Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion
Reexamination Certificate
1999-03-12
2001-10-02
Young, Brian (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Analog to digital conversion
C375S213000, C341S118000
Reexamination Certificate
active
06297761
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a measuring apparatus for digitally detecting analog measured variables.
Most currently known sensor elements supply the result of a measurement in the form of an analog variable. By contrast, further processing of the signals is nowadays preferably digital, so that an analog/digital conversion facility needs to be provided within the signal chain. Hence, particularly when microcomputers or microcontrollers are used for further digital signal processing, analog/digital converters are usually connected between the sensor element and the microcomputer/microcontroller. When this is done, the additionally required circuit complexity rises in proportion to the accuracy demanded for the conversion. This complexity is regarded as being too high for numerous applications.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a measuring apparatus for digitally detecting analog measured variables that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has a lower level of complexity for the same accuracy.
With the foregoing and other objects in view there is provided, in accordance with the invention, a measuring apparatus, including: a sensor element producing a sensor output signal proportional to a variable to be measured; an integrator connected to the sensor element that, beginning at a starting value, integrates the sensor output signal from the sensor element and outputs an integrator output signal; a comparator connected downstream of the integrator, the comparator comparing the integrator output signal with a threshold value and outputs a compartor output signal corresponding to a result of the comparison; and a reset device connected downstream of the comparator and resetting the integrator to the starting value at specific times.
The measuring apparatus according to the invention contains a sensor element, an integrator, a comparator and a reset device. In the apparatus, the sensor element produces a current that is proportional to a variable to be measured. The current is integrated by the integrator, beginning at the starting value. The comparator connected downstream of the integrator compares the output signal from the integrator with a threshold value and outputs an output signal corresponding to the result of the comparison. The reset device connected downstream of the comparator resets the integrator to the starting value at specified times. In this case, the starting value can be any desired value between zero and the threshold value, including zero itself. If the threshold value is exceeded inside a fixed time window between two reset instants, this indicates that a specified measured value has been exceeded.
In a development of the invention, a time measuring device downstream of the comparator measures the time duration between the starting value being exceeded and the threshold value being reached and outputs a signal corresponding to the time duration as a measure of the measured value obtained at the sensor element. Therefore, the exact measured value can now be determined.
The instant at which the integrator is reset to the starting value can either occur at fixed regular time intervals, or else whenever the threshold value has been exceeded. Which of these two possibilities is used in any given case depends on the respective application.
The integrator is preferably formed by an individual capacitor, the voltage present across the capacitor corresponding to the integral of the output current from the sensor element. It is therefore advantageous to use only a single capacitor, because the passive configuration produces no additional interference noise or offsets and, furthermore, the circuit complexity is extremely low.
In this configuration, a resistor may be connected upstream of the capacitor, i.e. the current from the sensor element is passed to the capacitor via the resistor. In this case, the resistor is used for current limiting and thus for protecting the sensor element and the capacitor in the event of faults occurring, for example.
The capacitor is preferably discharged through a reset device having a controlled switch which is switched on by the comparator if the threshold value at the output of the comparator is exceeded and thus connects the capacitor to a reference voltage source governing the starting value. In this case, the reference voltage is connected to the capacitor and thus defines the starting value.
The time measuring device preferably has a counter that is connected downstream of a reference clock source and is controlled by the comparator. In this way, a time measuring device having a high level of accuracy can be produced with a low level of circuit complexity.
The sensor element provided is, in particular, a reverse-biased pn semiconductor junction whose reverse current is exponentially dependent on the temperature at the semiconductor junction. As a current is output directly, no additional circuitry is necessary. The pn semiconductor junction may be a diode or a transistor wired up accordingly, for example. Furthermore, instead of a semiconductor junction for measuring temperature, it is also possible to use a photosensitive semiconductor junction for measuring light in the same way. Other sensors which output a current or use special converter circuits connected downstream to output a current proportional to the measured variable are also suitable in the same way.
The comparator and/or the time measuring device and/or the reset device are preferably configured such that they are also integrated in a microcomputer or microcontroller or that devices already present in them are used appropriately. Under certain circumstances, this enables the additionally required external complexity to be reduced to the sensor element itself and a capacitor.
The measuring apparatus according to the invention is particularly suitable for measuring the silicon temperature of semiconductors and, in particular, of power semiconductors. In this case, a diode is also integrated into the transistor or into the chip and thus detects the temperature of the silicon exactly. If reverse-biased, the reverse current in the diode changes exponentially with temperature. This exponential characteristic allows broad temperature ranges to be determined, even with manufacturing tolerances.
According to the invention, the silicon temperature is detected using temperature/time conversion. The reverse current supplied by the integrated diode (or other pn junction) feeds a temperature-dependent current to a capacitor. The integrating behavior of the capacitor results in achieving effective interference suppression at the same time. The reverse current supplied determines the rise in the voltage across the capacitor, so that sooner or later the threshold value is reached.
In this configuration, the voltage across the capacitor is monitored by the comparator. The interrupt input of a microcomputer/microcontroller may also be used as a comparator in the same way. Furthermore, the capture capability of the microcomputer/microcontroller allows measurement of the time elapsing between the capacitance being discharged and the threshold value being reached. In this case, the capacitor can in each case be discharged after the threshold value has been reached, or else cyclically. With cyclic discharging, it is also possible to produce a simple overheating protection facility in that an interrupt is output as soon as the threshold value is reached. In this case, the discharging period must be the same as the time corresponding to the desired turn-off temperature. In this mode of operation (overtemperature protection), cyclic discharging takes place, after appropriate initialization of the timer, without burdening the central processor unit at all. The microcomputer/microcontroller is burdened slightly only by the interrupt responding to the threshold value being reached. The microcomputer/microcontroller can then turn off the correspo
Amann Heinz
Barrenscheen Jens
Jansen Andreas
Kern Hermann
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Nguyen John
Stemer Werner H.
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