Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Patent
1995-04-07
1998-09-22
Cunningham, Terry
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
327316, 327327, 326 30, H03K 508
Patent
active
058120076
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
When binary signals, generated by temporarily connecting a DC source at relatively high voltage to a signal line, are used to transmit information over the signal line, the residual charge on the signal line must be reduced as quickly as possible after the signal level changes to achieve a high baud rate for transmission and to detect quickly a signal change. In addition, partial discharges on the signal line must be dissipated quickly. These requirements are especially important for applications in which signals are conducted over a long, capacitance-affected signal line. In such applications, a high discharge current must be assured for the charge stored on the signal line.
For example, if a 220 VDC source is used and the length of the signal line is 1 km, corresponding to a line capacitance of 200 nF, a discharge current of 15 mA must flow if the voltage on the signal line is to be reduced sufficiently within 1 ms after each disconnection of the DC source (from 220 V to 150 V for example). The discharge current must be correspondingly high if a parasitic noise voltage is to be dissipated quickly.
To solve this problem, in a system for transmitting binary signals over a signal line (see e.g., command and alarm module of the previously publicly used Siemens SINAUT-LSA telecontrol unit), a discharge circuit with a resistor and a downstream diode circuit was connected to the signal line. A high discharge current can flow continuously through such a discharge circuit even when the DC source is temporarily connected to the signal line. This results in a power loss of several watts. This power loss can cause problems with heat generation, particularly when several signal lines lead to one unit in which a corresponding number of discharge circuits must be available.
German Patent No. 12 87 604 discusses a system for transmitting binary signals over a signal line to a signal detector, in which a DC source is temporarily connectable to the signal line as binary signals are generated, and in which a discharge circuit is connected to the signal line. In the arrangement of the '604 German patent, to compensate for parasitic line capacitances from the discharge circuit, the charge on the line is reversed between the binary signals formed by positive pulses, with a transistor that is connected so that it usually conducts, being blocked at the beginning of each positive pulse, and conducting again at the end of each pulse. In this way, another transistor is switched to conduct briefly, through which a negative voltage is applied to the line temporarily, resulting in a rapid polarity reversal of the line.
SUMMARY OF THE INVENTION
The goal of the present invention is to reduce considerably the power loss caused by the discharge circuit and to eliminate noise coupled into the signal line during any pauses between the binary signals. The present invention departs from a system for transmitting binary signals over a signal line to a signal detector in which a DC source is temporarily connectable to the signal line as binary signals are generated and a discharge circuit is connected to the signal line.
To achieve the above mentioned goal, in a system of this kind according to the present invention, the discharge circuit contains a switchable current sink connected to the signal line. The discharge circuit has a threshold value determination device connected to the signal line, in parallel with the switchable current sink. The output of the current threshold value determination device is connected with a control input of the switchable current sink such that a current-determining resistance of the switchable current sink is changeable under control by the threshold value determination device.
A threshold value determination device is discussed in German Patent No. 1 237 173. However that device forms a component of a circuit for steepening the slopes of pulses, especially in radar and television technology.
An important advantage of the system according to the present invention is that only a l
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Cunningham Terry
Siemens Aktiengesellschaft
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