained in the synchronization circuit at the same time is used for serial parallel conversion of the pulse code modulated signal. Into consideration Drawn pamphlets: Austrian patent specification number 175 933.