Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Converting input voltage to output current or vice versa
Reexamination Certificate
1999-11-17
2001-10-02
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Converting input voltage to output current or vice versa
C327S510000
Reexamination Certificate
active
06297673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an evaluation circuit for electronic signal transducers with current interfaces, which includes a component for converting a signal from a transducer into a signal voltage.
2. Prior Art
An evaluation circuit of this kind is particularly used with actuators and sensors which emit a current as an output signal. An evaluation circuit of this kind is frequently used in sensors which are used to detect the speed of motor vehicle wheels for evaluation in antilock control devices. In this connection, the sensor output signal oscillates between two current values depending on the signal state. Usual values of the signal current are, for example, 10 milliamperes for a low signal level and 20 milliamperes for a high signal level.
In order to convert the signal current into a signal voltage that can be evaluated by means of comparators, for example, the current is conducted through a measuring resistor. The measuring resistor is connected in series with the sensor. As a result of the series connection, the voltage that is applied by way of the sensor is reduced by the voltage drop at the measuring resistor. Consequently, a different voltage is applied by way of the sensor depending on the signal state.
Since the measuring resistor is usually dimensioned so that the voltage drop in it is 1.5 to 3 volts, the supply voltage available for the sensor drops by 1.5 to 3 volts. This can impair the function of the sensor. A reduction of the measuring resistor could actually achieve the fact that the supply voltage available for the sensor would no longer have large fluctuations, but a smaller measuring resistor supplies only very small signals. Problems in the evaluation of the signals arise as a result of this. Furthermore, the influence of incorrect couplings and similar malfunctions increases.
Furthermore the measuring resistor must be designed for a relatively high power since the full supply voltage can be connected to it in the event of a malfunction of the sensor or an error in the wiring harness (e.g. a short circuit).
SUMMARY OF THE INVENTION
The object of the invention is to design an evaluation circuit of the type mentioned at the beginning in such a way that the voltage that is applied by way of the sensor has fewer fluctuations.
This object is attained by virtue of the features of the characterizing part of claim
1
. Advantageous improvements of the invention ensue from the dependent claims.
According to the invention the evaluation circuit for an electronic signal transducer comprises
a current interface for supplying a current signal from the electronic signal transducer;
a current-sensing field effect transistor having a gate, a source, a drain and a sensing output, which is connected with the current interface so that a current signal from the transducer passes through the source and drain;
monitoring circuit means for controlling the current-sensing field effect transistor in the event of erroneous operation or malfunction, which has an output terminal connected to the gate of the field effect transistor and an input terminal connected to the source or the drain of the current-sensing field effect transistor;
a current reflector circuit having an input and an output, wherein the input of the current reflector circuit is connected to the sensing output of the current-sensing field effect transistor; and
means for converting current to voltage, preferably a resistor, which is connected to the output of the current reflector circuit, so that the current signal is converted to a voltage signal.
The sensing output of the sensing FET correspondingly supplies the coupling factor of the sensing FET with a current that corresponds to the current flowing by way of the drain-source section. The current emitted by the sensing output of the sensing FET is converted into a voltage in the conversion element. Since this voltage is no longer connected in series with the supply voltage of the sensor, it no longer has repercussions on the sensor.
The sensing output of the sensing FET is advantageously connected to the conversion element by way of a current reflector. This results in a further decoupling of the dropping voltage at the conversion element. The circuit can be dimensioned so that the dropping voltage at the conversion element assumes an optimal value for the further signal processing.
In another embodiment of the invention, a monitoring circuit is provided whose output is connected to the gate connection of the sensing FET. In a particularly advantageous manner, an input of the monitoring circuit is connected to the drain connection of the sensing FET. In the event of a malfunction, the sensing FET can be switched off by the monitoring circuit so that a power loss no longer occurs. As a result of this, the circuit can be designed for very low powers.
By means of the invention, a negligible fluctuation of the supply voltage available for the sensor is achieved in principle so that no direct measuring resistor is used but rather a current-to-current transformation is carried out. This circumvents the problem that a large measuring resistor causes voltage problems and a small measuring resistor does not supply signals that can be evaluated and is disadvantageous with regard to incorrect couplings. A current interface is provided by means of the sensing FET.
REFERENCES:
patent: 5218298 (1993-06-01), Vig
patent: 5446397 (1995-08-01), Yotsuyanagi
patent: 5760614 (1998-06-01), Ooishi et al.
“Designing with SENSFETS”, by Warren Schultz, in Linear Design, PCIM Europe, Nov. 1989, pp. 242 to 248.
Robert & Bosch GmbH
Striker Michael J.
Zweizig Jeffrey
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