Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-02-24
2001-07-24
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S225000
Reexamination Certificate
active
06265864
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a Hall effect sensor. More particularly, the present invention relates to a Hall effect sensor for use in detecting rotational movement. Specifically, the present invention relates to a stabilized Hall effect sensor that efficiently detects the movement of gear teeth mounted on a rotating shaft in an engine or other similar apparatus.
BACKGROUND OF THE INVENTION
Modern machinery often uses sensors to measure the movement of various parts in the machinery. These measurements are used to, inter alia, make adjustments in how various parts of the machinery operate, and hence, improve the performance of the machinery. For example, the precise speed with which a shaft having gear teeth thereon rotates may be critical to the operation of an internal combustion engine. In such a case, sensors that are able to precisely measure the speed at which the shaft rotates can be used to provide information to other parts of the engine. Such information can be used, for example, by the part of the engine which controls the timing for the fuel and the spark to improve the performance of the engine.
Hall effect sensors are a class of sensors that are used to, inter alia, detect the movement of ferrous items. As such, they are well suited to uses such as detecting the rotational movement of a shaft in an engine. Specifically, a Hall sensor incorporates a Hall plate that senses the movement of a ferrous item as it passes by the Hall plate. The Hall plate produces a voltage output between two terminals. This voltage output changes as the ferrous item first approaches and then moves away from the Hall plate. When such a Hall plate is mounted adjacent gear teeth on a rotating shaft, the frequency with which the voltage output from the Hall plate increases and decreases is a precise measurement of the rotational speed of the shaft. This voltage output can then be transformed into a different type of electrical signals which may be used by a microprocessor or other circuitry to control various other parts of the engine, for example, the timing of the fuel or spark.
The ability of the Hall sensor to accurately measure movement may significantly affect the performance of machinery such as an engine. Ideally, the output signal of the Hall sensor should immediately begin to increase when a rising edge of a gear tooth approaches the Hall plate and should immediately decline as the gear tooth recedes from the sensor. Additionally, neither manufacturing tolerances nor physical stress on the sensor should affect its operation. In practice, however, timing delay from the Hall sensor circuitry, manufacturing tolerances, physical stress and other factors degrade the performance of the Hall sensor. As the performance of the Hall sensor is degraded, the performance of the machine in which it operates may also be degraded.
In order to avoid some of the practical problems associated with Hall sensors, the prior art has disclosed using a four terminal Hall device such as that shown in FIG.
1
. In
FIG. 1
, the Hall plate
11
incorporates four terminals (
2
,
4
,
6
and
8
) connected to two switch pairs
12
and
14
that alternately connect the Hall plate to a voltage source
13
ground
10
or output lines
15
,
15
′. The switch pairs operate in conjunction with each other so that, for example, when terminal
2
is connected to voltage source
13
, terminal
6
is connected to ground
10
terminal
8
is connected to output line
15
and terminal
4
is connected to output line
15
′. As a result, a voltage output is developed on output lines
15
,
15
′. Alternatively, when terminal
4
is connected to ground
10
, terminal
8
is connected to voltage source
13
then the voltage output lines are connected to terminals
2
and
6
.
The switch pairs
12
and
14
continually switch back and forth in response to a clock signal (not shown). In this way, the source of the output voltage continually switches from terminal pair
4
and
8
to terminal pair
2
and
6
. By switching the output voltages between the two terminal pairs, the effects of practical problems such as manufacturing tolerances and physical stress are minimized. This is because the measured output voltage signal (V
out
) is composed of two parts—V
(sig)
and V
(os)
. V
(sig)
is a function of the proximity of the gear tooth to the Hall plate and V
(os)
is an error component that is a function of various physical factors. When the measured output voltage signal from the two terminal pairs are combined, the error components largely cancel out. As a result, the effects from the practical problems of using Hall effect sensors are minimized.
The circuitry that processes the output voltage from the four terminal Hall device is shown in FIG.
2
. This circuitry in combination with the Hall device of
FIG. 1
creates a Hall sensor. In the circuitry of
FIG. 2
, the output terminals
15
,
15
′ from the Hall device are connected to operational amplifier (“op amp”)
40
. The output of op amp
40
is stored in capacitor
48
when a clock signal from the clock
42
has a high logic state. The output from Op Amp
40
is stored in capacitor
46
when clock
42
has a low logic state. The switch pairs
12
and
14
also operate in conjunction with the clock
42
. As a result, the output voltage measured between the terminal pair
4
and
8
is stored in capacitor
48
and the voltage measured at terminal pair
2
and
6
is stored in capacitor
46
. Both capacitors
48
and
46
have a common connection which, in effect, combines the two output voltage signals. Finally, op amp
47
then creates the final Hall sensor output signal.
While the Hall sensor shown in
FIGS. 1 and 2
does minimize some problems associated with general Hall sensors, it also creates problems of its own. In particular, the introduction of capacitors
46
and
48
to store the output voltage signal inherently introduces a timing delay in the system. That is, because of at least the capacitors
46
and
48
, the time at which the output signal from amplifier
47
changes in response to the passing of a gear tooth may be significantly delayed from the actual time the gear tooth passed the Hall plate. This delay in the system impairs the performance of the Hall sensor in various applications.
OBJECTS OF THE INVENTION
It is an object of the present invention to improve the performance of a Hall effect sensor.
It is another object of the present invention to improve the performance of a Hall effect sensor by improving the sensor's ability to compensate for thermal errors introduced into the sensor output voltage signal.
It is a further object of the present invention to improve the performance of a Hall effect sensor by improving the sensor's ability to compensate for physical stress related errors in the sensor output voltage signal.
It is still another object of the present invention to improve the performance of a Hall effect sensor by reducing the delay time in the sensor output voltage signal.
SUMMARY OF THE INVENTION
An improved Hall effect sensor includes a four-terminal Hall plate with orthogonally paired terminals that produce voltage signals in response to changes in an ambient magnetic field created by the proximity of a ferrous gear tooth to the sensor. Voltage signals from orthogonally paired terminals of the Hall plate are controlled by switches that are coupled to a clock signal generator. In response to the clock signal, the switches allow current to flow in a first direction corresponding to a first phase of the clock and to flow in a second direction corresponding to a second phase of the clock. A plurality of pass gate transistors in the sensor circuitry are connected to a timing generator synchronized with the clock signal generator. The timing generator outputs are received by the gate transistors and the gate transistors control the sequence in which a plurality of capacitors are charged. This plurality of capacitors store the voltage output from the Hall plate. The capacitors are
Biron Marc
De Winter Rudi
Hiligsmann Vincent
Harper Blaney
Jones Day Reavis & Pogue
Melexis N.V.
Oda Christine
Zaveri Subhash
LandOfFree
High speed densor circuit for stabilized hall effect sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High speed densor circuit for stabilized hall effect sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High speed densor circuit for stabilized hall effect sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2536086