Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons
Patent
1992-05-05
1994-04-19
Sikes, William L.
Electrical transmission or interconnection systems
Nonlinear reactor systems
Parametrons
307310, 323231, 323317, H03K 326, G11C 1100
Patent
active
053048610
DESCRIPTION:
BRIEF SUMMARY
An object of the present invention is a circuit for the detection of temperature threshold, light and unduly low clock frequency, that can be used in all the fields where such checks have to be conducted. The invention can be used especially in the field of integrated circuits and in the field of circuits for chip cards or memory cards.
It is known that the temperature of electronic integrated circuits, such as chip cards, memory cards or other programmable circuits, increases during their operation and, especially, during their programming. Two temperature thresholds are observed, a first threshold beyond which the circuit no longer works normally but returns to its normal operation if its temperature falls back below this threshold, and a second one for which there is a breakdown of the integrated circuit.
It is thus seen that if the rate of programming is excessively high, the temperature of the circuit will increase greatly, prompting either an erroneous programming or, at worst, the destruction of the circuit. It may be pointed out that fraudulent individuals could be tempted to raise the temperature of the integrated circuit to a temperature above the operating limit, causing either false programming or a modification of the memory content.
A circuit for the detection of the first temperature threshold gives a binary signal that can be used, for example, for the checking of access to the circuit: it is then possible to prohibit the operation of the circuit for a temperature above this first temperature threshold.
There are known temperature detectors based on integrated circuits that comprise chiefly a forward-biased MOS transistor and have a conduction threshold known to vary with the temperature by about 2 mv/.degree. C. This detector is not very sensitive since a high variation in temperature prompts only a small variation in voltage. Moreover, it is not very reliable since it is known that the threshold voltage cannot be reproduced with precision from one integrated circuit to another, owing to differences in concentration of impurities.
There are other known detectors that essentially use a MOS transistor reverse biased by an electrical supply, the current of which is known to vary substantially with the temperature: for example, the current may increase twofold for an increase of about ten degrees in temperature, rector such as this is described, for example, in French application No. 87 12070 filed on 31 Aug. 31, 1987.
However, in a detector such as this, the current depends on the level of the supply voltage. Now, this level varies typically between 4.5 and 5.5 volts for a nominal level of 5 volts: this is an intrinsic feature of the supply circuits used. Furthermore external disturbances, notably those applied by fraudulent individuals, may also cause variations in the level of the supply.
The variation in current induced by the variation in the level of the supply voltage will prompt the triggering of the detector for a voltage below or above the threshold voltage of the circuit to be detected. In the former case, there is a false alarm that only hampers the use of the circuit, for example in slowing down the access time. In the latter case, the use of the circuit is authorized beyond its threshold temperature: the detector no longer fulfils its function. It can therefore not be used as such.
The invention overcomes this drawback by proposing the implementation of another known physical phenomenon. It is known that the current in a reverse-biased diode increases significantly with the temperature: the current typically doubles every 10.degree. C. for silicon. It is shown that, from a certain temperature onwards, the increase becomes greater. The current due to the minority carriers (reverse current of saturation) which, until then, has been predominant, becomes smaller than the current due to the majority carriers (diffusion current). Moreover, the temperature thus defined is in fact the temperature from which the circuit into which the diode is integrated begins to stop working normally: t
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Fruhauf Serge
Martin Michel
O'Malley Paul W.
SGS-Thomson Microelectronics S.A.
Sikes William L.
Tran Toan
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