JPH08320266A - Constant current driving circuit, and integrated semiconductor sensor using it - Google Patents

Abstract

PURPOSE: To provide an integrated semiconductor sensor in which a constant current driving circuit having a constant current characteristic of zero temperature coefficient is integrated with a piezoresistance element to allow a downsizing and an excellent sensitivity temperature compensation. CONSTITUTION: A bridge circuit 21 using a piezoresistance, and a constant current driving circuit 13 for driving it are integrated into a sensor chip. The first transistor Q1 of the constant current driving circuit 13 is connected to Vcc through the bridge circuit 21, the emitter is earthed through a resistor R1, and the base is connected to Vcc through a resistor R2. The collector. and base of the second transistor Q2 are connected to the base and emitter of the first transistor Q1, respectively, and the emitter is earthed through a resistor R3. The collector and base of the third transistor Q3 are connected to the collector and emitter of the first transistor Q1, respectively, and the emitter is earthed through a fourth resistor R4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current drive circuit for supplying a constant drive current to a load circuit regardless of its resistance change, and an integrated semiconductor sensor using the constant current drive circuit.

[0002]

2. Description of the Related Art A semiconductor pressure sensor is obtained by forming a piezoresistive element in an array on a single crystal silicon substrate in the same manner as in the IC manufacturing, and scraping the back surface to produce a pressure sensitive diaphragm portion. A semiconductor pressure sensor is usually used with an electronic circuit that performs offset adjustment, temperature compensation, output amplification, and the like. Recently, in order to miniaturize the semiconductor pressure sensor, an integrated semiconductor sensor in which a thin film resistor and other peripheral circuits are integrally integrated on a sensor chip is also manufactured. The integrated semiconductor pressure sensor is used, for example, for measuring the intake pressure of an automobile engine, measuring the suction pressure of a household vacuum cleaner, and the like.

In a semiconductor pressure sensor, in particular, the rate of change in resistance value due to the piezoresistive effect greatly depends on temperature, and temperature compensation of sensitivity is important. Usually, in order to perform temperature compensation of this sensitivity, a constant current drive circuit is used which optimizes the surface concentration of the piezoresistive element and drives a load circuit composed of the piezoresistive element with a constant current regardless of the resistance change.
As such a constant current drive circuit, one using an operational amplifier OP and a resistor R as shown in FIG. 4 is generally known.

[0004]

However, the conventional constant current drive circuit, for example, in the case of using an operational amplifier, usually requires a capacitor or the like to prevent oscillation. Therefore, when it is incorporated in an integrated semiconductor sensor, the chip area is reduced. Has the drawback of becoming larger. In addition, a constant current drive circuit that does not use an operational amplifier is used in the base-emitter voltage V of the transistor.
It is difficult to obtain a precise constant current because the current has a temperature coefficient due to the temperature dependence of BE.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a constant current drive circuit which can easily obtain a constant current characteristic of zero temperature coefficient without using an operational amplifier. To aim. Another object of the present invention is to provide an integrated semiconductor sensor in which the above-described constant current drive circuit is integrated with a piezoresistive element, which enables miniaturization and excellent sensitivity temperature compensation.

[0006]

The present invention is, firstly, a constant current drive circuit for supplying a constant drive current to a load circuit irrespective of its resistance change, and a collector having a power supply terminal via the load circuit. A first bipolar transistor having an emitter connected to a reference potential end via a first resistor and a base connected to the power supply terminal via a second resistor, and a collector and a base respectively connected to the first bipolar transistor. A second bipolar transistor which is connected to the base and emitter of the first bipolar transistor, and whose emitter is connected to the reference potential terminal through a third resistor.
And a third bipolar transistor having a collector and a base connected to the collector and the emitter of the first bipolar transistor, respectively, and an emitter connected to the reference potential terminal through a fourth resistor. Is characterized by.

Secondly, the present invention is, on a semiconductor substrate on which piezoresistive elements are arranged and formed, a constant current drive for supplying a constant drive current to a load circuit composed of the piezoresistive elements irrespective of the resistance change. In the integrated semiconductor sensor having integrated circuits, the constant current drive circuit has a collector connected to a power supply terminal via a load circuit and an emitter connected to a first side.
A first bipolar transistor whose base is connected to the power supply terminal via a second resistor and whose collector and base are respectively connected to the reference potential terminal via the resistor and the base and emitter of the first bipolar transistor. A second bipolar transistor having an emitter connected to the reference potential terminal via a third resistor, a collector and a base connected to the collector and the emitter of the first bipolar transistor, respectively, and an emitter And a third bipolar transistor connected to the reference potential end via the resistor 4.

[0008]

The constant current drive circuit according to the present invention has the first to fourth aspects.
By selecting the resistance value of the resistor, the base-emitter voltage V of the bipolar transistor in the output current formula
The BE coefficient can be zero, and the output current supplied to the load circuit can be constant regardless of temperature. That is, without using an operational amplifier, with a simple circuit configuration,
The temperature coefficient of the output current can be zero.

Further, if the above-mentioned constant current drive circuit is incorporated into an integrated semiconductor sensor, the constant current drive circuit is simple and a capacitor as in the case of using an operational amplifier is not required. Can be miniaturized. If thin-film resistors are used as the first to fourth resistors and their resistance values are adjusted by laser trimming or the like,
Even if there is a variation in the resistance value, it is possible to reliably obtain a constant current characteristic with a temperature coefficient of zero.

In particular, when the resistance values of the first, second, third and fourth resistors are R1, R2, R3 and R4 respectively, they are set to satisfy the condition of R2 = 2R1 + R3 R3 = R4. As a result, the temperature coefficient of the output current becomes zero.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1A and 1B are a plan view showing a chip structure of an integrated semiconductor pressure sensor according to an embodiment of the present invention and a sectional view taken along the line AA '. According to a normal process, the thin diaphragm portion 11 of the single crystal silicon substrate 10 is diffused with impurities to cause piezoresistive elements ra, rb, rc, rd.
Are arrayed. Here, the resistance elements ra and rd exhibit resistance changes in the same direction with respect to pressure, and the resistance elements rb and r
c changes resistance in the opposite direction to the resistance elements ra and rd. A constant current drive circuit 13 and other peripheral circuits (not shown) are formed in the peripheral thick portion 12.

Although wiring and the like are omitted in FIG. 1, in this embodiment, for example, as shown in FIG.
A full-bridge type bridge circuit 21 using a, rb, rc, and rd is configured. The constant current drive circuit 13 supplies a constant output current Iou to the bridge circuit 21 as a load circuit.
It supplies t.

FIG. 3 shows a specific configuration of the constant current drive circuit 13. First to third bipolar transistors Q1
-Q3 are all npn transistors. The first to fourth resistors R1 to R4 are thin film resistors such as metal thin films or polycrystalline silicon thin films. The first transistor Q1 has a collector connected to a power supply terminal Vcc via a bridge circuit 21 which is a load circuit, an emitter connected to a ground terminal which is a reference potential end via a first resistor R1, and a base connected to a first terminal. It is connected to VCC through a resistor R2.

The collector and base of the second transistor Q2 are connected to the base and emitter of the first transistor Q1, respectively, and the emitter is grounded via a third resistor R3. The third transistor Q3 has a collector,
The bases are connected to the collector and the emitter of the first transistor Q1, respectively, and the emitter is grounded via the fourth resistor R4.

It will be specifically described that the constant current drive circuit 13 thus configured provides a constant current Iout to the bridge circuit 21 which is a load circuit. FIG.
, The first, second and third transistors Q1,
The collector currents of Q2 and Q3 are IC1, IC2 and I, respectively.
C3. The resistance values of the first to fourth resistors R1 to R4 will be described as R1 to R4.

As a precondition, first, a second transistor Q2 and a third transistor Q3 whose bases are commonly connected are used.
The third resistor R3 and the fourth resistor R4 provided in the respective emitters are set in advance in the relationship of the following mathematical expression 1.

[0017]

[Equation 1] R3 = R4

Therefore, the collector current I C2 of the second transistor Q2 and the collector current I of the third transistor Q3 are
It is equal to C3 and satisfies the relationship of the following formula 2.

[0019]

[Equation 2] IC2 = IC3

Under the above assumptions, all the transistors Q
With the base-emitter voltage of 1 to Q3 as VBE, first, the following formula 3 is obtained by focusing on the path from the second resistor R2 to the base → emitter → first resistor R1 of the first transistor Q1.

[0021]

[Equation 3] R2 IC2 + VBE + R1 IC1 = VCC

Further, focusing on the path from the second resistor R2 to the collector → emitter → third resistor R3 of the second transistor Q2, the following equation 4 is obtained.

[0023]

[Equation 4] R2 IC2 + 2VBE + R3 IC2 = VCC

Output current Iout applied to the bridge circuit 21
Is the sum of the collector currents of the first and third transistors Q1 and Q3, and is given by the following equation 5.

[0025]

[Equation 5] Iout = IC1 + IC3

From Equations 3 and 4, I C1 and I C2 are calculated, and
Substituting this into Equation 5 in consideration of the output current Iout
Is calculated from the relationship between VCC and VBE as shown in the following expression 6.

[0027]

(Equation 6)

From the result of the above equation 6, the output current Iout depends on the base-emitter voltage VBE of the transistor by setting the first to third resistors R1 to R3 so as to satisfy the following equation 7. Not a constant value.

[0029]

[Equation 7] R2 = 2R1 + R3

That is, by setting the relation of the resistance values so as to satisfy the relation of the equation 7, the constant current drive circuit 13 of this embodiment is affected by the base-emitter voltage VBE of the transistor having temperature dependency. Output current Iout having a temperature coefficient of zero can be supplied to the load.

When the relationship of the equation 7 is not completely satisfied due to, for example, manufacturing variations, the temperature dependence of VBE is exhibited. In such a case, one of the resistors R1, R2 and R3 is adjusted by laser trimming. Which is to be adjusted can be determined by measuring whether the temperature coefficient of the output current Iout is positive or negative, as is apparent from the equation (6).

As described above, according to this embodiment, there is no need to use an operational amplifier, therefore, no capacitor is required, and a constant current drive circuit capable of obtaining a constant current with a temperature coefficient of zero is integrated in a small size. The semiconductor pressure sensor can be obtained. An integrated pressure sensor equipped with a conventional constant current circuit that actually uses an operational amplifier has a chip area of 3 mm.
While it is about 3 mm, it is 2.6 in this embodiment.
It was possible to reduce the size to mm x 2.6 mm. Further, since the chips are smaller, more chips can be manufactured at the same time, which improves productivity by about 25%.

Although the integrated pressure sensor has been described in the embodiment, the present invention can be similarly applied to an acceleration sensor constituted by using the same piezoresistive element. Particularly, in the case of a three-dimensional acceleration sensor, three sensor driving circuits are required, so that the effect of chip miniaturization when integrated is large. The constant current drive circuit described in the embodiment is not limited to the integrated semiconductor sensor,
More generally, it can be applied to various applications that require a precise constant current with a temperature coefficient of zero.

[0034]

As described above, according to the present invention, by selecting the resistance value, a simple constant current drive circuit that can make the output current supplied to the load circuit constant regardless of the temperature is provided. can get. In particular, if the constant current drive circuit of the present invention is incorporated in a semiconductor sensor chip, an integrated semiconductor sensor having an excellent sensitivity temperature compensation function and a chip size reduction can be obtained.

[Brief description of drawings]

FIG. 1 shows a chip structure of an integrated semiconductor sensor according to an embodiment of the present invention.

FIG. 2 shows an equivalent circuit of the semiconductor sensor of the embodiment.

FIG. 3 shows a specific configuration of a constant current drive circuit of the same embodiment.

FIG. 4 shows a configuration of a constant current drive circuit in a conventional semiconductor pressure sensor.

[Explanation of symbols]

10 ... Single crystal silicon substrate, 11 ... Thin diaphragm part, 12 ... Peripheral thick part, 13 ... Constant current drive circuit, ra,
rb, rc, rd ... Piezoresistive element, 21 ... Bridge circuit (load circuit), Q1 ... First transistor, Q2 ... Second transistor, Q3 ... Third transistor, R1 ...
1st resistance, R2 ... 2nd resistance, R3 ... 3rd resistance, R
4 ... Fourth resistance.

Claims (2)

[Claims] 1. A constant current drive circuit for supplying a constant drive current to a load circuit regardless of its resistance change, wherein a collector is connected to a power supply terminal via the load circuit and an emitter is connected via a first resistor. Is connected to the reference potential terminal and the base is connected to the power supply terminal through a second resistor.
A second bipolar transistor having a collector and a base connected to the base and the emitter of the first bipolar transistor, respectively, and an emitter connected to the reference potential terminal through a third resistor; Constant current drive characterized in that the base has a third bipolar transistor connected to the collector and the emitter of the first bipolar transistor, respectively, and the emitter connected to the reference potential terminal through a fourth resistor. circuit. 2. A constant current drive circuit for supplying a constant drive current to a load circuit made up of the piezoresistive elements, regardless of the resistance change, is formed on a semiconductor substrate on which the piezoresistive elements are arrayed. In integrated semiconductor sensors,
In the constant current drive circuit, a collector is connected to a power supply terminal via a load circuit, an emitter is connected to a reference potential end via a first resistance, and a base is connected to the power supply terminal via a second resistance. First done
A second bipolar transistor having a collector and a base connected to the base and the emitter of the first bipolar transistor, respectively, and an emitter connected to the reference potential terminal through a third resistor; An integrated semiconductor, the base of which is connected to the collector and the emitter of the first bipolar transistor, and the third bipolar transistor of which the emitter is connected to the reference potential terminal through a fourth resistor. Sensor.