Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Parallel controlled paths
Patent
1996-09-20
1998-12-08
Nelms, David C.
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Parallel controlled paths
327 71, 327205, H03K 1762
Patent
active
058475923
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is based on a control circuit having a plurality of sensors producing mutually phase shifted sensor signals. Such a circuit has been disclosed in EP-B1-0 351 697 and, for example, is used for commutation or speed regulation of the capstan motor in a video recorder.
BACKGROUND OF THE INVENTION
Hall elements can be used as sensors for the respective angular position of the rotor. These Hall elements have a large output-voltage range. The output voltage of such an element has interference superimposed on it, however, which is directly magnetically pronounced, inter alia, by the motor coils. Taking account of all the tolerances, such interference is greater than the smallest signal voltage. For this reason, a simple solution, such as filtering out the interference by means of a threshold voltage or hysteresis, cannot be used or can be used only to a limited extent. Even an AGC circuit cannot be used, since the motor must start correctly and immediately from rest. An AGC circuit would need a number of oscillations in the input signal in order to stabilize itself.
SUMMARY OF THE INVENTION
The invention is based on the object of implementing a circuit which is even able to suppress the said interference, and also retains this capability over an unlimited time. When used on a motor, the circuit is also intended to be able to suppress interference when the motor is stationary.
This object is achieved by the invention specified in the independent claims. Advantageous developments of the invention are specified in the subclaims.
The invention is based on the following considerations and knowledge. As is known, the sensor signal which is supplied to the comparator is in the vicinity of 0 at the point in time at which the comparator for a sensor signal in each case responds before a sensor, that is to say its output voltage changes between the two logic values "0" and "1". The invention now makes use of the fact that the sensor signals of the other sensors have a significant amplitude, because of the identical nature and the constant phase shift. For example, in the case of an arrangement having three sensors, the sensor signals of the other sensors will in each case have an amplitude in the region of 86% for a symmetrical rotating field with a 120.degree. offset. The sensor signals of the other sensors are thus in each case used for the change in the hysteresis in the case of the comparator for one sensor signal.
The sensor signals of all the sensors are preferably supplied to an OR stage which responds to the positive and/or negative peak values of the sensor signals and whose output voltage is applied to the inputs of the comparators, which inputs determine the hysteresis. The OR stage thus always supplies the sensor signal having the greatest amplitude in this case.
It is also possible in this arrangement to provide a first OR stage for the positive peak values and a second OR stage for the negative peak values of the sensor signals, and a changeover switch which is controlled by the output voltage of the comparator and switches the input of the comparator over between the outputs of the two OR stages. In consequence, it is possible to achieve hysteresis which is symmetrical with respect to the zero line, and thus improved suppression of the interference.
The sensor signal coming from a sensor and the output voltage of the OR stage are preferably respectively applied to the two inputs of a comparator. In this case, a switch, which is opened and closed alternately by the output voltage of the comparator, is in each case connected between the output of the OR stage and the associated input of the comparator.
In the case of a development of the invention, a second OR stage for a second OR process can also be provided after the said first OR stage. The output voltage of the OR stage of a first polarity and those half-cycles of the output voltages of the sensors which are of the opposite polarity in comparison therewith but have been transferred to the first polarity are now a
REFERENCES:
patent: 4157509 (1979-06-01), Zielinski
patent: 4259662 (1981-03-01), Yoshida
patent: 4268764 (1981-05-01), Eckert
patent: 4283664 (1981-08-01), Ebert
patent: 4354145 (1982-10-01), Janssen
patent: 5107135 (1992-04-01), Hagita
patent: 5182500 (1993-01-01), Shimada
Gleim Gunter
Heizmann Friedrich
Rekia Bernd
Deutsche Thomson-Brandt GmbH
Ho Hoai
Nelms David C.
Tripoli Joseph S.
Wein Frederick A.
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