JPS6258707A - Amplifier circuit for hall element - Google Patents

Abstract

PURPOSE:To compensate the output voltage of a Hall element by permitting the automatic adjustment of the gain of the first amplifier circuit by a bias circuit and to make stable a circuit against variance by supplying bias to the first and the second amplifier circuits by a common bias circuit. CONSTITUTION:A temperature compensation can be performed by giving an appropriate bias from a bias circuit 11 and making change the operating current I of the first differential amplifier circuit 9 in the opposite direction of the output voltage VH of a Hall element 8. When the output voltage of the first differential amplifier circuit 9 is temperature-compensated, no compensation in the second differential amplifier circuit 10 and the succeeding stage is required. By supplying a fixed bias by the common bias part 12 of the bias circuit 11 and the second bias part 14 regardless of a temperature change, the gain in the second differential amplifier 10 is maintained at a fixed level, and the output voltage is also kept at a fixed level. Therefore, by supplying the bias corresponding to the temperature change and an unchanged bias against a temperature from a single bias circuit 11, an amplifier circuit that is able to stably amplify the output voltage of the Hall element.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a Hall element amplification circuit for amplifying the output voltage of a Hall element, and particularly relates to a Hall element amplifier circuit for amplifying the output voltage of a Hall element. It is an object of the present invention to provide an amplifier circuit for a Hall element that can compensate for voltage.

(b) Conventional technology A Hall element is a magnetoelectric conversion element that converts magnetic field strength into an electric signal based on the Hall effect, and is currently widely used as a 5-position sensor or a rotation sensor.

Therefore, the output voltage ■4 of the Hall element is y, , = −
It can be expressed as (1), but since its level is very small,
Signal processing cannot be performed directly.

Furthermore, in the above equation (1), the Hall constant R, which indicates the characteristics of the Hall element, is:

R, = ρ・μ ・・・・・・・・・(2
) [where ρ is specific resistance and μ is mobility], and the temperature characteristics of the Hall constant R are as follows.

−φ”ltop−1=ρ”1/−−F μgo1g−...
...... (3) dT dT dT It is expressed as. Therefore, the output voltage of the Hall element has a temperature change that depends on the temperature characteristics of the specific resistance ρ and mobility μ, and the relative sensitivity change with respect to temperature during constant voltage driving is 0 for the silicon Hall element at °C. It becomes about .6%/°C, which cannot be ignored in practical terms.

What is the relative sensitivity change with respect to temperature of the Hall element?

Compensation can be performed in an amplifier circuit that amplifies the output voltage of the Hall element. National Technical Report published December 1975
Vol, 21 Den 6, pages 681 to 691, [
A paper entitled "Magnetic Sensing Element/Monolithic Hall ICj" is described in the paper, page 685, FIG. 7, which describes a circuit for amplifying the output '1 anal pressure of a Hall element having a degree compensation circuit. The circuit includes a first differential amplifier circuit (1) that differentially amplifies the output voltage of the Hall element (1) as shown in FIG.
and a second differential amplifier circuit (sword) that further amplifies the output signal of the first differential amplifier circuit (2),
A temperature compensation diode (6) is connected to the common emitter of the pair of transistors (4) and (5) constituting the first differential amplifier circuit. Therefore, since the pair of transistors (4) and (5) forming the first differential amplifier circuit are connected to the output terminal of the Hall element (1), the voltage thereof becomes 'vcc'. The operating current of the first differential amplifier circuit (2) is .

■. =(--(v□+vo)・π...(4). In the above equation (4), ■□ and V have negative usage characteristics, so when the temperature rises, the above operation The current 1° is increased. Also, since R has a positive temperature characteristic, the operating current is reduced. Therefore, the Hall element (1°) is increased.
) with a diode (6) for attitude compensation at the rear stage.
By connecting a differential amplifier circuit (RI), when the output voltage V□ of the Hall element (1) decreases due to an increase in temperature, the first
Since the operating current of the differential amplifier circuit (2) can be increased and the gain of the first differential amplifier circuit (2) can be increased, the output voltage of the first differential amplifier circuit (2) can be approximately reduced. It can be kept constant.

(c) Problems that the invention seeks to solveHowever,
In the case of the conventional circuit shown in Figure 2, temperature compensation is performed using a diode (6).
Since the operating current of the first differential amplifier circuit (2) cannot be changed sufficiently in response to temperature changes, it is not possible to sufficiently compensate for the decrease in the output voltage of the Hall element (1). Therefore, there was a problem that the output voltage of the first differential amplifier circuit (21) fluctuated.
If multiple diodes are connected in series instead of using individual diodes, it is possible to perform more precise compensation, but there are problems such as less freedom in design since only discrete compensation can be performed, and reduced voltage characteristics. This is not a preferred method because it causes the problem of deterioration.

Furthermore, in the case of the conventional circuit shown in FIG. 2, the first differential amplifier circuit (
Since the operating current of the second differential amplifier circuit (winter) and the operating current of the second differential amplifier circuit (S) are set independently from each other, there is a risk that the operating point may change due to variations in the elements, making it impossible to connect with the subsequent stage. was there.

B) Means for Solving the Problems The present invention has been made in view of the above points, and provides a bias that increases the gain of the first amplifier circuit that amplifies the output voltage of the Hall element with respect to positive temperature changes. The present invention is characterized in that it is provided with a bias circuit that supplies a bias to maintain a substantially constant operating current of a second amplifier circuit that amplifies the output of the first amplifier circuit.

(E) Function According to the present invention, the gain of the first amplifier circuit can be automatically adjusted by the bias circuit, so that the output voltage of the Hall element can be compensated. Further, since bias is supplied to the first and second amplifier circuits by a common bias circuit, it is possible to provide an amplifier circuit for a Hall element that is stable against variations and is particularly suitable for IC implementation.

(f) Embodiment Figure 1 is a circuit block diagram showing the principle of the present invention.
) is a Hall element, (9) is a first differential amplifier circuit that amplifies the output voltage of the Hall element (8), and 00 is a second differential amplifier that amplifies the output voltage of the first differential amplifier circuit (9). an amplifier circuit, and (b) a common bias section (2), a first bias section σ3 that provides an operating current for the first differential amplifier circuit (9), and a first bias section σ3 that provides an operating current for the second differential amplifier circuit () (Th). This is a bias circuit consisting of a second bias section α→ which gives .

Now, at a predetermined temperature T, the output voltage of the Hall element (8)
If it is assumed that {circle around (2)}, then the output voltages v and l decrease to VII2 when the temperature rises to T2. on the other hand.

The common bias section (6) and the first bias section (2) of the bias circuit (b) are connected to the first differential amplifier so that the gain G of the first differential amplifier circuit (9) becomes G at the temperature T. If the bias supplied to the circuit (9) is set, the output voltage VI of the first differential amplifier circuit (9) at @degree T, becomes ■, 2G, .
It will become 7M1. The first differential amplifier circuit (9
) in order for the output voltage V2 to become V, = V, the gain G of the first differential amplifier circuit (9) at the temperature T.

The common bias section (6) sets the operating current to such a value.
By creating the first bias section, the output voltage of the first differential amplifier circuit (9) can be kept constant despite temperature changes. Generally, the gain G of a differential amplifier circuit is 9m-9 depending on its mutual conductance gm and load resistance RL.
Set in RL. And the mutual conductance 1
Since m is proportional to the operating current 1°, after all, an appropriate bias is applied from the bias circuit αD, and the first
Operating current I of the differential amplifier circuit (9). Hall element (8)
Temperature compensation can be achieved by changing the output voltage ■1 in the opposite direction to the temperature change.

Further, if the output voltage of the first differential amplifier circuit (9) is temperature-compensated, there is no need for compensation in the second differential amplifier circuit αO and the subsequent stage, and the second differential amplifier circuit The QO must have a constant gain.As mentioned above, the gain of the second differential amplifier circuit αO is also determined by the mutual conductance and the load resistance.
Since the mutual conductance is determined according to the operating current, the common bias section (6) and the second bias section (14) of the bias circuit are designed to supply a constant bias even if there is a temperature change. For example, the gain of the second differential amplifier circuit (old) is kept constant and the output voltage is also constant. Therefore, as shown in FIG.
By supplying a bias that corresponds to the temperature change and a bias that does not change with respect to temperature from (b), an amplifier circuit that can stably amplify the output voltage of the Hall element can be obtained.

FIG. 3 shows a specific example of a circuit according to the present invention.

The output voltage of the Hall element (8) is determined by the first differential amplifier circuit (Dan).
The signal is applied to the bases of the first and second transistors constituting (to) and αG, and is amplified. The output signal of the first differential amplifier circuit (the output signal of the first differential amplifier circuit) is
After the voltage is applied from the collectors of and (g) to the bases of the third and fourth transistors α and (to) constituting the second differential amplifier circuit (9) and is further amplified, the voltage is applied to the fifth and sixth transistors 09 and The bias circuit is a common bias section consisting of first and second resistors Q1) and (2) and diode-connected first and second bias transistors Q1 and (C). , a third bias transistor (1) whose base is connected to the second bias transistor (C), a fourth bias transistor (1) serving as an operating current source of the first differential amplifier circuit (Z), and the fourth bias transistor (C). a first bias section consisting of a third resistor wire connected to the emitter of the second bias transistor (c), and a second bias section connected to the second bias transistor (c) as a current mirror and serving as an operating current source for the second differential amplifier circuit. The second bias section (b) includes a fifth bias transistor @ and a fourth resistor wire connected to the emitter of the fifth bias transistor wire.

Therefore, the current (1) flowing through the common bias section (2) is the collector current of the fourth bias transistor (a), that is, the operating current of the first differential amplifier circuit (9). 1
teeth.

1o+ ” R, (IIR2+ V++t Vats
−v+v< )−(6). By the way, the temperature coefficient of V□ of a transistor changes depending on the current flowing through its PN junction, and the lower the optical density, the more the temperature coefficient becomes smaller.

The operating current (2) of the first differential amplifier circuit (D) shown by the above equation (6). Among the requirements for determining 1, since the third bias transistor value only supplies the base current of the fourth bias transistor (e), the seismic intensity coefficient of the pace-emitter voltage ■□3 becomes large. Therefore, as the temperature rises, the above ■□ becomes smaller.

The operating current IQ+ increases, the gain of the first differential amplifier circuit (Dan) increases, and the Hall element (8) due to temperature rise increases.
) to compensate for the decrease in the output voltage v, I. In that case.

Compared to the current flowing through the third bias transistor (A), the current flowing through the first bias transistor (A) is higher than the current flowing through the third bias transistor (A). Since the currents flowing through the second and fourth transistors (c), (c), and (a) are sufficiently large, the operating current is as follows. , does not contribute much to changes in .

The second bias transistor (c) constituting the common bias section
A current mirror connection is made to the fifth transistor @ of the bias section (b). The operating current of the second differential amplifier circuit is I
. , then ■. 2 ” R, (II R2+V,.-1,)...
...(7). Therefore, if the value of the second resistor (a) and the value of the fourth resistor wire are set equal, the current flowing through the second bias transistor (c) and the current flowing through the fifth bias transistor wire will be equal. ■、A"Vl
15, and the operating current and gain of the second differential amplifier circuit become stable against temperature changes.

Therefore, by configuring as shown in Figure 3, it is possible to supply an operating current with temperature characteristics to the first differential amplifier circuit from a single bias circuit, and to supply the second differential amplifier circuit with an operating current that is stable against temperature changes. Can supply operating current.

In addition, if the amount of compensation is small in FIG. 3, the third bias transistor (A) may have a Darlington configuration,
When compensating for temperature changes in the power supply voltage, the third bias transistor (A) and the fourth bias transistor (E) are connected between the first resistor (C) and the first bias transistor (H).
Transistors may be inserted between the second bias transistor (c) and the fifth bias transistor (c).

(g) Effects of the Invention As described above, the present invention provides an amplifier for a Hall element that can compensate for temperature changes in the output voltage of the Hall element and can facilitate connection with subsequent stages. We can provide the circuit. Further, according to the present invention, since the operating current of the first and second amplifier circuits is supplied from a common bias circuit, it is possible to provide an amplifier circuit for a Hall element with a simple configuration and less variation. It is suitable for use in IC.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing the principle of the present invention. FIG. 2 is a circuit diagram showing a conventional Hall element amplifier circuit, and FIG. 3 is a circuit diagram showing a specific circuit example of the present invention. Explanation of main drawing numbers (8)...Hall element, (9)...First differential amplifier circuit, ao...Second differential amplifier circuit, ■...Bias circuit. (A)...Common bias section, α3...First bias section. αXun...Second bias section.

Claims (1)

[Claims] (1) A Hall element amplifier circuit for amplifying the output voltage of the Hall element, comprising a first amplifier circuit that amplifies the output voltage of the Hall element, and a second amplifier circuit that amplifies the output voltage of the first amplifier circuit. an amplifier circuit, and a bias that increases the gain of the first amplifier circuit in response to a positive temperature change is supplied to the first amplifier circuit, and a bias that makes the operating current of the second amplifier circuit substantially constant. An amplifier circuit for a Hall element, comprising a bias circuit that supplies the second amplifier circuit.