Pulse or digital communications – Cable systems and components
Patent
1993-07-28
1996-08-13
Chin, Stephen
Pulse or digital communications
Cable systems and components
375258, 375319, H04B 300, H04L 2500
Patent
active
055464190
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a bus coupler which operates with a transformer and with a comparator that is connected downstream in a signal-processing branch.
Such a bus coupler is disclosed (FR-A-2,443,770, FIG. 1). The bus coupler of the comparator operates there with a statically set threshold. This data bus system operates with a terminating impedance at the end of each bus line.
In the case of data bus systems, it is known to pass both data and information signals together with a supply voltage on a bus conductor. Such a system is disclosed in EP-A-0,365,696. In this case, the bus conductor is supplied from a voltage supply having a DC voltage which is balanced with respect to ground. A plurality of subscribers can be connected to the bus conductor. Those subscribers can pick off both the supply voltage and an information signal. Information signals can also be transmitted to the bus by the subscribers. A transformer with a capacitor is used for separating received information signals or for emitting information signals to the bus. In the case of such an inductive bus coupler, the capacitor separates the potentials of the energy supply for the on-board network and closes the signal path through the transformer winding on the bus side. The system operates without any terminating impedance at the end of the bus line.
For transmission of bit pulses, the inductance L of the coupler should be as large as possible, since the load of a transmitter which operates on the bus comprises a very large number of parallel-connected stations, each with their own bus coupler. At the same time, the total load impedance should be as low as possible, so that the magnetization current surge is not too large. If a comparator is used in the signal-processing branch of a bus coupler, relatively powerful signals, such as those from transmitters operating close to the bus, should, on the other hand, be received and even powerful interference signals should be attenuated or suppressed.
SUMMARY OF THE INVENTION
The present invention provides a bus coupler which attenuates relatively powerful signals more severely than weak signals.
A bus coupler according to the present invention has a comparator connected downstream in the signal processing branch. The comparator threshold is raised as a function of the signal in the case of large signals relative to small signals. A capacitor which is connected in series with and upstream of the comparator input and a resistance branch which is in parallel with the capacitor are suitable for this purpose, for example. In the case of a positive signal which is received at the capacitor, on its other side, a correspondingly negative signal is supplied to the comparator input, so that only a comparatively large positive pulse could reproduce the old signal state at the output of the comparator. In other words, the threshold value of the comparator is raised, as a result of which a greater attenuation effect is achieved for powerful pulses.
The present invention also promotes the demagnetization of the transformer by compensating pulses, as is known per se from EP-A-0,379,902, but in this case ensures that the demagnetization can take place in a manner which is attenuated as little as possible. In this instance the bus coupler may include a resistance branch that is partially bridged by a valve. The valve is designed to have an open path for a working pulse. The path is interrupted for a compensating pulse. The valve may have a response voltage such that the valve is blocked for small signals. Of course, the valve could be replaced with multiple valves. In consequence, contradictory requirements are satisfied.
According to this, as initially stated, the inductance of the transformer is kept large and, on the other hand, the resistance in the resistance branch is kept small. Furthermore, the demagnetization during the output signal following the information signal, in order to demagnetize the transformer, is provided by an inductance which is reduced by the capac
REFERENCES:
patent: 3638183 (1972-01-01), Progler et al.
patent: 4646319 (1987-02-01), Engel et al.
patent: 4697275 (1987-09-01), Lane
patent: 5091920 (1992-02-01), Ikeda et al.
patent: 5142554 (1992-08-01), Stribling et al.
Chin Stephen
Siemens Aktiengesellschuft
Vo Don
LandOfFree
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