GB2098340A

GB2098340A - Hall effect devices

Info

Publication number: GB2098340A
Application number: GB8210451A
Authority: GB
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1981-05-08
Filing date: 1982-04-08
Publication date: 1982-11-17
Also published as: GB2098340B

Abstract

In an arrangement incorporating a Hall effect device 1, compensation for the temperature dependent offset voltage caused by misalignment of the output leads with respect to the equipotentials within the device is effected by controlling the output in dependence on a signal representative of the impedance presented by the device to the bias current supplied by a constant current source 3 to the device 1. The controlling signal is suitably a signal representative of the voltage drop produced across the device by the bias current. <IMAGE>

Description

SPECIFICATION Hall effect devices This invention relates to Hall effect devices.

A Hall effect device produces an output voltage which is a function of an applied magnetic field and a biassing current.

Due to manufacturing imperfections a Halleffect device normally produces an offset voltage at its output which is strongly temperature dependent. Thus the output of a Hall effect device is subject to variation with temperature even when provided with a constant biassing current and applied magnetic field.

It is an object of the present invention to provide an arrangement incorporating a Hall effect device employing a novel method of compensation for this temperature dependent offset voltage.

According to the present invention an arrangement incorporating a Hall effect device includes: means for applying a substantially constant biassing current to the device; means for deriving a first signal representative of the output voltage of the device; means for deriving a second signal representative of the impedance presented by the device to said biassing current; and compensating means for utilising said second signal to compensate for variations in the first signal with temperature.

The invention resides in the appreciation by the inventors that the offset voltage is due to misalignment during manufacture of the output leads to the Hall effect device with respect to the equipotentials within the device, and that the variation of the offset voltage of a Hall effect device with temperature is due to variation with temperature of the impedance of the material of which the device consists.

Preferably an arrangement in accordance with the invention also includes means for reducing the offset in said first signal with zero applied magnetic field towards zero.

Said second signal is suitably a signal representative of the voltage drop produced across the device by the biassing current.

One arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a block schematic diagram of the arrangement; and Figure 2 is a graph illustrating the variation of offset voltage with temperature for a typical Hall effect device suitable for use in the arrangement.

Referring to Figure 1, the arrangement includes a Hall effect device 1 provided with a constant biassing current from a constant current source 3.

The output voltage of the device 1 is applied to the input of an amplifier Al whose output is applied in one input of a summing circuit 5.

The voltage drop produced across the device 1 by the biassing current is applied to one input of a second summing circuit 7 to whose other input is applied an adjustable stable voltage from a source 9.

The output of the summing circuit is applied to an amplifier A2 whose output is applied to the other input of the summing circuit 5.

The output of the summing circuit 5 is applied to one input of a third summing circuit 11 to whose other input is applied an adjustable stable voltage from a source 13.

The output of the summing circuit 11 is fed to an amplifier A3 whose output voltage constitutes the output of the arrangement.

The output of the arrangement is required to be a temperature independent voltage whose value is proportional to the density of a magnetic field applied to the Hall effect device in operation. To this end, in the absence of an applied magnetic field the value of the voltage of the source 9 is set so that at or near the lowest temperature at which the arrangement is required to operate the output of the amplifier A2 is zero. At the same temperature the value of the voltage of the source 13 is then set so that the output of the amplifier A3 is zero. At or near the highest temperature at which the arrangement is required to operate the gain of the amplifier A2 is then set so that the output of the amplifier A3 again becomes zero.

It can readily be shown that the ratio of the gain of the amplifier A2 to the gain of the amplifier Al is then equal to the ratio of the change in the offset voltage to the change in the total potential drop across the device between any two temperatures.

Thus the source 9 and the gain of amplifier A2 are set to remove the temperature variable component of the device offset voltage and the source 1 3 is set to remove the resulting standing offset voltage.

It will be appreciated that in a practical embodiment of the arrangement the amplifiers A2 and A3 and their associated summing circuits 5 and 7 and 11 will comprise summing amplifiers.

It will further be understood that the amplifiers Al, A2 and A3 are required to have low temperature coefficients, and in this connection it is desirable for amplifiers Al, A2 and A3 to be provided with offset-voltage nulling arrangements.

In an alternative arrangement in accordance with the invention, the amplifier A2 and its associated summing circuit 7 may be replaced by a resistive network. However, amplifiers Al and A3 will normally still be required to obtain an adequate output voltage and impedance.

An arrangement in accordance with the invention finds particular application with Hall effect devices of the kind having a relatively high bulk resistance and low operating current, e.g.

500 ohms and 5 milliamps, wherein change of offset voltage with temperature is relatively high.

Figure 2 illustrates the variation of offset voltage with temperature of one such device.

It will be seen that this device, as do most Hall effect devices, has a linear offset voltage/temperature characteristic so that, in the arrangement of Figure 1, the amplifier A2 is normally required to have a linear input/output characteristic.

One particular application envisaged for an arrangement in accordance with the invention is in a non-contacting ammeter, the Hall-effect device being subjected to the magnetic field produced by the current in a conductor in which current is to be measured, and the output of the arrangement being used to operate an indicating instrument e.g. a moving coil meter.

Claims

1. An arrangement incorporating a Hall effect device including: means for applying a substantially constant biassing current to the device; means for deriving a first signal representative of the output voltage of the device; means for deriving a second signal representative of the impedance presented by the device to said biassing current; and compensating means for utilising said second signal to compensate for variations in the first signal with temperature.

2. An arrangement according to Claim 1 in which said second signal is a signal representative of the voltage drop produced across the device by the biassing current.

3. An arrangement according to either one of the preceding claims further including means for reducing the offset in said first signal with zero applied magnetic field towards zero.

4. An arrangement according to either Claim 2 or Claim 3 in which said compensating means comprises: a first summing circuit whose inputs are said second signal, and a voltage from a first adjustable voltage source; an adjustable gain circuit to which the output of said first summing circuit is applied; and a second summing circuit whose inputs are said first signal, and the output from said adjustable gain circuit.

5. An arrangement according to Claim 4 when dependent on Claim 3 including a third summing circuit whose inputs are the output from said second summing circuit, and a voltage from a second adjustable voltage source.

6. An arrangement according to Claim 4 or Claim 5 in which said adjustable gain circuit comprises a first amplifier.

7. An arrangement according to Claim 6 in which said first amplifier has a linear input/output characteristic.

8. An arrangement according to Claim 4 or Claim 5 in which said summing circuit and said adjustable gain circuit are constituted by a resistive network.

9. An arrangement according to any one of Claims 4 to 8 in which said first signal is applied to said second summing circuit by way of a second amplifier.

10. An arrangement according to Claim 9 in which said second amplifier is provided with an amplifier offset-voltage nulling arrangement.

11. An arrangement incorporating a Hall effect device substantially as hereinbefore described with reference to the accompanying drawings.

12. A non-contacting ammeter including an arrangement according to any one of the preceding claims for producing an output signal representative of a current when the Hall effect device is subjected to the magnetic field produced by said current.