JPH09210831A - Sensor module and its characteristic adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor module which is simple and whose characteristic can be adjusted with high accuracy and to provide its characteristic adjusting method. SOLUTION: A sensor module 1 is constituted in such a way that an absolute pressure-type pressure sensor body 3, an operational amplifier IC 4 and a digital potentiometer 5 which is used as a variable resistance for sensor-characteristic adjustment are mounted on a circuit board 2 and that a sensor output terminal OUT and a terminal ADJ for characteristic adjustment are installed. The sensor module 1 is operated in a state that it is housed in an airtight container whose atmosphere can be adjusted and that signal lines which are connected to the sensor output terminal OUT and to the terminal ADJ for characteristic adjustment are derived to the outside of the airtight container. While the output of the sensor module 1 is being measured, the adjusting signal of the digital potentiometer 5 is transmitted to the terminal ADJ for characteristic adjustment via the signal line from the outside of the airtight container, and a sensor characteristic is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor module having a sensor body and its peripheral circuit parts mounted thereon, and more particularly to a characteristic adjusting method useful when applied to a sensor module for measuring absolute pressure.

[0002]

2. Description of the Related Art A semiconductor pressure sensor is obtained by packaging a sensor chip having a pressure sensitive resistor. Usually, a semiconductor pressure sensor needs adjustment for improving characteristic variations such as offset voltage and sensitivity and temperature characteristics.
In order to adjust this characteristic, the sensor circuit is constructed by combining the pressure sensor body with peripheral circuits such as an output amplifier circuit and a temperature compensation circuit, and the output characteristic is measured to adjust the resistance in the circuit. Be seen. As the resistor for adjusting the characteristic, a semi-fixed resistor for mechanical adjustment, a thin film resistor or a thick film resistor for adjustment by laser trimming or the like is used. In the case of an integrated pressure sensor in which a part of the peripheral circuit is formed on the sensor chip, there is also a method of forming a thin film resistor for adjustment on the sensor chip and performing adjustment before packaging.

Of the semiconductor pressure sensors, in the case of an absolute pressure type pressure sensor, the sensor chip is finally vacuum-sealed. Therefore, even if trimming adjustment is performed in the atmosphere before packaging, after vacuum-sealing. In the finished product, the deviation of characteristics cannot be avoided. For this reason, normally, a sensor module that includes a packaged sensor body and a peripheral circuit that includes an adjustment resistor is configured, and this module is housed in an airtight sealed container that can be adjusted in temperature and pressure. Output characteristics are checked. That is, first, the output characteristic is measured, the adjustment value of the resistance value is calculated based on the measured value, the sensor module is taken out from the closed container, and the resistance value is adjusted.

[0004]

The characteristic adjusting method of the conventional absolute pressure type pressure sensor described above has the following problems. First, since the adjustment amount of the resistance is based on the prediction by calculation, an adjustment error is inevitably generated, and it is difficult to perform highly accurate adjustment. Secondly, since the sensor module is placed in a closed container for measurement, the resistance value cannot be adjusted at the same time while performing the measurement, and the adjustment work requires time and effort. If the measurement and adjustment work is repeated multiple times, productivity will be significantly impaired. Third, in the case of adjustment by trimming the thick film resistance or the thin film resistance, it is usually not possible to perform readjustment of adjusting the high resistance side to the low resistance side. In the case of a semi-fixed resistor, adjustment can be performed multiple times, but this is also limited to several times from the viewpoint of reliability.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sensor module and a method for adjusting the characteristics thereof, which enables easy and highly accurate adjustment of the characteristics.

[0006]

A sensor module according to the present invention includes a circuit board, a sensor body mounted on the circuit board, and an output processing circuit mounted on the circuit board for processing an output of the sensor body. And a part of the output processing circuit is constituted by a digital potentiometer used as a variable resistor for adjusting the characteristics of the sensor output, and a resistance value for the sensor output terminal for extracting the output of the output processing circuit and the digital potentiometer. It is characterized in that it has a characteristic adjustment terminal for introducing a variable adjustment signal.

In the sensor module characteristic adjusting method according to the present invention, in the sensor module described above, a signal line connected to the sensor output terminal and the characteristic adjusting terminal is led out of the specific environment under a specific environment. And adjusting the sensor characteristic by transmitting an adjustment signal of the digital potentiometer from the outside of the specific environment to the characteristic adjusting terminal via the signal line while measuring the output of the sensor module. It has a feature.

In the sensor module characteristic adjusting method according to the present invention, a pressure sensor main body and an output processing circuit for processing the output of the pressure sensor main body are mounted on a circuit board, and a part of the output processing circuit is provided. Is composed of a digital potentiometer used as a variable resistor for adjusting the characteristic of the sensor output, and for adjusting the characteristic for introducing an adjustment signal for varying the resistance value to the sensor output terminal for taking out the output of the output processing circuit and the digital potentiometer. A pressure sensor module is configured by providing a terminal, and the pressure sensor module is housed in a closed space in which temperature and pressure can be adjusted, and a signal line connected to the sensor output terminal and the characteristic adjusting terminal is connected to the closed space. Operate in a state where it is led to the outside, and change the temperature and pressure of the closed space to While measuring the output of the sensor module, it is characterized in that the adjustment of the sensor characteristics by sending an adjustment signal of the digital potentiometer from outside of the sealed space to the characteristic adjustment terminal through the signal line.

According to the present invention, a sensor module is constructed by using a digital potentiometer as an output adjusting element instead of a conventional thin film resistor or semi-fixed resistor, and the sensor module is operated in a specific environment such as a closed container. The sensor characteristics are adjusted by sending an adjustment signal from the outside through a signal line while checking the output characteristics. Therefore, unlike the conventional case, the environmental conditions of the process of measuring the sensor characteristics and the environmental conditions of the process of adjusting the sensor characteristics do not change, and in particular, highly accurate characteristic adjustment of the absolute pressure type pressure sensor or the like becomes possible. Also, by using the digital potentiometer, it is possible to make adjustments multiple times, and it is easy to repeat the work of measuring the sensor output characteristics and the work of adjusting the characteristics, improving workability and making adjustments even more precise. It is possible to obtain high yield. Further, since the output measurement and the characteristic adjustment can be continuously performed under the same environmental condition, the adjustment work can be easily automated and the cost of the sensor module can be reduced.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an absolute pressure type pressure sensor module 1 according to an embodiment of the present invention. The pressure sensor module 1 includes an operational circuit IC 2 formed by integrating a pressure sensor main body 3 and a plurality of operational amplifiers for forming an output processing circuit on an electronic circuit board 2, and a sensor characteristic which is a part of the output processing circuit. The digital potentiometer 5 used as a variable resistance for adjustment is mounted and configured. The digital potentiometer 5 is, for example, a variable resistance device that controls 256 positions of 4 channels by digital data.

Although not shown in detail in FIG. 1, wiring is preliminarily formed on the circuit board 2, and a resistor and the like are mounted in addition to the sensor main body 3, the operational amplifier IC 4 and the digital potentiometer 5 to form a sensor circuit. Composed. Although a specific configuration of the sensor circuit will be described later, a lead terminal 6 provided on one side of the circuit board 2 has a sensor output terminal OUT and a characteristic adjusting terminal which is a terminal for adjusting resistance component data stored in the digital potentiometer 5. ADJ, voltage application terminals V1 and V2, ground terminal GND and the like are assigned.

The absolute pressure type pressure sensor main body 3 is constructed, for example, as shown in FIG. The sensor chip 21 on which the pressure-sensitive resistor is formed is mounted on a metal base 22, and each terminal of the sensor chip 21 is a lead 23 provided on the base 22.
To a wire 24. A hole communicating with the rear surface of the diaphragm of the sensor chip 21 is formed in the center of the base 22, and a pressure guiding pipe 25 is connected to the hole. The whole is vacuum-sealed by a cap 26, and the upper space of the sensor chip 21 serves as a vacuum reference pressure chamber.

FIG. 3 is an equivalent circuit of the digital potentiometer 5. The adjustment signal input to the adjustment terminal ADJ is a serial signal. As shown in FIG. 4, the first two bits are the address AD for variable resistance selection, and the following eight bits are data DA for determining the resistance value. . The adjustment signal is converted into parallel data by the serial / parallel conversion circuit 31, and the leading 2-bit address AD is supplied to the selector 32, which is followed by the latch circuits 33a to 33d selected by the selector 32. The bit data DA is latched. The latched data determines the division value of each resistance circuit 34a-34d, and the variable resistances VR1-VR4 are adjusted by this. In this example, four variable resistors VR1 to VR are provided by one serial adjustment signal.
4 can be adjusted, only one characteristic adjustment terminal ADJ of the pressure sensor module 1 is required, and it is possible to avoid an increase in the number of terminals beyond necessity and an increase in the size of the module 1.

FIG. 5 is an equivalent circuit of the sensor module 1. Ra, Rb, Rc, and Rd are pressure-sensitive resistors of the sensor main body 3, and these constitute a full-bridge type bridge circuit 51 which is the sensor circuit main body. A constant current type bridge drive circuit 52 is formed by one operational amplifier OP1 and resistors R1 to R3 in the operational amplifier IC4, and the other three operational amplifiers OP2, OP3, OP4 and resistors R4 to R4.
The output amplifier circuit 53 is configured by R9.

The output side terminals of the two pressure-sensitive resistors Rc and Rd forming the bridge circuit 51 are led out from the sensor body 3 without being directly connected, and the potentiometer variable shown in FIG. 3 is provided between these terminals. The resistor VR1 is inserted. The variable resistor VR1 is used as a resistor for adjusting the offset voltage while maintaining a bridge balance. Further, the variable resistor VR2 of the potentiometer shown in FIG. 3 is inserted in the output amplifier circuit 53 as a resistor for adjusting the amplification factor. In the figure, the case where the two variable resistors VR1 and VR2 of the digital potentiometer 5 are used for offset adjustment and output amplification factor adjustment is representatively shown, but only one of them may be used, or further variable. The resistors VR3 and VR4 can be used, for example, for adjusting the current of the drive circuit 52 and for adjusting other characteristics.

FIG. 6 shows a system for measuring and adjusting sensor output characteristics using the pressure sensor module 1 as described above. The closed container 61 includes a plurality of sockets 62 (6
2a to 62c) each having a sensor module 1
By attaching (1a to 1c), the pressure and temperature of the internal atmosphere can be arbitrarily set. And FIG.
Characteristic adjustment terminal ADJ and sensor output terminal OU shown in
A plurality of signal lines 63 connected to T and other terminals are led out of the closed container 61.

Outside the closed container 61, a digital multimeter 64 for measuring the output voltage of the sensor module 1,
A computer 65, which calculates the adjustment amount of each variable resistance by taking in the measurement value of the digital multimeter 64 and performing a comparison calculation with the adjustment target value, and other devices (for example, a power supply device) are arranged. In the computer 65, the calculated adjustment amount is converted into an adjustment signal by a preinstalled program and an operator's operation, and this is converted via the signal line 63 into the digital potentiometer 5 of the sensor module 1, that is, the characteristic adjustment terminal ADJ of FIG. And the variable resistors VR1 and VR2 are adjusted accordingly. The output of the sensor module 1 does not need to be measured by the digital multimeter 64,
It can also be loaded into the computer 65 via an A / D converter.

With such a system configuration, the output characteristic of the pressure sensor module 1 is adjusted as follows. First, the pressure, temperature, etc. in the closed container 61 are controlled to set a specific environment for the pressure sensor module 1. The output voltage of the pressure sensor module 1 is measured under this specific environment, and the measured value is loaded into the computer 65. The measured value and the adjustment target value that have been captured are compared and calculated to calculate the adjustment amount. The calculated adjustment amount is converted into an adjustment signal and sent to the pressure sensor module 1 via the signal line 63, and the variable resistance VR1,
Adjust VR2. The output voltage of the adjusted pressure sensor module 1 is measured again, and it is confirmed whether or not the output voltage is the adjustment target value. If the confirmed output voltage does not reach the adjustment target value, perform the adjustment again, and repeat the measurement and adjustment until the output voltage reaches the adjustment target value. The above measurement and adjustment are repeated under other necessary atmospheric conditions.

As described above, according to this embodiment, since the pressure sensor module is constructed by using the digital potentiometer as the variable resistance, all the adjustment of the pressure sensor module can be performed through the signal line. That is,
Adjustment work can be performed while setting the pressure sensor module in a closed container under specific environmental conditions and measuring the output voltage. Further, by using the potentiometer as the variable resistance for adjustment, the measurement and the adjustment can be repeated without putting the sensor module in and out of the closed container, and the adjustment can be performed with high accuracy. Specifically, in the case of the conventional trimming method using a thin film resistor or the adjustment method using a semi-fixed resistor, the variation of the full-scale output voltage is about ± 5%, whereas this embodiment suppresses the variation to about ± 2%. I was able to. Further, in the case of the conventional method, the yield was 85 to 95%, but according to this embodiment, the yield of almost 100% can be obtained. Also, since the output voltage measurement and adjustment can be repeated using the same device while the sensor module is housed in a closed container, the adjustment process can be automated, reducing man-hours and workers, and reducing costs. become.

In the embodiment, the pressure sensor module for absolute pressure measurement has been described. However, the present invention is not limited to this, and the output changes due to the packaging, and therefore the precision before adjustment is improved. Similar to other sensor modules that are difficult to adjust, sensor modules that require adjustment in a special atmosphere such as gas sensors, and various sensor modules that require adjustment by changing the external environment. This invention can be applied to.

[0021]

As described above, according to the present invention, a sensor module is constructed by using a digital potentiometer as a characteristic adjusting element, and the sensor module is operated in a specific environment such as an airtight container to obtain a sensor output. While checking the above, by sending an adjustment signal from the outside through the signal line to adjust the characteristics, it is possible to adjust the characteristics with high precision such as an absolute pressure type pressure sensor. Also, by using a digital potentiometer, it is possible to make adjustments multiple times, and it is easy to repeat the work of measuring the sensor output and adjusting the characteristics, improving workability and making adjustments even more precise. Therefore, it is possible to reduce the cost of the sensor module by high yield and automation.

[Brief description of drawings]

FIG. 1 shows a pressure sensor module according to an embodiment of the present invention.

FIG. 2 shows a configuration of an absolute pressure type pressure sensor main body in the embodiment.

FIG. 3 shows a configuration of a digital potentiometer according to the same embodiment.

FIG. 4 shows an adjustment signal of the digital potentiometer.

FIG. 5 shows an equivalent circuit of the pressure sensor module in the embodiment.

FIG. 6 shows a configuration of a measurement / adjustment system of the same embodiment.

[Explanation of symbols]

1 ... Pressure sensor module, 2 ... Electronic circuit board, 3 ... Pressure sensor main body, 4 ... Operation amplifier IC, 5 ... Digital potentiometer, 6 ... Lead terminals, VR1, VR2 ... Variable resistance (digital potentiometer), ADJ ... Characteristic adjustment Terminal, OUT ... Sensor output terminal, 61 ... Airtight container, 62 ... Socket, 63 ... Signal line, 64 ... Digital multimeter, 65 ... Computer.

Claims (3)

[Claims] 1. A circuit board, a sensor body mounted on the circuit board, and an output processing circuit mounted on the circuit board for processing an output of the sensor body, wherein a part of the output processing circuit is provided. It is composed of a digital potentiometer used as a variable resistor for adjusting the characteristic of the sensor output, and a sensor output terminal for extracting the output of the output processing circuit and a characteristic adjusting terminal for introducing an adjusting signal for varying the resistance value to the digital potentiometer. A sensor module comprising: 2. The sensor module according to claim 1, wherein the sensor module is operated under a specific environment with a signal line connected to the sensor output terminal and the characteristic adjusting terminal being led out of the specific environment. The characteristics of the sensor module are characterized in that the sensor characteristics are adjusted by transmitting an adjustment signal of the digital potentiometer from the outside of the specific environment to the characteristic adjustment terminal through the signal line while measuring the output of Adjustment method. 3. A pressure sensor body and an output processing circuit for processing the output of the pressure sensor body are mounted on a circuit board,
In addition, a part of the output processing circuit is configured by a digital potentiometer used as a variable resistor for adjusting the characteristic of the sensor output, and a sensor output terminal for extracting the output of the output processing circuit and the digital potentiometer for varying the resistance value. A pressure sensor module is configured by providing a characteristic adjustment terminal for introducing an adjustment signal, and the pressure sensor module is housed in a closed space in which temperature and pressure can be adjusted and connected to the sensor output terminal and the characteristic adjustment terminal. A signal line to the outside of the closed space, the temperature and pressure of the closed space is changed to measure the output of the pressure sensor module, and the signal line from the outside of the closed space is passed through the signal line. To send the adjustment signal of the digital potentiometer to the characteristic adjustment terminal. A method for adjusting the characteristics of a pressure sensor module, which comprises adjusting the sensor characteristics.