Abstract:
The invention relates to a digital signal transfer method and apparatus in which signals are transferred between first and second electrically isolated circuits. An announcement signal is transferred from the first circuit to the second circuit and a data signal is transferred from the first circuit to the second circuit within a data signal time window associated with the announcement signal.

Description:
RELATED U.S. APPLICATION DATA 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/570,082 filed on Sep. 30, 2009, which in turn is a divisional application of U.S. application Ser. No. 11/776,390 filed Jul. 11, 2007, which in turn is a continuation of U.S. application Ser. No. 10/666,221, filed Sep. 18, 2003, now abandoned. Each of the prior filed applications is hereby fully incorporated herein by reference. 
     
    
     FOREIGN APPLICATION PRIORITY DATA 
       [0002]    The present application claims priority to German patent application no. DE10243197.3, filed Sep. 18, 2002, the disclosure of which is hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates to a digital signal transfer method, particularly for transferring a digital signal via a potential barrier. 
       BACKGROUND 
       [0004]    The transfer of digital control signals and data signals via a potential barrier is frequently necessary in electrical installations in order to electrically isolate different circuits, for example, a circuit which produces a control signal and a circuit which processes the control signal, from one another. To reduce the number of coupling points between such circuits, which are to be electrically isolated, and data lines, serial transfer methods are frequently used. Thus, by way of example, microcontrollers (IC) use interfaces of the RS-485 type or use SPI (Serial Parallel Interface) interfaces to communicate with circuit components that are to be actuated. In this context, it is desirable to transfer data at a high transfer rate and to isolate potentials between the microcontroller and the circuits that are to be actuated. In addition, the transfer method needs to be highly immune to interference. 
         [0005]    For data transfer with electrical isolation between a transmitter circuit and a receiver circuit, it is known practice to use transformers, particularly planar transformers integrated on an IC, as described in Published German Patent Application 101 00 282 A1, for example, as data couplers. To transfer signals using such transformers, it is necessary to convert the signals into pulse trains that are suitable for transfer, and it is known practice, for example, to produce cyclic pulse trains from a binary control signal and to transfer them, as described in U.S. Pat. Nos. 4,027,152, 4,748,419, 5,952,849 and 6,262,600, for example. 
         [0006]    Planar transformers integrated in an integrated circuit, which are also called coreless transformers, are capable of transferring data at a speed of up to 1 Gbaud, where not just the high data transfer speed, but also the low power consumption with good immunity to interference make such transformers attractive as coupling modules in data transfer links. 
       SUMMARY 
       [0007]    It is accordingly an object of the invention to provide a digital signal transfer method that overcomes the above-mentioned disadvantages of the prior art methods of this general type. In particular, it is an object of the invention to provide a fast and secure data transfer method, particularly a transfer method that is suitable for data transfer using integrated transformers as coupling modules. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention, an embodiment of the inventive digital signal transfer method in which a first and a second transfer channel are provided. The first transfer channel is used as an “announcement channel” for data transfer and the second transfer channel is used as an actual data channel. To transfer a data signal, an announcement signal including at least one pulse is first transferred via the first transfer channel. The data signal is subsequently transferred via the second transfer channel within a data signal time window lasting for a prescribed period after the announcement signal. 
         [0009]    The inventive method involves the announcement signal and the data signal being transferred at different times via separate transfer channels, which ensures a very high level of immunity to interference. The likelihood of an interference signal which appears on the data channel being incorrectly identified as a useful signal is low in the case of the inventive method, because the receiver accepts only such signals that are received within the data signal time window after the announcement signal. 
         [0010]    Preferably, the transfer channels each include a magnetic coupling element, particularly a transformer integrated in an integrated circuit. The use of two transfer channels, with announcement signals being transferred on the first transfer channel and the data signal being transferred on the second transfer channel, at different times from one another, also reduces immunity to interference, when transformers are used as coupling elements, because electromagnetic interference appears in the two transformers in common mode, i.e., the interference brings about signals which occur simultaneously and whose signal profiles are the same. Such interference signals are easy to detect in a receiver circuit and are correspondingly easy to isolate from the useful signal. 
         [0011]    Preferably, the data signal time window within which data signals are transferred starts after a period which is greater than zero after the announcement signal. By way of example, the announcement signal includes just a single pulse, and the data signal time window does not start until after the end of this announcement pulse. 
         [0012]    In one embodiment of the invention, a further transfer channel is provided which is used to transfer control information. Such control information includes a parity check signal or a transfer check signal, for example. Preferably, the data signal is transferred within the respective data signal time window in coded form in order to increase redundancy and hence to increase immunity to interference further, and any coding methods which increase redundancy can be used for this. In the simplest case, a data pulse or a data pulse train is repeated within the data signal time window, that is to say is transferred a plurality of times at successive times. 
         [0013]    The inventive method is also suitable for transferring a binary signal that has a first or a second signal level. Such signal profiles, in which a signal assumes a first signal level or a second signal level over a comparatively long period, which is much longer than the data signal time window, are typical of control signals, for example turn-on and turn-off signals for loads, which need to be transferred in electrical installations with isolation of potentials. In one embodiment of the inventive method for transferring such control signals, provision is made for announcement pulses to be transferred at regular intervals of time and for respective pulse trains that represent the first or the second signal level to be transferred during the data signal time windows which follow the announcement signals. In the simplest case, a pulse is transferred during the data signal time window when the control signal assumes a first signal level, and no pulse is transferred when the control signal assumes a second signal level. The transfer, repeated at cyclic intervals of time, of pulse trains which represent the signal level of the control signal helps to increase immunity to interference during the transfer of such control signals, since even if interference arises during a data signal time window and makes data transfer impossible, the data signal is transferred during one of the subsequent data signal time windows, after the interference has declined. 
         [0014]    With the foregoing and other objects in view there is also provided, in accordance with the invention, a digital signal transfer method that includes providing a transfer channel. An announcement signal including at least one pulse is transmitted via the transfer channel. A data signal is also transmitted via the transfer channel within a data signal time window lasting for a prescribed period after the announcement signal. 
         [0015]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0016]    Although the invention is illustrated and described herein as embodied in a digital signal transfer method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0017]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a block diagram of a data transfer link having two transfer channels that each include a coupling element for isolating potentials in a transmitter circuit and a receiver circuit. 
           [0019]      FIG. 2  is a diagram showing exemplary signal profiles of signals on the first and second transfer channels. 
           [0020]      FIG. 3A  is a diagram showing exemplary signal profiles of signals, on the first and second transfer channels and also time profiles for selected internal signals in a transmitter circuit and a receiver circuit, which occur in one embodiment of a transfer method. 
           [0021]      FIG. 3B  is a diagram showing exemplary signal profiles of signals, on the first and second transfer channels and also on a third channel that is used as control information channel, which occur in a modification of the method. 
           [0022]      FIG. 4  is a diagram showing selected signal profiles for a method for transferring a binary control signal with regular announcement pulses. 
           [0023]      FIG. 5  is a diagram showing selected signal profiles for a method for transferring a binary control signal with event-controlled announcement pulses. 
           [0024]      FIG. 6  is a block diagram of a data transfer link having a single transfer channel that includes a coupling element for isolating potentials in a transmitter circuit and a receiver circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Unless otherwise indicated, the same reference symbols denote the same circuit components and signals having the same meaning in the figures. 
         [0026]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is schematically shown a data transfer link with a transmitter circuit  10 , to which an input signal Sin is supplied, and a receiver circuit  20  which provides an output signal Sout which is dependent on the input signal Sin. The data transfer link also includes a first transfer channel with a coupling element TR 1  and a second transfer channel with a second coupling element TR 2 . The coupling elements TR 1 , TR 2  preferably each include an integrated transformer for isolating the potentials of the transmitter circuit  10  and the receiver circuit  20 . 
         [0027]    In the case of the transfer link shown, the first transfer channel is used as an announcement channel to transfer an announcement signal S 1  when data transfer needs to take place. The second transfer channel is used as the actual data channel to transfer the actual data signal containing the useful information to the receiver. Both the announcement signal S 1  and the data signal S 2  are individual pulses or pulse trains that are generated by the transmitter circuit  10 . The length of the individual pulses is matched to the transfer properties of the coupling elements TR 1 , TR 2  in order for these pulses to be transferred optimally on interference-free channels. As is sufficiently well known, each of the transformers TR 1 , TR 2  includes a primary coil which is excited by the signal S 1  or S 2  generated by the transmitter circuit  10 . The magnetic coupling of the primary coil and the secondary coil mean that the transmitter-end pulse trains result in corresponding receiver-end pulse trains that are detected by the receiver circuit  20 . 
         [0028]      FIG. 2  fundamentally shows the signal profiles for the announcement signal S 1  and the data signal S 2  in the inventive method. The method provides for the first transfer channel, which serves as the announcement channel, to be used to transfer an announcement signal S 1 . The method also includes transferring a pulse or a pulse train for the data signal within a respective time window lasting for a prescribed period after a pulse or a pulse train for the announcement signal. In the example shown in  FIG. 1 , the announcement signal transferred via the announcement channel is a respective individual announcement pulse. A period td after the start of the announcement pulse is followed by the start of a time window, lasting for a period tf, within which the data signal is transferred. The data signal includes just one data pulse per time window in the example shown in  FIG. 2 . The period td after which the data signal time window starts is longer in this case than the pulse length of the announcement pulse, which means that the time window does not start until after the end of the announcement pulse, as a result of which the announcement pulses and the data pulses following the announcement pulses within the time windows are transferred at different times from one another, resulting in immunity to interference when using the method. 
         [0029]    The data pulse train transferred during the data signal time window can contain the information that is to be transferred in virtually any manner. Thus, by way of example, just one pulse can be transferred during a data signal time window such that the information which is to be transferred is held in the period, for example, by which this pulse is additionally shifted with respect to the start of the data signal time window. In addition, a plurality of, for example n, pulses representing that single bits of a data word of a length of n bits to be transferred, can be transferred during a data signal time window. 
         [0030]    The transmitter and the receiver are synchronized in the inventive method by virtue of the shape of the announcement signal generated by the transmitter, the period for which the data signal time window lasts, and also because the interval of time between the announcement signal and the data signal time window is known at the receiver. Whenever an announcement signal is received, this results in the receiver taking the known information about the period for which the data signal time window lasts and the latter&#39;s distance from the announcement signal as a basis for producing a time window within which pulses which are received on the data channel at the receiver are accepted as a data signal. 
         [0031]    If the transmitter circuit  10  contains a coder which codes the signal transferred within the data signal time windows, the receiver circuit contains a corresponding decoder which provides the output signal Sout from the signals received via the data channel within the data signal time windows. 
         [0032]      FIGS. 3A and 3B  illustrate an exemplary embodiment of the inventive method, in which announcement pulses in the announcement signal S 1  are generated cyclically in time with a clock signal Ts having a clock period tc. In time with this clock signal, an input signal Sin is also available which is shown by way of example as a binary signal whose level can change in time with the clock signal Ts. Such signals appear at the outputs of shift registers, for example. The information about the current level of the input signal Sin is transferred in data signal time windows of length tf. The start of these data signal time windows respectively come a period td after the start of an announcement pulse. The signal level of the input signal Sin is converted into the pulses transferred during the data signal time window by virtue of transferring two pulses at successive times in the data signal time window for a first level, for example, an upper level, of the input signal Sin, while no pulses are generated and transferred during the time window for a second level, for example, a lower level, of the input signal Sin. The transfer of two successive pulses serves for redundancy and hence to increase the immunity to interference. 
         [0033]    The receiver circuit  20  contains a shift register. The content of this shift register is shown in  FIG. 3A . This shift register has a logic one written to it whenever two pulses are detected during the data signal time window. In the case of the fourth data signal time window shown in  FIGS. 3A and 3B , there is a transfer error, because only one pulse is being transferred instead of two pulses. This one pulse is not sufficient for a logic one to be written to the shift register. If no pulses are transferred during a data signal time window after an announcement pulse, a logic zero is written to the shift register. 
         [0034]    In the method shown in  FIG. 3A , provision is also made for a parity signal announcement pulse to be transferred via the announcement channel and for the associated parity signal to be transferred via the data channel within a data signal time window lasting for the period tf. This method involves the stipulation that every nth pulse of the announcement signal  51  is an announcement pulse for a parity signal or that a parity signal is transferred during every nth data signal time window. For the data transfer of 8-bit data words, every ninth announcement pulse is an announcement pulse for a parity signal. 
         [0035]    In the case of the method shown in  FIG. 3A , the receiver  20  generates an internal transfer signal after a period is after the parity signal announcement pulse. The internal transfer signal governs the reading of the shift register described above for the purpose of generating the output signal Sout, provided that the parity check performed on the basis of the parity signal delivers a correct result. 
         [0036]      FIG. 3B  shows a modification of the method shown in  FIG. 3A  in which a third transfer channel is provided, which is shown in dashes in  FIG. 1  and which likewise has a coupling element, preferably a magnetic coupling element, used to transfer a parity signal announcement pulse whenever the transfer of a data word has ended. Additionally, a parity signal is transferred via the data channel during a data signal time window lasting for the period tf after this parity signal announcement pulse. The provision of a separate channel for the parity signal announcement pulse reduces the systems susceptibility to interference and also makes the system more flexible for transferring data words of different length. Hence, a parity check is not performed until a parity signal announcement pulse is received on the further channel. 
         [0037]    The method shown in  FIG. 3B  also has provision for the further channel to be used to transfer a stop pulse which governs the generation of the internal transfer signal, which in turn governs the reading of the shift register to which the data from the data channel have previously been written. To increase immunity to interference, a pulse is transferred on the announcement channel, preferably simultaneously with the stop pulse. An internal transfer signal for reading the shift register and for outputting the output signal Sout is produced at the output of the receiver  20  only when the receiver receives the stop pulse and the pulse on the announcement channel. 
         [0038]      FIG. 4  illustrates an exemplary embodiment of a method for transferring the information contained in a control signal Sin. The control signal Sin is a binary signal which assumes an upper or a lower level. The respective level is present for a period which is normally much longer than the period for which a data signal time window lasts. For transferring such a signal, provision is made for the announcement channel to be used to transfer announcement pulses at regular intervals of time and to transfer at least one pulse containing information about the current signal level of the control signal Sin within data signal time windows, lasting for the period tf, the start of which respectively comes a period td after the start of an announcement pulse. In the exemplary embodiment shown in  FIG. 4 , a pulse is transferred within the time window tf when the input signal Sin assumes an upper signal level, and no pulse is transferred within the data signal time window when the input signal Sin assumes a lower signal level. 
         [0039]    The inventive method thus involves transferring pulses that indicate the current level of the input signal Sin at regular intervals of time. The result of this is a high level of immunity to interference, since even if interference arises during one or more data signal time windows, a correct pulse is transferred sooner or later. 
         [0040]    In the signal profile shown in  FIG. 4 , the input signal Sin changes from a lower level to an upper level at a time t 1 . The information about this level change is transferred with a time delay after a period tdp in the method. This period tdp results from the interval of time td between the announcement pulse and the data signal time window and from the interval of time between the level change in the input signal Sin and the announcement pulse. Accordingly, a delay tdn is produced when the signal level changes from an upper level to a lower level of the input signal Sin, which accordingly results from a delay time between the time t 2  at which the level change takes place and the time of the next announcement pulse and from the interval of time td between the announcement pulse and the data signal time window to which the information about the level change which has taken place is transferred. 
         [0041]      FIG. 5  illustrates a modification to the method for transferring a binary signal Sin which is explained with reference to  FIG. 4 . This method involves first generating the announcement pulses cyclically, as can be seen, in particular, from the first time period, during which the signal assumes a high level. In addition, the announcement pulses are generated on an event-controlled basis when there is a level change in the input signal Sin, in order to reduce the delay time between the level change and the data signal&#39;s pulse which represents this level change as compared with the method in  FIG. 4 . From the time profile for the announcement signal S 1  in  FIG. 5 , it becomes clear that, besides the cyclically recurring announcement pulses, further announcement pulses are present whose appearance is dependent on a level change in the input signal Sin. The delay time which elapses during this method in line with  FIG. 5  between a rising edge of the input signal Sin and the transmission of a useful pulse which represents this edge corresponds essentially to the period td, provided that the useful pulse is transferred immediately at the start of the data signal time window. The maximum time delay between a level change in the input signal Sin and the output signal Sout is tdn=tp+tf, where tp is again the period between the start of an announcement pulse and a data signal time window, and tf is the length of the data signal time window. This delay time arises when the signal level of the input signal changes from an upper signal level to a lower signal level. This information is transferred by not transferring a pulse during the data signal time window, which means that it is necessary to wait the length of this time window until the output signal Sout changes its level. 
         [0042]    In the method explained up to now, announcement pulses S 1  announcing a data transfer and data pulses S 2  are transferred via physically separate channels TR 1 , TR 2  in order to increase immunity to interference. If a reduction in the immunity to interference is acceptable, then one modification to the method explained up to now has provision for the announcement pulses S 1  and the data pulses S 2  to be transferred via just one common channel  30  as depicted in  FIG. 6  instead of via separate channels. In this case, the data pulses S 2  are each transferred within a data signal time window of prescribed length which comes after an announcement pulse S 1  in time, with, as in the case of the method explained previously, the receiver “accepting” only such data pulses that are transferred within the data signal time window after an announcement signal or announcement pulse. 
         [0043]    In the case of this modification of the method, just one transformer TR 1  is required, which means that the chip area required for implementing the transfer link and the associated transmitter and receiver circuits is reduced by up to 50% as compared with the method with two transfer channels.