JPH0413982A - Sensor drive circuit - Google Patents

Abstract

PURPOSE:To improve rising characteristic of a sensor by proving a feedback circuit with which an output signal from a differential amplification circuit is inputted into a current source to increase an amount of current to be supplied to a sensor section until an output signal from the feedback circuit reaches a specified reference value. CONSTITUTION:When receiving a magnetic field H from outside with a proper bias current applied to input terminals IN1 and IN2 by a current source 3, a magnetic sensor 2 feeds an output current to a differential amplifier 4 from output terminals OUT1 and OUT2 according to an intensity of the external magnetic field H and information on the intensity of the magnetic field H is outputted from the differential amplifier 4 based on the output current. As possibility is considered that an output voltage outputted from the differential amplifier 4 may be a negative value, it is converted into a positive value with an absolute value circuit 8 and the value is amplified with an amplifier 9 to be added to a reference voltage Vref of a power source E thereby causing an increase in an amount of current to be supplied to the magnetic sensor 2 from the current source 3.

Description

[Detailed Description of the Invention] C Overview] Regarding the sensor drive circuit, the present invention aims to provide a sensor drive circuit that improves the rise characteristics of the sensor, and provides a current source that supplies a predetermined current to a sensor section forming a bridge configuration. and a differential amplifier circuit that detects and amplifies the output of the sensor section, a feedback circuit that inputs an output signal from the differential amplifier circuit to the current source, and a feedback circuit that inputs an output signal from the differential amplifier circuit to the current source, The source is configured to increase the amount of current supplied to the sensor unit until the output signal from the feedback circuit reaches a predetermined reference value.

[Industrial application field]

The present invention relates to a sensor drive circuit, and more particularly to a sensor drive circuit that performs intermittent operation and is suitable for use in a bridge-configured sensor having temperature characteristics.

In recent years, so-called bridge circuits have been developed in which, for example, four impedances are connected in a diamond shape, and opposing corners are bridged with a power supply branch and a detector branch.When the bridge is in a balanced state, current flows to the detector branch. It is widely used in sensors by taking advantage of this property that there is no bridge structure, and as a result, many sensor drive circuits have been developed to drive sensors with this bridge configuration.

In such a sensor drive circuit, depending on the use of the sensor, for example, in the case of a portable sensor or a vehicle-mounted sensor, current supply may only be obtained from the battery. If a constant current is constantly supplied to the sensor drive circuit from a battery with a relatively small capacity, the operating time will be extremely short and it will not be practical. Therefore, in order to obtain a sufficient operating time, the sensor drive circuit must be operated intermittently. Moreover, even though the device operates intermittently, a stable output similar to that obtained when a constant current is constantly supplied is required.

[Prior art] As a conventional sensor drive circuit of this type, for example,
There is something like the one shown in the figure.

In FIG. 4, the sensor drive circuit 1 has a bridge configuration and a ferromagnetic magnetoresistive element (hereinafter referred to as MR) as a sensor section.
A magnetic sensor 2 using a magnetic sensor (referred to as an element), a current a3 that supplies a predetermined bias current to the magnetic sensor 2, and a differential amplifier 4 as a differential amplifier circuit that detects and amplifies the output from the magnetic sensor 2. . Note that S is a switch that activates or deactivates the current source 3 at predetermined time intervals by a control means (not shown).

As shown in FIG. 4, when the magnetic sensor 2 receives an external magnetic field H with an appropriate bias current applied to the input terminals INI and IN2 by the current source 3, it outputs an output according to the strength of the external magnetic field H. An output current is passed through the differential amplifier 4 from the terminals 0UTI and 0UT2, and information on the strength of the magnetic field H is output from the differential amplifier 4 based on this output current. In addition, the current source 3 is activated or stopped at predetermined intervals by the switch S, that is, the sensor drive circuit 1 is operated intermittently, so that it appears that a constant current is constantly supplied to the magnetic sensor 2. While the same operation is performed, current consumption is suppressed.

[Problem to be solved by the invention]

However, in such a conventional sensor drive circuit, since the sensor part uses a bridge-configured magnetic sensor 2 having temperature characteristics, as shown in FIG. The formula that expresses the rise characteristics of offset output 1 to output when the power is turned on is, where Voff is the offset output voltage, voff・(1-e-1'7)...
- (τ is a temperature characteristic), which is represented by the second symbol, and has a characteristic that gradually rises until the magnetic sensor 2 reaches a thermal equilibrium state. Therefore, even if intermittent operation is performed to reduce current consumption, the magnetic sensor 2 may be switched from the on state to the off state without stabilizing the sensor output and health, as shown in FIG. This makes it difficult for the differential amplifier 4 to determine the output level of the magnetic sensor 2. Therefore, it is conceivable to turn on the current source 3 until the output level of the magnetic sensor 2 becomes stable, but then the current source 3 will remain on for a long time, reducing power consumption due to intermittent operation. There was a problem in that the effect of oxidation became less effective.

Therefore, in order to increase the effect of reducing power consumption through intermittent operation, the present invention aims to improve the rise characteristics of the sensor.
The present invention aims to provide a sensor drive circuit that achieves the following two objectives.

[Means to solve the problem]

In order to achieve the above object, the sensor drive circuit according to the present invention, as shown in the principle diagram in FIG. In the sensor drive circuit 1 comprising a differential amplification circuit 4 that detects and amplifies, the differential amplification circuit 4
A feedback circuit 5 is provided to manually input an output signal from the feedback circuit 5 to the current source 3, and the current source 3 increases the amount of current supplied to the sensor section 2 until the output signal from the feedback circuit 5 reaches a predetermined reference value. It is configured to do so.

[Effect]

In the present invention, the amount of current supplied to the sensor unit is increased until the output signal output from the feedback circuit to the current source reaches a predetermined reference value.

Therefore, as the amount of current supplied to the sensor section increases, the rise characteristics of the offset output in the sensor section are improved.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

Figures 2 and 3 are diagrams showing one embodiment of the sensor drive circuit according to the present invention, and in these Figures 2.3, the same numbers as in the conventional example shown in Figure 4.5 indicate the same or equivalent parts. .

First, the configuration will be explained.

Fig. 2 is a schematic circuit diagram showing the overall configuration of this embodiment.
, a current source 3, a differential amplifier 4, and a feedback circuit 5. The sensor of the sensor drive circuit 1 in this embodiment is, for example, a magnetic sensor that detects the strength of an external magnetic field H using an MR element. 2 is used.

The current source 3 is composed of a bipolar transistor Q1, a capacitor C1, resistors R1 and R2, an operational amplifier 6, and voltages 'a' and E. A low-pass filter 7 is composed of the capacitor C1 and the resistor R1.

The feedback circuit 5 includes an absolute value circuit 8 that takes the absolute value of the output from the differential amplifier 4 having a gain AI, an amplifier 9 having a gain A2, a capacitor C2 and a resistor R2 forming a differentiating circuit. Note that Rs is a resistance.

Next, the effect will be explained.

First, as in the conventional example, when the magnetic sensor 2 receives an external magnetic field H with an appropriate bias current applied to the input terminals INI and IN2 by the current source 3, the magnetic sensor 2 receives an external magnetic field H.
An output current is caused to flow from the output terminals 0UTI and 0UT2 to the differential amplifier 4 according to the strength of the magnetic field H, and information on the strength of the magnetic field H is output from the differential amplifier 4 based on this output current. Since the output voltage output from the differential amplifier 4 may be a negative value, it is converted to a positive value by the absolute value circuit 8, and this value is amplified by the amplifier 9 and sent to the capacitor C2.
It is added to the reference voltage Vref of the power source E via a differentiating circuit consisting of a resistor R2 and a resistor R2, and the amount of current supplied from the current source 3 to the magnetic sensor 2 is increased. That is, in Figure 3,
As shown by the large solid line, the formula representing the rise characteristics of the offset output in this embodiment is the formula representing the rise characteristics of the offset output in the conventional example, Voff(1-e-"?
) is multiplied by Az (Voff/Vref), and as shown by the - dotted chain line in the figure, Voff ・(1+
It is expressed by the formula A2・Voff/Vref)・(1-e ``').For reference, compared to the conventional example shown by the solid line in the same figure, the time required to reach the predetermined offset voltage Voff is However, if the current applied to the magnetic sensor 2 continues to increase, the offset output voltage will rise more than necessary, so in this embodiment, the output is reduced by a differentiating circuit consisting of a capacitor C2 and a resistor R2. When the predetermined offset voltage Voff is reached, the amount of current flowing through the magnetic sensor 2 is reduced, and the time constant e −t/CR of this differentiator circuit is used as shown by the broken line in the figure.
Increase in offset output voltage can be suppressed. In order to prevent divergence due to the differentiating circuit provided to suppress the offset output voltage from increasing more than necessary,
Delay compensation is performed by a low-pass filter.

As described above, in this embodiment, as the amount of current supplied to the sensor section increases, the rise time of the offset output in the sensor section is shortened, and the rise characteristics of the offset output are improved.

Therefore, since the time required for the output level of the magnetic sensor 2 to reach a stable state is short, sufficient power consumption can be reduced when the sensor drive circuit 1 is operated intermittently.

Note that, although the above embodiment has been described by taking as an example a sensor drive circuit that drives a magnetic sensor using an MR element, the present invention is not limited to this, and the sensor may be any sensor having a bridge configuration that has temperature characteristics.

FIG. 6 is a waveform diagram showing the rise characteristics of the off-cent output voltage during intermittent operation of the conventional example.

(Effects of the Invention) In the present invention, by increasing the amount of current supplied to the sensor section up to a predetermined output level, the rise time of the offset output in the sensor section can be shortened, and the rise characteristics of the sensor can be improved. .

-...Sensor drive circuit, ...Magnetic sensor (sensor part), ...Variable current source (current source), ...Differential amplifier (differential amplifier circuit) )・・・・・・
feedback circuit.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIGS. 2 and 3 are diagrams showing an embodiment of the sensor drive circuit according to the present invention, FIG. 2 is a schematic circuit diagram showing the overall configuration, and FIG. A waveform diagram showing the rise characteristics of the offset output voltage when the power is turned on; Figure 4 is a schematic circuit diagram showing the overall configuration of the sensor drive circuit of the conventional example; Figure 5 is the offset output voltage of the conventional example when the power is turned on. Waveform diagram showing the rise characteristics of , Figure Time (1)

Claims (3)

[Claims] (1) A sensor comprising a current source (3) that supplies a predetermined current to a sensor section (2) forming a bridge configuration, and a differential amplifier circuit that detects and amplifies the output of the sensor section (2). The drive circuit (4) includes a feedback circuit (5) that inputs the output signal from the differential amplifier circuit to the current source, and the current source (3) receives the output signal from the feedback circuit (4) at a predetermined level. A sensor drive circuit characterized in that the amount of current supplied to the sensor section (2) is increased until a reference value of . (2) The sensor drive circuit according to claim 1, wherein the current source repeats activation and deactivation at predetermined time intervals. (3) The sensor drive circuit according to claim 1 or 2, wherein the sensor comprises a magnetoresistive element.