Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons
Patent
1988-11-23
1990-12-11
Miller, Stanley D.
Electrical transmission or interconnection systems
Nonlinear reactor systems
Parametrons
307443, 307544, H03K 500
Patent
active
049773402
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a device for protecting input signals of an electrical circuit against interference pulses of a higher frequency.
Such a device is also known from the DE-PS No. 28 32 766. DE-OS No. 2832766 discloses a protection device comprising a capacitor which substantially determines the time constant of a low-pass filter which acts against higher-frequency interference signals or interference pulses. The low-pass filter substantially comprises a transistor which is switched via the capacitor into its conductive state when an interference pulse occurs and accordingly loads the source of interference at a low impedance. Low-frequency signals do not lead to an actuating of the transistor, so the overall arrangement acts like a low-pass filter.
A substantial disadvantage of this known protection device consists in that a very large capacitor is required, which does not readily permit a monolithic integration of the protection device, because the capacitors which can be realized in integrated circuits at a reasonable expense are in the order of magnitude of 100 pF. Moreover, currents can only be realized reasonably down to the order of magnitude of 0.5 uA. For even smaller currents, the limit is set by blocking currents, which sharply increase at high temperatures in particular. In practice, therefore a limit is set for the realization of integrated low-pass filters in monolithic integration technology. After this limit, one must work with a large capacitor which is to be connected from the outside to the remaining integrated portion of the protection device for reasons relating to costs and layout.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an electric circuit comprising a protection device for protection against interference signals, which protection device can be completely monolithically integrated at a reasonable expense and which, nevertheless, performs a high filtering action against interference signals.
This object is met by the provision of a protecting device which includes a power source, an emitter follower connected to the power source and including a transistor whose collector-emitter path is connected in series with a first current source and whose base is connected to a source of the input signals, a low-pass member including a series connection of a second current source and a capacitor, the series connection being connected to the power-source, and the junction point of the capacitor with the second current source being connected via a diode to the first current source and to the input of a Schmitt-trigger circuit. The output of the Schmitt-trigger is connected to an input of the electric circuit.
The electrical circuit according to the present invention has the particular advantage that it requires a particularly low expenditure on structural component elements. Accordingly, the integration is particularly inexpensive, since the integrated protection device requires very little surface area. Moreover, the protection device, according to the invention, has a particularly high resistance to temperature changes. The monolithic integration construction provides a virtually ideal synchronizing for the emitter follower and the diode, so that very few errors occur during the transmission of a constant-voltage level.
BRIEF DESCRIPTION OF THE DRAWING
The invention both as to its construction so to its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of the preferred embodiments with reference to the accompanying drawings wherein:
FIG. 1 shows a basic circuit diagram of a protection device, according to the invention, which is series connected with an input of a subsequent electric circuit arrangement;
FIG. 2 shows a particularly simple embodiment of a protection device according to the invention which is suitable for a completely monolithic integration;
FIG. 3 shows a modification of the capacitive means of FIG. 1 for increasi
REFERENCES:
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patent: 4287435 (1981-09-01), Cavaliere et al.
patent: 4289978 (1981-09-01), Konian et al.
patent: 4339669 (1982-07-01), Jarrett et al.
patent: 4518878 (1985-05-01), Moulding
patent: 4890015 (1989-12-01), Wise
Kohl Walter
Nagel Karl
Cunningham T.
Miller Stanley D.
Robert & Bosch GmbH
Striker Michael J.
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