JPH05281254A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To facilitate compensation of offset voltage temperature characteristics of the entire sensor with a simple configuration by providing a differential operational amplifier circuit with a compensating circuit for adjusting the offset voltage at a chip stage. CONSTITUTION:A differential operational amplifier circuit consists of a bias circuit 31, a differential circuit 32 and an output buffer 33. A resistor R13 of a compensating circuit 34 is a thin film resistor farmed on an integrated circuit chip, and its resistance value is adjusted by laser trimming. By allowing a part of the current on an input transistor Q1 side to bypass by using a circuit 34, the collector current of two input transistors Q1 and Q2 can be set to different values, respectively. Therefore, by adjusting a resistor R13 through trimming, an input offset voltage is given. Since the temperature characteristics of the input offset voltage varies according to the magnitude of offset, the temperature drift of the offset as the entire sensor circuit can be compensated by giving an appropriate offset voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor using a strain sensitive gauge resistor, and more particularly to an integrated acceleration sensor in which an output amplifier circuit is integrally integrated with a strain sensitive gauge resistor bridge on a semiconductor substrate.

[0002]

2. Description of the Related Art A semiconductor acceleration sensor is known in which a strain sensitive gauge resistor is formed on a silicon cantilever or a diaphragm and is assembled into a bridge. In this type of semiconductor acceleration sensor, if high accuracy is required in a wide temperature range, sensitivity and temperature compensation of the zero point are required.
Although there are various specific temperature compensation methods, there is a method of attaching a resistor externally.

FIG. 5 shows an example of the circuit configuration of a strain-sensitive resistor bridge whose temperature is compensated by an external resistor. Ra,
Rb, Rc, and Rd are strain sensitive gauge resistors formed on a single silicon substrate, and these are combined to form a bridge. An external resistor Rp is connected in parallel with one strain sensitive gauge resistor Ra, and an external resistor RL is provided so as to short-circuit the bridge input. The resistor Rp is connected in parallel to the strain sensitive gauge resistor Rb on the opposite side according to the temperature characteristics. One external resistor Rp is for temperature compensation of the zero point (offset voltage) of the bridge, and the other external resistor RL is for temperature compensation of sensitivity. The resistor Rp compensates the temperature of the offset voltage by bypassing a part of the current of the bridge piece according to the temperature characteristic of the offset voltage and giving an offset. The resistor RL controls the total amount of current supplied from the constant current source to the bridge to perform temperature compensation of sensitivity.

Since this method does not use a special temperature sensitive element or an active element as an external element, it has an advantage that compensation can be performed with a high degree of accuracy relatively easily, but it has a wide resistance value as an external resistor. You need something in the range. In the case of a general acceleration sensor, the resistance Rp is 300 kΩ to
1.5 MΩ is required, and the resistance RL is 15 kΩ to 10 kΩ
0 kΩ is required.

On the other hand, recently, in response to the demand for miniaturization of the acceleration sensor, an integrated acceleration sensor has been developed in which the strain-sensitive resistance bridge and its output amplification circuit (including temperature compensation and various adjustment circuits) are integrated on the same semiconductor chip. Has been done. In such an integrated acceleration sensor, it is conceivable to form a thin film resistor of a metal thin film on a chip as the temperature compensation resistor described above. However, it is practically difficult to form a resistor on the order of several hundred kΩ with a thin film resistor because it requires a large area. Also, it is not practical to form a thin film resistor having several resistance values on a chip.

[0006]

As described above, in the integrated semiconductor acceleration sensor, if temperature compensation of the offset voltage is performed in the bridge portion, a thin film resistor having a wide range of resistance values is required, There was a problem that it was technically difficult to integrate. The present invention has been made in view of such circumstances, and an object thereof is to provide an integrated semiconductor acceleration sensor capable of compensating the offset voltage temperature characteristic of the entire sensor with a simple configuration. ..

[0007]

According to the present invention, a strain sensitive resistance bridge is formed by combining strain sensitive gauge resistors formed on a semiconductor substrate, and a differential amplifier for amplifying the output of the strain sensitive resistance bridge is also formed on the substrate. In an integrated semiconductor acceleration sensor in which an output amplifier circuit using a type operational amplifier circuit is formed, the differential amplifier circuit is provided with a compensation circuit capable of externally adjusting its offset voltage at the chip stage. It is characterized by

[0008]

The differential type operational amplifier circuit generally has an input offset voltage, and the offset voltage has a temperature drift. Further, when the offset voltage is different, the temperature characteristic of the offset voltage is also different. That is, when the differential type operational amplifier circuit is provided with a compensation circuit capable of adjusting the offset voltage at the chip stage, the temperature characteristic of the offset voltage of the differential type operational amplifier circuit can be arbitrarily generated. Therefore, as in the present invention, if such a compensating circuit is provided in the differential-type operational amplifier circuit for output amplification integrated with the strain-sensitive resistive bridge, the temperature drift of the offset voltage of the differential-type operational amplifier circuit will occur. Is generated so as to cancel the temperature drift of the bridge output, the temperature of the offset voltage is compensated for as a whole sensor. Moreover,
Since the compensation circuit is provided in the differential amplifier circuit that includes active elements, it is necessary to provide thin-film resistors with a wide range of resistance values, such as when performing temperature compensation in the strain-sensitive resistor bridge section without active elements. There is no. That is, by providing the compensation circuit with a thin film resistor that can be adjusted by trimming at the chip stage, temperature compensation can be performed easily and reliably.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an equivalent circuit of a main part of an integrated semiconductor acceleration sensor according to an embodiment of the present invention. x, y,
In the case of a multi-dimensional acceleration sensor in the z direction, such a circuit is provided in each of the x, y and z directions. The strain-sensitive resistance bridge 1 includes strain-sensitive gauge resistors Ra, Rb, Rc.
, Rd is a full-bridge type. In this embodiment, a current source circuit using the operational amplifier circuit OP1 is used as the power supply circuit 2 of the strain-sensitive resistor bridge 1. R1
, R2 are resistors forming a bias circuit of the power supply circuit 2. The strain-sensitive resistor bridge 1 is provided with external resistors Rp and Rr for offset compensation. External resistor RL
Is for adjusting the gain of the power supply circuit 2 together with the resistor R3, whereby sensitivity compensation is performed. In the figure, the low-level side of the strain-sensitive resistor bridge 1 is connected to the connection node of the resistors RL and R3, but this may be the ground potential. The output amplifier circuit 3 of the strain-sensitive resistor bridge 1 includes two differential type operational amplifier circuits OP2 and OP3 each having an input terminal connected to each output terminal of the bridge, and a resistor R for setting these gains.
It is composed of 4, R5 and R6. The strain sensitive resistance bridge 1, the power supply circuit 2, and the output amplifier circuit 3 described above are integrated and formed on a silicon substrate.

2A and 2B are a sectional view and a chip plan view showing an integrated structure of the acceleration sensor circuit. The silicon substrate 11 is the sensor body. As shown in the figure, the silicon substrate 11 has a groove formed therein, a working portion 13 is formed in the center thereof, and a thin flexible portion 12 is formed around the working portion 13, and a strain sensitive gauge resistor 14 is diffused in the flexible portion 12 in a predetermined layout. Has been formed. In FIG. 2 (b), Rx1 to Rx4 are strain sensitive gauge resistors for detecting x-direction acceleration, Ry1 to Ry4 are strain sensitive gauge resistors for detecting y-direction acceleration, and Rz1 to Rz4.
Is a strain sensitive gauge resistor for detecting the z-direction acceleration. A peripheral portion of the silicon substrate 11 is attached to the pedestal 16, and a weight body 15 is attached to the central action portion 13. This sensor main body has a vibration stopper 1 made of glass for limiting the vibration of the action portion 13 above and below the sensor body.
7, 18 are attached and housed in a package 19. Although not shown in the drawing, the peripheral circuit shown in FIG. 1 is integratedly formed on the silicon substrate 11 in addition to the above-described strain sensitive gauge resistor. Bonding pads 21 on the silicon substrate 11 and the package leads 20 are connected by bonding wires 21.

FIG. 3 is a circuit configuration example of the differential type operational amplifier circuits OP2 and OP3 in the output amplifier circuit 3 of FIG.
The basic configuration of the bias circuit 31, the differential circuit main body 32, and the output buffer 33 is known as a general operational amplifier circuit using bipolar transistors. The differential circuit body 32 includes input pnp transistors Q1 and Q2 forming a differential pair, current mirror circuits, that is, npn transistors Q3, Q4 and Q5 forming an active load, and a current source pnp transistor Q6. ing. One input transistor Q of this differential circuit body 32
To the collector of 1 is connected a compensating circuit 34 composed of an npn transistor Q7 and a resistor R13 as shown by a broken line. This compensating circuit 34 is for intentionally generating an offset voltage in the differential circuit by arbitrarily setting the collector current ratio of the two input transistors Q1 and Q2. The resistor R13 is a thin film resistor formed on the integrated circuit chip, and its resistance value can be adjusted by laser trimming.

In the differential circuit main body 32, if the compensation circuit 34 is not provided, the same collector current always flows through the two input transistors Q1 and Q2 due to the active load circuit. The input transistor Q by the compensation circuit 34
By bypassing part of the current on the first side, the collector currents of the two input transistors Q1 and Q2 can be set to different values. Therefore, the resistance R of the compensation circuit 34
The input offset voltage can be easily applied by adjusting 13 by trimming. Since the temperature characteristic of the input offset voltage varies depending on the magnitude of the offset, an appropriate input offset voltage is applied to the output amplifier circuit intentionally so as to cancel the temperature drift of the offset of the strain sensing resistance bridge 1. An offset temperature drift can be provided to compensate for the offset temperature drift of the sensor circuit as a whole.

The above will be described more specifically. Now, assuming that the compensation circuit 34 is not provided, the differential circuit body 3
It is assumed that the collector currents of the transistors Q3 and Q4 forming the active load of 2 are equal to Ic. When the collector current flowing through the compensation circuit 34 is .DELTA.I, the collector current of one input transistor Q1 is Ic + .DELTA.I and the collector current of the other input transistor Q2 is Ic.
If the gains of the input transistors Q1 and Q2 are sufficiently large and the collector current and the emitter current are equal, the base-emitter voltage VBE of these input transistors Q1 and Q2 is
1 and VBE2 are respectively VBE1 = (kT / q) ln {(Ic + ΔI) / Is} VBE2 = (kT / q) ln (Ic / Is). k is the Boltzmann constant, T is the absolute temperature, q is the elementary charge, and Is is the saturation current. Since the input offset voltage VID of the differential circuit body corresponds to the difference between these base-emitter voltages, VID = VBE1−VBE2 = (kT / q) [ln {(Ic + ΔI) / Is} −ln (Ic / Is)]. That is, the input offset voltage VID of the differential circuit
Has a temperature characteristic, and the temperature characteristic can be adjusted by adjusting the current ΔI of the compensation circuit 34.

In actual use, two such operational amplifier circuits are used to construct the output amplifier circuit 3 as shown in FIG. 1, and each operational amplifier circuit has a temperature of the offset voltage as described above. Provide a compensation circuit whose characteristics can be set arbitrarily. As a result, the temperature compensation of the offset can be easily performed in the entire sensor circuit.

The present invention can be applied to the case where an active load is not used as the operational amplifier circuit of the output amplifier circuit. That is, as shown in FIG. 4, in the differential amplifier circuit having the resistance loads R21 and R22, the resistance loads R21 and R22 are formed by thin film resistors that can be adjusted by trimming as in the above-described embodiment. An output amplifier circuit using such a differential amplifier circuit is configured, and the resistance values of these load resistors R21 and R22 are adjusted at the chip stage to compensate for the temperature drift of the strain-sensitive resistor bridge as in the above embodiment. can do. Also in this case, as compared with the case where offset compensation is performed in the bridge portion having no active element, a wide range of resistance is not required, and therefore the same effect as that of the above-described embodiment can be obtained.

[0016]

As described above, according to the present invention, an offset voltage temperature characteristic of the entire sensor can be compensated with a simple structure by providing a compensation circuit in the output amplifier circuit section. The semiconductor acceleration sensor can be obtained.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing a main configuration of an integrated acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of an acceleration sensor of the same embodiment.

FIG. 3 is a diagram showing a configuration of an operational amplifier circuit of an output amplifier circuit section of the embodiment.

FIG. 4 is a diagram showing an operational amplifier circuit in an acceleration sensor according to another embodiment.

FIG. 5 is a diagram for explaining a temperature compensation method for a conventional acceleration sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Distortion resistance bridge, 2 ... Power supply circuit, 3 ... Output amplification circuit, OP1-OP3 ... Differential type operational amplification circuit, 31 ... Bias circuit, 32 ... Differential circuit main body, 33 ... Output buffer,
34 ... Compensation circuit.

Claims (1)

[Claims] 1. A strain sensitive resistor bridge formed by combining a semiconductor substrate, a strain sensitive gauge resistor formed on the substrate, and a differential for amplifying an output of the strain sensitive resistor bridge formed on the substrate. Acceleration sensor having a type operational amplifier circuit, wherein the differential type operational amplifier circuit is provided with a compensation circuit capable of adjusting its offset voltage from the outside at the chip stage. ..