Electric signal synchronising apparatus

Holder: Idem (71)

Agent: Armengaud Aîné, 21, boulevard Poissonnière, Paris (2).

Synchronization device for radio signal receivers.

72) Invention of:

33) (32) (31

Conventional priority: Patent application filed in Japan on May 27, 1971,

not. 36.836 / 1971 in the name of Kiyotaka Furuno.

Sale of booklets at ['IMPRIMERIE NATIONALE, 27, rue de la Convention - PARIS (15^e)

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The present invention relates to a new and improved synchronization dev ice which is particularly useful in a device intended to measure a time difference or a phase difference between two incident signals.

Devices such as the Loran and Omega '' receivers, which are intended to measure a time or phase difference between two incident signals in order to find the position of a navigating body, are designed to generate two waves in the device which are respectively synchronous with respect to the incident signals and then to measure the time or phase difference between these two synchronous waves generated. When the incident signals are received by a navigating body, such as an airplane, moving at high speed, the incident signals are subjected to the Doppler effect and the period of the synchronous waves generated must therefore be corrected or compensated for by amount corresponding to the Doppler effect.

In the omega navigation system, for example, a series of transmitting stations transmit their signals on the same frequency in a shared manner over time. Therefore, in order to compare two signals from two transmitting stations and to measure the phase difference between them, it is necessary to store or keep one signal until the other is received. As each station emits its signal in the form of a train of segments appearing at a predetermined time, the Doppler effect measured on a segment must be stored in a certain form until the next segment is received.

A first way of performing the above operation is to compare a signal of the segment in phase with a synchronous wave which is produced by frequency division of a reference signal which is a higher harmonic thereof, and to store the phase difference as an electrical charge in a capacitor. The capacitor charge is then converted into a capacitor using a variable capacitance diode or the like and the frequency of the reference frequency generator is thus controlled, so that the synchronous wave takes the same phase as the signal. incident. In the case of an omega receiver, however, it provides for a certain number of reference frequency generators since a certain number of synchronous waves corresponding to the signals of the various stations must be processed individually. As the reference frequency generators must

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-22139118 have very high precision, the resulting device is very expensive. In addition, when the reference frequency is changed, it cannot be used as a time reference to measure a time or phase difference of the incident signals. Finally, by controlling the frequency of the reference generator based on the amount of Doppler effect detected, it can be difficult to obtain that the period of the synchronous wave largely follows the speed of the navigating body.

The invention therefore aims to provide an improved synchronization device based on a new principle, in which a certain number of synchronous waves are recorded from a single common reference frequency generator and in which is followed by these waves synchronize the respective signals emitted by a certain number of transmitting stations.

According to the invention, the synchronization device comprises a receiver intended to receive the incident signals, a frequency generator ^ / àesTine³^. generating a reference signal having a constant frequency, a frequency divider for dividing the frequency of the reference signal to produce a synchronous wave having the same frequency as the incident signal, a comparator for comparing the synchronous wave to the incident signal in order to detecting a phase difference, a device for storing the phase difference detected during the period between one signal segment and the next, a device for producing a train of control pulses which also divides the period of the segments into n parts, n being proportional to the detected phase difference, and a device for shifting the phase of the synchronous wave by l / n of the phase difference detected at each instant of application of the command pulse train, so that the phase difference is canceled before the next segment is received.

Other characteristics and advantages of the invention will appear during the following description, given solely by way of example and made with reference to the appended drawings, in which:

- Figure 1 is a block diagram of an embodiment of the device of the invention;

- Figure 2 is a diagram showing several waveforms produced in the device of Figure 1, to facilitate the description of the operation of the device;

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FIG. 3 is a block diagram of an embodiment of the trigger signal generator of the device in FIG. 1; and

- Figure 4 is a block diagram of another embodiment 5 of the device of the invention.

Referring now to Figure 1, the omega '' receiver assembly includes an omega 2 receiver with an antenna 1, a comparator 3, a frequency divider and phase shifter 4 and a reference frequency generator 5. L 'set includes' 10 further a memory 6, a trigger signal generator 7, a frequency divider 8, a door 9 and a pulse counter 10, which form the synchronization device according to the invention.

We will now describe the operation of the re15 device presented in Figure 1, using various waveforms.

As is well known in this field, the omega 2 receiver receives from the antenna 1 a signal a. which contains a series of waves A, B, C, D, E, P, G, and H for example, emitted respectively by eight transmitting stations in a manner divided in time and at the same frequency. As each transmitting station is designed so as to transmit the corresponding wave for a short duration Τθ, from 0.9 to 1.2 seconds for example, at each period T of 10 seconds for example, the wave coming from the same station appears at each instant T. Consequently, the wave emitted by any desired station can be picked up in the receiver 2 by a switching wave b having a period T and a duration Τθ. As an example, the drawing shows that the B wave is picked up. The received wave B is then amplified and shaped in the receiver 2 and has a rectangular shape £.

On the other hand, the generator 5 generates a train of reference clock pulses REP which is divided in frequency by the frequency divider 4 to form a synchronous wave having the same frequency as the incident wave B. This synchronous wave is then shaped and becomes a rectangular wave d having the same shape as the wave £. The waves e and d are applied to the comparator 3 and compared in phase and a detected phase difference / is temporarily stored in the memory 6. The Phase difference information Æ0 is then applied to the trigger signal generator 7.

The REF reference frequency pulse train is

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-42139118 then applied to the frequency divider 8 to form a train of clock pulses e having a constant period t. The period _t of the pulse train £ can be arbitrary but it is preferably chosen to be one hundredth of the period T of the signal of mutation b. For example, it can be 0.1 seconds when T is 10 seconds.

The trigger pulse generator 7 receives the clock pulse e from the frequency divider 8 and the phase difference signal 00 from the memory 6 and produces a trigger signal f which has a period t equal to that of l clock pulse £ and a duration w proportional to the phase difference

Δ0. This trigger signal is applied as a control signal to the door circuit 9 to open it during each period corresponding to the duration w, so that the train REP is transmitted!

intermittently through gate 9 to form an output waveform shown in g in Figure 2.

The g wave is applied to the pulse counter 10. This is intended to produce a pulse each time it receives a predetermined number N of pulses. Consequently, if a number m of pulses of reference frequency is contained in the duration w of the waveform f, the period of the train of pulses h produced by the counter 10 is t (N / m), and a number n of Zaç pEKdtaikaa pulses is produced by the counter 10 during the period T of the switching signal b when n = T / T · ^ = Tm / tN. As T, _t and N are chosen beforehand and fixed, n is proportional to m which is also proportional to the duration w which is itself proportional to the phase difference Δ0, so that n is perfectly proportional to Δ0.

Consequently, if the phase shifter 4 is designed beforehand d so as to shift the input wave phase by 0 / n each time the pulse h is received, the phase difference is fully compensated during the period T, c ' that is to say before the next incident signal B is received by the receiver 2. When the phase difference is K Δ0, arbit is an arbitrary constant, the phase shift

Δ0 / η is executed Kn times during period T to compensate for the phase difference ΚΔ0. Although the phase shift operation can be carried out in the phase shifter 4 using any of the known techniques, it is conveniently carried out by sampling or adding a particular number of pulses in or to the clock pulses produced by the divider frequency

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-52139118 for each incident pulse h for example.

Assuming that T = 10 s, t = 0.1 s, N = 100, m = 5 and that the synchronous wave d gains 40 * in phase with respect to the incident wave £ as an example, the pulse h is produced every twenty pulses of g, that is to say every two seconds and consequently there are produced five pulses h by the pulse counter 10. Consequently, the phase of the synchronous wave d is delayed five times by 40/5 each time.

If the phase difference detected is 2 40, the phase shift is carried out ten times by the same amount 40/5 each time.

Thus, if the degree of phase shift to be performed each time in the phase shifter 4 is calibrated once for a certain phase difference, any phase difference detected by the comparator 5 can be corrected completely before the next desired signal enters the receiver 2 and any Doppler effect can be canceled automatically.

As is clear from the above, the reference frequency generator 5 is entirely independent of the phase shifting operation of the device. As a result, it can also be noted that the single reference frequency generator is sufficient to detect the phase of any pair of incident signals since it can be used in common for a series of analog synchronization devices which process different synchronous waves.

A description will now be given of the operation for producing trigger signals carried out in the generator 7 with reference to the assembly of FIG. 5 by way of example.

In FIG. 5 * 1® generator 7 of trigger signals comprises a coincidence door 11, a counting circuit 12 and a rocker 15. In this case, the comparator 5 comprises a counter circuit constituted by rockers arranged in a series stages to digitally count the phase difference 40. The memory circuit 6 also includes the same number of rocker stages as the counting circuit of the comparator 5 and the memory operation is carried out by making the state of each rocker of the memory circuit coincide with that of each corresponding rocker of the comparator.

On the other hand, the clock pulse e produced by the frequency divider 8 is applied to the trigger terminal T of the rocker 15 to cause the terminal Q to go from the low level to the level

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-62 139 119 high. Since the Q and K terminals are connected to each other, the Q terminal is never brought back to the low level unless the rocker is reset. At the high level of terminal Q, the gate circuit 9 is made conductive in order to allow the reference clock pulses REP coming from the generator 5 to pass.

The output pulses g of the gate circuit 9 are applied to the pulse counter 10, and, simultaneously, are counted by the pulse counter 12 of the generator 7. The counter 12 is made up of cascaded rockers of the same stages as the memory circuit 5 and the output of each rocker is compared in the door circuit to coincide with the content of each corresponding rocker of memory 5.

The coincidence door 11 is intended to produce an output when the two corresponding rockers of the memory circuit 6 and of the counter circuit 12 are in the same state, respectively and at the same instant, that is to say when the numerical value ( phase difference) stored in memory 6 coincides with the digital value (count) of counting circuit 12.

The output of the coincidence door 11 is applied to the counter circuit 12 to reset it and, simultaneously, to the reset terminal R of the rocker 15 to also reset it. When the rocker 15 is reset to zero, the terminal Q is switched to the low state and the gate circuit 9 becomes non-conductive to block the reference clock pulses REP. As is clear from the above, the rocker 13 produces a pulse which appears on each application of the clock pulse e_ coming from the frequency divider 8 and which continues for a duration w corresponding to the phase difference Δ0 stored in memory 6, as shown in f in FIG. 2.

In the above operation, the phase difference is indicated by the number of clock pulses and this number is accumulated. The same operation can be carried out by indicating the phase difference in the form of a binary code and by adding a binary code to each appearance of the clock pulse £ coming from the frequency divider 8. This device will be described in relation with figure 4.

In the device of FIG. 4, the rectangles 7 »9 and 10 of FIG. 1 are replaced by a single arithmetic unit 20 comprising an adder 21 and an accumulator 22. In this case, the phase difference Δ0 is stored in the memory 6 in the form of a binary code, for example 0011 when Δ0 = 3 ·

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The binary code is applied from memory 6 to an input of adder 21. The other input of adder 21 is applied with the output of accumulator 22 whose input is connected to the output of l adder 21. The third input of adder 21 is the clock pulse £ applied from the frequency divider 8. The adder 21 successively adds the output of memory 6 to the output of accumulator 22 each time that the clock pulse e is applied, as indicated in Table 1 in which the phase difference Δ0 is represented by 3, ie 0011. When the most significant digit goes from l to 0, a carry-over pulse ”is produced by the adder 21 and is applied to the phase shifter 4 in the form of the control pulse h. As will be easily understood, the duration of this transfer pulse is inversely proportional to the value of Δ0 and, consequently, the number which corresponds to it and belonging to the switching signal period b is proportional to the phase difference. Consequently, the transfer pulse train is equivalent to the pulse train h of the device of FIGS. 1 and

Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. The assemblies indicated in the respective rectangles of the drawings are familiar to specialists. In addition, although the description has focused on the omega reception device, it will be noted that the invention also applies to Loran devices and the like.

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