Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
2000-07-15
2003-11-04
Jackson, Stephen W (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C361S058000, C361S078000
Reexamination Certificate
active
06643111
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electronic transducer device, and in particular to an electronic transducer device that includes overvoltage protection to protect the device from excessive supply voltage values.
Transducer devices often contain a sensor to measure an external state. The measured external state is conducted as an electrical signal to a signal detection device. Such transducers are often exposed to interference from breaks in the supply lines, especially a break of the ground conductor. Such breaks must be detected in many cases by the signal detection device to ensure that the value is not interpreted erroneously as a valid measured transducer signal.
Such transducer devices are used, for example, as substitutes for potentiometer arrangements, wherein the current position of a mechanical positioning device is queried by an electronic processing device (e.g., a processor). Broad applications are found, for example, in motor vehicles, when the positions of motor control equipment, brakes, headlights, seats, etc. are to be evaluated or stored. Since mechanical wear on such potentiometer arrangements eventually can result in faulty measurements or even in operational failures, contact-free measurement methods, which use sensors to detect the particular position, find increasing application. A similar application of such transducer devices concerns the measurement and transmission of temperature, pressure, moisture, brightness, and other physical quantities through appropriate sensors.
German patent application DE 197 51 519 A1, for example, describes a transducer device with a Hall sensor for a linear sensor, comprising two mechanical parts which can move relative to one another, and whose relative position is measured by the transducer device. The transducer device contains a fault alarm circuit that emits a defined voltage signal if the grounding conductor is interrupted. In applications intended for motor vehicles, one of the three connecting lines of the transducer device can easily be disconnected because the linear sensor is subject to severe vibrations, and three connecting lines connect the transducer device to a plug connector on the linear sensor, from which plug connector three conductors then go to the evaluation and supply circuit. The fault alarm circuit contains an n-channel-depletion-MOS-field effect transistor, which is connected between the positive operating voltage line and the output line of the transducer device. In the normal operating state—that is without any line breaks—a DC converter fed from the operating voltage sets the gate electrode of the depletion transistor to a sufficiently low potential so that the depletion transistor is blocked. For example, the gate potential lies 1 V below the ground potential. If the ground conductor is disconnected, the DC converter ceases to function, and its output voltage thus corresponds to the operating voltage. Thus the depletion transistor becomes fully conducting, so that it raises the potential of the output line approximately to the operating voltage, and this is recognized by the signal detection device as a faulty signal. A break in the operating voltage line is less critical, because in this case the transducer output assumes ground potential, which the receiving side easily recognizes as a faulty signal. It is further specified that the entire transducer device with its fault alarm circuit can also be integrated as a microelectronic switching circuit and that this represents a preferred embodiment.
Commonly assigned European patent application EP 0 648 019 A2 describes a monolithically integrated voltage regulator in CMOS technology. To protect against wrong poling, it contains an MOS transistor structure, connected in series with the voltage regulator. In the event of wrong poling, this MOS transistor structure reduces the resulting mis-poling current to such an extent that destruction of the monolithically integrated circuit is prevented. Furthermore, the described embodiment also contains circuit measures to enable operation from a supply voltage which is higher than would be permissible according to the basic production standard, for example a standardized CMOS technology.
There is a need for an electronic transducer device that includes the ability to detect a break in a power supply line.
SUMMARY OF THE INVENTION
It is an object of the invention to adapt the known transducer device to a standardized production process for monolithically integrated circuits, especially a CMOS production process. An additional object is to take precautions to prevent destruction of the monolithically integrated circuit when an overvoltage is applied and/or when the poling of the connections is reversed.
A monolithically integrated transducer device includes a p-channel-depletion-transistor, controlled by a charge pump and situated in its own n-well between the operating voltage connection and the signal output. Under normal operation, when the operating voltage and the ground potential are present at the transducer device and thus at the charge pump, this transistor is blocked; when the ground conductor is disconnected, this transistor becomes conducting. The n-well in the p-conducting substrate is connected to the operating voltage connection via a co-integrated resistor. The charge pump and the depletion transistor form the fault alarm circuit. Using the p-channel-depletion-transistor in its own well achieves the result that this transistor can be blocked with a positive voltage and thus all voltages are higher than the potential at the substrate of the monolithically integrated circuit.
When converting the transducer device into a monolithically integrated circuit, care must be taken to protect the transducer device against interchange of the connections when the operating voltage is applied. Through a wrongly applied operating voltage, zones in the: monolithically integrated circuit which are otherwise blocked are brought into the forward conducting state, which can sometimes cause a high current flow, which finally results in destruction of the component. To achieve this intended protection against an interchange of the connections of the operating voltage, the invention specifies that the n-well of the MOS-depletion-transistor is connected to the operating voltage, not directly as usual, but via a co-integrated resistor. A current which flows through the well in the event of mis-poling, is thus limited at least by this resistor. The depletion transistor, situated between the operating voltage connection and the signal output, is thus also protected against accidental application of the operating voltage to the signal output.
To detect a break in the operating voltage line on the receiver side, a further development of the invention specifies that the signal output of the transducer device and/or the signal input of the receiving device is connected to ground potential via a co-integrated or external resistor, which pulls the signal output quickly to ground potential, independently of parasitic currents or capacitances. The resistor to ground at the signal input of the receiving device is used to facilitate detection of a break in the external signal line. The resistors to ground here have a much higher ohm resistance than the internal resistance of the transducer device.
If the operating voltage is higher than the maximum voltage prescribed for the particular circuit technology, that is also in the case of brief overvoltages, which can occur, for example, during operation in a motor vehicle, the depletion transistor should be protected against excessive voltages. For this purpose, a preferred further development of the invention specifies that the excessive voltage is divided among two series-connected p-channel-depletion-transistors. In normal operation, one of these is in the blocked state and the other is connected as a cascode transistor and thus is conducting. Its gate is controlled through a driver circuit which generates the cascode control voltage. The output voltage
Motz Mario
Theus Ulrich
Jackson Stephen W
Micronas GmbH
Samuels , Gauthier & Stevens, LLP
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