Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
1999-10-28
2001-07-24
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S093800
Reexamination Certificate
active
06266221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a process-independent thermal protection circuit for microelectronic circuits.
2. Description of Related Art
It is known that microelectronic circuits are provided with thermal protection in order to protect their operation if the temperature rises above a predetermined threshold temperature.
These thermal protection circuits generally use the temperature-dependent variation of an implantation resistor, coupled to the variation of a voltage between the base and the emitter of a bipolar transistor.
The coupling can be direct, i.e., the resistor is connected between the base and the emitter of the bipolar transistor.
FIG. 1
illustrates a direct coupling configuration, in which resistor RT is the resistor coupled between the base and the emitter of the bipolar transistor
1
.
FIG. 2
shows an example of an indirect coupling configuration, in which a comparator
2
detects the positive variation of the voltage on one side caused by the resistor RT, and the negative variation on the other side caused by one or more diodes
3
and
4
.
Usually, especially in processes with high production capacities, control of process-related characteristics is unreliable, resulting in the resistance of resistor RT varying considerably between different batches and throughout the years of product production. Statistical estimates confirm resistance variations on the order of plus or minus 10%.
Moreover, two or three tests with different contacts are usually performed in order to calibrate a thermal protection. These tests slow the development of the device, especially when this is done by using lines which are not dedicated to development.
SUMMARY OF THE PRESENT INVENTION
The aim of the present invention is to provide a thermal protection circuit for microelectronic circuits which is substantially process-independent.
Within the scope of this aim, a preferred embodiment the present invention is a thermal protection circuit for microelectronic circuits which substantially completely eliminates the uncertainty of process-dependent variations in a temperature sensing resistor.
The preferred embodiment of the present invention allows for the simple selection of a triggering temperature level.
The preferred embodiment of the present invention is highly reliable and relatively easy to produce at competitive costs.
This aim and others which will become apparent hereinafter are achieved by a process-independent thermal protection circuit for microelectronic circuits, characterized in part by including a thermal ramp generator suitable to generate a first thermal ramp signal and a second thermal ramp signal, a differentiator suitable to determine the difference between the first and second thermal ramp signals in order to emit a difference voltage signal, and a comparator suitable to compare the difference voltage signal with a reference voltage signal in order to activate a thermal protection signal when the difference voltage signal drops below the reference voltage signal.
REFERENCES:
patent: 5563760 (1996-10-01), Lowis et al.
patent: 5638246 (1997-06-01), Sakamoto et al.
patent: 5642252 (1997-06-01), Sakamoto et al.
Jenkens & Gilchrist P.C.
Sherry Michael J.
STMicroelectronics S.r.l.
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