Miscellaneous active electrical nonlinear devices – circuits – and – External effect – Temperature
Reexamination Certificate
1999-09-09
2001-07-03
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
External effect
Temperature
C327S080000
Reexamination Certificate
active
06255892
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention pertains to a temperature sensor for measuring temperatures within a defined temperature measuring range. The sensor has the following features:
a reference voltage source for providing a reference voltage at an output terminal which is connected to a first input terminal of a comparator;
a series circuit of a measuring element and a reference component connected between a first and a second supply terminal, whereby a temperature-dependent voltage is applied to a node common to the semiconductor component and the reference component and is applied to a second input terminal of the comparator.
Such kinds of temperature sensors, in particular those fabricated in an integrated way, are used for switching, especially for switching off loads if a specified temperature is exceeded. For this purpose the temperature-dependent voltage and the reference voltage are compared through a comparing element usually realized as a comparator, whereby one of two different voltage levels is applied to the output of the comparator depending on whether or not the temperature-dependent voltage is higher than the reference voltage.
A temperature sensor of this kind is known from the commonly assigned invention described in German published patent application DE 44 37 461 A1. The reference voltage source is thereby formed as a series circuit between a first supply terminal and a second supply terminal. The series circuit has a depletion-mode FET wired up as a current source and an enhancement-mode FET wired up as a diode. A node common to the depletion-mode FET and the enhancement-mode FET is thereby connected as the reference voltage output to a first input terminal of the comparator. The two transistors in that prior art temperature sensor are dimensioned such that the reference voltage remains constant within the temperature range to be measured, or increases with increasing temperature. The reference component in the known temperature sensor is realized as a depletion-mode FET which is wired up as a current source. The measuring element connected in series with the reference component has a temperature-dependent current characteristic and is formed as a series circuit of two enhancement-mode FETS, each of which is wired up as a diode. A node common to the depletion-mode FET and the series circuit of the enhancement-mode FET is connected to a second input of the comparator, whereby the depletion-mode FET serving as reference component and the enhancement-mode FET connected in series thereto are tuned to each other such that the potential applied to this node decreases with increasing temperature in order to cause a change of the voltage level at the output of the comparator in the event that this potential falls below the reference voltage delivered by the reference voltage source.
In the prior art temperature sensor, the switching temperature, i.e. the temperature at which the temperature-dependent voltage attains the value of the reference voltage, is defined exclusively through the dimensioning of the components.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a temperature sensor, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a switching temperature that is adjustable.
With the foregoing and other objects in view there is provided, in accordance with the invention, a temperature sensor for measuring temperatures within a defined temperature measuring range, comprising:
a reference voltage source with an output terminal receiving a reference voltage;
a comparing element with a first input terminal connected to the reference voltage source, and a second input terminal;
first and second supply terminals carrying a supply voltage adjustable within a defined supply voltage range;
a series circuit of a measuring element and a reference component connected between the first and second supply terminals, whereby a node common to the measuring element and the reference component receives a temperature-dependent voltage and is connected with the second input terminal of the comparing element; and
the reference component having a voltage-dependent current characteristic within a voltage range of a voltage across the reference component determined by the defined supply voltage range.
In other words, the objects of the invention are satisfied in that the supply voltage applied between the supply terminals is adjustable within a defined range and the reference component has a voltage-dependent current characteristic within a voltage range of a voltage arising across the reference component as a result of the above adjustable supply voltage. The reference component delivers to the semiconductor component a current that is dependent on this voltage.
If the supply voltage at the temperature sensor according to the invention changes, a voltage arising across the reference component also changes, causing a change in the current flow through the reference component as a result of the voltage-dependent current characteristic of the reference component. This change in the current through the reference component causes a change in the voltage across the semiconductor component connected in series to the reference component and with temperature-dependent current characteristic, and thereby at the node common to the reference component and the semiconductor component. The voltage applied to this common node is therefore dependent on the supply current as well as on the temperature. As a result there are different temperatures for different values of the supply voltage, at which temperatures the voltage at the common node between the semiconductor component and the reference component, or at the second input terminal of the comparator, exceeds or is smaller than the value of the reference voltage supplied by the reference voltage source. In this respect the reference voltage source is preferably dimensioned such that it supplies a constant reference voltage both over the temperature measurement range and over the supply voltage range. The switching temperatures for the temperature sensor according to the invention are thus dependent on the supply voltage as well as on the dimensioning of the components used.
In accordance with an added feature of the invention, the reference component is an ohmic resistor.
In accordance with an additional feature of the invention, the reference component is a thick oxide depletion-mode transistor.
For both ohmic resistors and so-called thick oxide depletion-mode transistors the current flowing through the component increases with the voltage applied across the component. In the case of ohmic resistors this applies for almost any voltage and the thick oxide depletion-mode transistors for use in the temperature sensor according to the invention are so dimensioned that their drain current within the variable supply voltage range is voltage-dependent and, in particular, increases with increasing supply voltage.
In accordance with another feature of the invention, the semiconductor component with the temperature-dependent current characteristic is a diode.
In a preferred embodiment of the invention, the diode is a MOS diode, i.e. it is a MOS transistor wired up as a diode.
In accordance with a further feature of the invention, the measuring element is a series circuit of at least two MOS transistors each wired up as a diode.
In this context, the term “temperature-dependent current characteristic” means that for a specific voltage applied across the component the current flowing through the component depends on the temperature.
In accordance with again an added feature of the invention, a reference voltage at the output terminal of the reference voltage source is temperature-independent within the temperature measuring range and is independent of the supply voltage within the defined supply voltage range.
In accordance with again another feature of the invention, the reference voltage source is connected b
Gärtner Manuel
Hertrich Helmut
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Zweizig Jeffrey
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