JPH05183347A - Signal processing circuit for semiconductor sensor - Google Patents

Abstract

PURPOSE:To compensate an offset of the semiconductor sensor and an offset temperature characteristic altogether. CONSTITUTION:Servo circuits 3a, 3b are connected in parallel with a feedback resistor of operational amplifiers 4a, 4b amplifying an output of the semiconductor sensor. Each of the servo circuits 3a, 3b consist of a kind of an integration circuit in which a capacitor C1(C2) is connected in place of a feedback resistor for the operational amplifier 4a(4b). Thus, it is not required to measure an offset and an offset temperature characteristic of each semiconductor sensor one by one and to compensate the characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor sensor signal processing circuit for calculating and amplifying an output signal of a semiconductor sensor, and more particularly to a signal processing circuit for compensating offset and offset temperature characteristics in a circuit.

[0002]

2. Description of the Related Art In a conventional gauge resistance type semiconductor sensor such as a pressure sensor and an acceleration sensor, in order to compensate for the offset and offset temperature characteristics of the sensor, it is necessary to use FIG.
As shown in, the external compensation resistors RS50 and RP51 are connected to one side or two sides of the bridge of the gauge resistor G in series or in parallel or both. As the external compensation resistors RS50 and RP51, resistors having a temperature coefficient sufficiently smaller than that of the gauge resistor G are used. Further, the connection position and resistance value of this external resistor are selected and calculated corresponding to the characteristics of each sensor.

The output voltages V41, V42 of the sensor are generally offset and offset temperature compensated and then amplified using three operational amplifiers 44, as shown in an example in FIG.

This amplification factor can be adjusted by the feedback resistor R42 as shown in the following formula 1.

[0005]

## EQU1 ## Vout = (1 + 2 × R41 / R42) (V41-V42) + VS VS = VD × R49 / (R48 + R49)

The resistance value of the feedback resistor R42 is adjusted by means such as laser trimming according to the sensitivity characteristic of the sensor chip, whereby the amplification factor is adjusted.

By adjusting the amplification factor, it becomes possible to mass-produce a sensor having a constant sensor sensitivity. The potential setting resistors (R48, R49) adjust the offset voltage of the sensor and the amplifier circuit. By this adjustment, the output signal of the sensor becomes a constant voltage VS with a signal component due to vibration or pressure superimposed.

[0008]

However, the above-described conventional signal processing circuit for semiconductor sensors has the following drawbacks.

(1) Problems with Offset and Offset Temperature Compensation In the conventional compensation method of the signal processing circuit, the semiconductor sensor has one
There was a problem that it was necessary to compensate in a one-to-one correspondence.
That is, since the characteristic of each sensor is measured and the wiring and resistance value of the compensation resistor are calculated corresponding to this characteristic, there is a problem that the measurement time and the calculation time for one semiconductor sensor become long.

(2) Characteristic problem In the conventional signal processing circuit, since the offset characteristic of the semiconductor sensor is compensated on the sensor side, the offset characteristic of the operational amplifier 44 and the offset characteristic of the semiconductor sensor are compensated. There is a problem that the offset voltage that has not been cut off is amplified by the amplifier circuit 44 and the characteristics are deteriorated.

The present invention has been made in view of the above problems, and the offset and offset temperature characteristics can be collectively compensated, and the step of individually measuring the offset characteristics of the sensor and the individual measurement of the offset temperature characteristics of the sensor. It is an object of the present invention to provide a signal processing circuit for a semiconductor sensor that can omit steps.

[0012]

In the semiconductor sensor signal processing circuit according to the present invention, a servo circuit is connected in balance with the feedback resistance of an operational amplifier for amplifying the output of the semiconductor sensor. It is characterized in that a capacitor is connected instead of the feedback resistor of the amplifier.

[0013]

In the conventional signal processing circuit of the semiconductor sensor, the offset characteristic of the semiconductor sensor is compensated on the semiconductor sensor side and the amplification is performed by the operational amplifier. However, in the signal processing circuit for semiconductor sensor of the present invention, The compensation of the offset characteristic of the semiconductor sensor and the amplification of the output voltage are performed only by the servo type amplifier circuit.

Conventionally, the offset voltage and the offset temperature characteristic are compensated in a one-to-one correspondence with the sensor, but in the signal processing circuit for a semiconductor sensor of the present invention,
Since it is not necessary to adjust the circuit according to the characteristics of the sensor, the characteristics can be compensated by the same circuit for the sensor.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment using a semiconductor acceleration sensor as an example of the semiconductor sensor. The semiconductor acceleration sensor of this embodiment is represented as a resistance bridge 1 on the circuit of FIG. The resistance bridge 1 is a Wheatstone bridge circuit including a piezoresistor formed of an impurity diffusion region formed on a thin film portion such as a semiconductor diaphragm or a beam on at least one side. The first and second operational amplifiers 4a, 4b have their non-inverting input terminals connected to the output terminals V2, V1 of the bridge circuit 1, respectively, and their inverting input terminals connected to each other via the first resistor R2. It is connected to the. The first and second operational amplifiers 4a,
Feedback resistors R1 and R6 are connected between the inverting input terminal and the output terminal of 4b, respectively. The inverting and non-inverting input terminals of the third operational amplifier 5 are connected to the output terminals of the first and second operational amplifiers 4a and 4b via the fourth and fifth resistors R10 and R11, respectively. A sixth resistor R12 is connected between the inverting input terminal and the output terminal of the third operational amplifier 5, and its output terminal is connected to the output terminal Vout of this signal processing circuit. The seventh resistor R13 is connected between the non-inverting input terminal and the bias terminal of the third operational amplifier 5. By the first, second and third operational amplifiers 4a, 4b, 5
The amplifier circuit 2 is configured.

The output terminal of the servo circuit 3a as a fourth operational amplifier is connected to the non-inverting input terminal of the first operational amplifier 4a via the eighth resistor R3. A ninth resistor R4 is connected between the non-inverting input terminal of the servo circuit (fourth operational amplifier) 3a and the output terminal of the first operational amplifier 4a. On the other hand, the inverting input terminal of the second operational amplifier 4b is connected to the output end of the servo circuit 3b as a fifth operational amplifier via the tenth resistor R7. The eleventh portion is provided between the non-inverting input terminal of the servo circuit (fifth operational amplifier) 3b and the output terminal of the second operational amplifier 4b.
Resistor R8 is connected. The twelfth and thirteenth resistors R5 and R9 are connected between the inverting input terminals of the servo circuits 3a and 3b and the ground, respectively, and further, the inverting input terminals and the outputs of the servo circuits 3a and 3b. Capacitors C1 and C2 are connected between the terminals and the terminals, respectively. Note that resistors R14 and R15 for potential setting are connected between the power source Vcc and -Vcc.

Next, the operation of the semiconductor sensor signal processing circuit configured as described above will be described. When vibration or acceleration is applied to the semiconductor acceleration sensor, the voltages V1 and V2 at the midpoint of the resistance bridge 1 change in opposite directions. That is, when the voltage V1 rises, the voltage V2 falls,
When the voltage V1 drops, the voltage V2 rises.

The difference (V1-V2) of the output voltage of the acceleration sensor is amplified by the amplification circuit 2 in the subsequent stage. The amplification factor of the amplifier circuit 2 can be adjusted by the feedback resistor R2 as shown in the following mathematical formula 2.

[0020]

## EQU00002 ## Vout = (1 + 2.times.R1 / R2) (R12 / R10) (V1-V2) + VS where R1 = R6, R10 = R11, R12 = R13.

The feedback resistor R2 can be adjusted by laser trimming or the like according to the sensitivity characteristic of the sensor chip.

The servo circuit 3a feeds back the output voltage V3 of the operational amplifier 4a constituting the amplifier circuit 2 to the inverting input terminal of the operational amplifier 4a in the form of integrating the signal component.
The integration time constant is represented by the product of the resistor R5 and the capacitor C1. The output voltage V5 of the servo circuit 3a is the output voltage V3 of the operational amplifier 4a, the resistor R5, and the capacitor C1.
Is expressed by the following Equation 3.

[0023]

[Expression 3] V5 = (1 / C1) ∫ (V3 (t) / R5) × dt = 1 / (C1 · R5) ∫V3 (t) × dt

The potential setting resistors R14 and R15 adjust the operating voltage VS of the amplifier circuit 3. The operating voltage VS is expressed by Equation 4 below.

[0025]

[Formula 4] VS = 2 × Vcc × R15 / (R14 + R15) -Vcc

By this adjustment, the output signal of the semiconductor acceleration sensor becomes a signal obtained by superposing the signal component due to vibration on the constant voltage VS.

Next, a second embodiment of the present invention will be described with reference to FIG.
Will be described.

The semiconductor sensor is represented as a resistance bridge 21 in the circuit of FIG. In order to facilitate the description, a semiconductor acceleration sensor will be assumed and described as an example of the semiconductor sensor.

When vibration or acceleration is applied to the acceleration sensor, the voltage V21 at the middle point of the resistance bridge 21 changes.

The output voltage V21 of the acceleration sensor is amplified by the amplification circuit 22 in the subsequent stage. The amplification factor of the amplifier circuit 22 can be adjusted by the feedback resistor R22 as shown in the following formula 5.

[0031]

(5) Vout = (1 + R21 / R22) V1

The feedback resistor R22 is adjusted by laser trimming or the like according to the sensitivity characteristic of the sensor chip.

The servo circuit 23 feeds back the output voltage of the operational amplifier 24 constituting the amplifier circuit 22 to the inverting input terminal of the operational amplifier 24 in the form of integrating the signal component.
The integration time constant is represented by the product of the resistor R25 and the capacitor C21. The output voltage V22 of the servo circuit 23 is expressed by the following equation 6 using the output voltage Vout of the operational amplifier 24 and the resistor R25 and the capacitor C21. Therefore, this embodiment also has the same effect as the embodiment of FIG.

[0034]

[Equation 6] V22 = (1 / C21) ∫ (Vout (t) / R25) dt = 1 / (C21 · R25) ∫Vout (t) dt

[0035]

Since the semiconductor sensor signal processing circuit according to the present invention can collectively compensate the offset and the offset temperature characteristics, the step of individually measuring the offset characteristics of the sensor and the step of individually measuring the sensor in the manufacturing process of the sensor. The step of measuring the offset temperature characteristic can be omitted. Thereby, labor can be saved and manufacturing costs can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a signal processing circuit for a semiconductor sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a signal processing circuit for a semiconductor sensor according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional semiconductor acceleration sensor.

[Explanation of symbols]

 1, 21, 41; resistance bridge 2, 22; amplifier circuit 3a, 3b, 23; servo circuit 4a, 4b, 5, 24, 44; operational amplifier 42; offset compensation resistor

Claims (1)

[Claims] 1. A servo circuit is connected in balance with a feedback resistance of an operational amplifier for amplifying the output of a semiconductor sensor, and this servo circuit is configured by connecting a capacitor instead of the feedback resistance of the operational amplifier. A signal processing circuit for a semiconductor sensor characterized by the above.