JPH0351040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor signal processing circuit, and particularly to a sensor signal processing circuit suitable for commonizing circuits and shortening adjustment time.

[Conventional technology]

Conventionally, sensor signal processing circuits have generally been composed of analog arithmetic circuits, an example of which is shown in FIG. FIG. 1 shows a pressure transmitter, which drives the bridge excitation circuit 3 by supplying a power source 1 to the bridge excitation circuit 3 through a transmission line 2,
The resulting bridge (including the sensor)
4 is amplified and converted into a current by a voltage-current conversion circuit 5, and the output, which is this converted current, controls the current flowing through the transmission line 2, and a load resistor connected in series with the power supply 1. A voltage corresponding to the sensor output is generated across the sensor 7. In this method, the transmission line 2 has the functions of power supply and signal transmission, and enables simple transmission. In addition, this arithmetic circuit also compensates for temperature characteristics, nonlinearity, offset, etc.

[Problem to be solved by the invention]

However, since the circuit shown in FIG. 1 is mainly composed of analog arithmetic circuits as described above, it has the following drawbacks.

(1) There are many parts.

(2) Different calculations are performed depending on the type of sensor, so the calculation circuit must be designed individually for each sensor.

(3) There are many adjustment points, and it takes a lot of time to adjust each sensor.

(4) Compensation for temperature characteristics, nonlinearity, offset, etc. is mainly composed of analog calculation circuits, so
Since the compensation characteristics are constrained and fixed, there is a limit to the accuracy improvement.

An object of the present invention is to provide a sensor signal processing circuit that can be configured with a minimum number of components, has high versatility, is easy to adjust, and can improve linearity with high accuracy.

[Means to solve the problem]

In order to achieve the above object, the present invention takes in an analog signal from a main sensor and an analog signal from at least one auxiliary sensor that detects a state quantity including the ambient temperature of this main sensor, and converts each into a digital signal. AD conversion means for detecting an offset amount of the AD conversion means applied to at least the main sensor;
A correction is made to remove the detected offset amount from the digital signal of the main sensor outputted from the conversion means, and the corrected digital signal of the main sensor is converted into the digital signal of the auxiliary sensor outputted from the AD conversion means. The sensor signal processing device is provided with a digital arithmetic device that performs correction based on a signal, and an output means that transmits the signal of the main sensor corrected by the digital arithmetic device to the outside.

Further, another invention of the present invention provides a switch means which inputs an analog signal from the main sensor and a zero reference signal and outputs either one of the signals after switching the output, and a digital signal which takes in the output of the switch means. outputting a command to switch the switch means to the zero reference signal side, and temporarily holding the output signal of the first AD conversion means during the output period of this signal in the holding means. a second AD conversion means that captures an analog signal from an auxiliary sensor that detects a state quantity including the ambient temperature of the main sensor and converts it into a digital signal; subtracting the output signal of the first AD converting means held in the holding means from the output signal of the main sensor, and outputting the subtracted output signal of the main sensor from the second AD converting means. a sensor signal processing device comprising: a digital arithmetic device that corrects the output signal of the auxiliary sensor based on the output signal of the auxiliary sensor; and an output means that transmits the output signal of the main sensor corrected by the digital arithmetic device to the outside; It's what I did.

[Effect]

With this configuration, according to the present invention, the above object of the present invention is achieved through the following actions.

That is, between the output signal of the main sensor and the true measured value (output), there is a state quantity including the ambient temperature of the main sensor (including the ambient temperature of the main sensor and sensor signal processing circuit, power supply voltage, etc.). (hereinafter referred to as environmental state quantities), there is a nonlinearity or error in a certain relationship. Therefore, by measuring these environmental state quantities with an auxiliary sensor and correcting the output signal of the main sensor based on this, true measured values can be obtained with high accuracy. In particular, when the ambient temperature etc. changes,
The nonlinearity of the true measurement value itself changes. In this regard, in the present invention, since the ambient temperature is measured by the auxiliary sensor and the main sensor output is corrected,
Linearity can be improved with high accuracy.

Furthermore, since the above-mentioned correction processing is performed by a digital arithmetic unit, there are no restrictions on compensation characteristics as in an analog arithmetic circuit, and it is possible to perform correction with higher accuracy over a wide range. Also,
By simply setting a correction program such as correction data and coefficients in a digital arithmetic unit, it can be made compatible with various types of sensors, can be configured with a minimum number of parts, has high versatility, and can simplify adjustment work.

Moreover, at least the AD applied to the main sensor is
An offset amount detection means for detecting an offset amount of the conversion means is provided, and a correction is made to remove the detected offset amount from the digital signal of the main sensor output from the AD conversion means. Since errors such as offsets caused by temperature and power supply voltage fluctuations of the converting means can be removed, accuracy is further improved.

Further, according to another invention of the present invention, in the case where the AD conversion means is divided into one for the main sensor and one for the auxiliary sensor, if the switch means is switched to the zero reference side, the offset amount of the AD conversion means, etc. The error is held in the holding means. Then, the offset amount and the like are subtracted and removed from the digital signal of the main sensor by the digital calculation means. Therefore, the correct amount of offset of the AD conversion means can be detected with a simple configuration. Errors such as offsets caused by temperature and power supply voltage fluctuations of the first AD conversion circuit can be removed, further improving accuracy.

Here, the present invention will be explained in more detail. When sensors and analog circuits are provided as products, deterioration over time is usually not a problem due to aging processing, but dependence on temperature or power supply voltage, nonlinearity between input and output signals, etc. can become problems, and Generally speaking, the true measured value (output) and these variables are expressed by a functional relationship as shown in the following equation.

V _put = f (V _io , _Ta , T _c , V _ps ) ...(1) Here, V _io ; Output signal of the sensor, that is, input signal of the sensor signal processing circuit T _s ; Temperature at the sensor point T _c : Temperature at the point of the sensor signal processing circuit V _ps : Power supply voltage of the sensor signal processing circuit Therefore, when aging is finished, the sensor and the signal processing circuit are integrated, and V _put , T _s , T _c ,
Accurately measure the relationship between T _ps and V _io individually, and digitally record the relationship between T ps and V io in ROM (Read
Only Memory) is stored as a coefficient. When using the sensor signal processing circuit, T _c ,
V _ps is sensed internally (on the chip), V _io and T _s are captured by external sensors, and V _put is output by using the coefficients. Note that if the sensor and sensor signal processing circuit are placed in close proximity, T _s
= T _c , and the dimension can be reduced by one.
Furthermore, if an appropriate power supply regulator is used, V _ps =const, and the dimension can be further lowered by one. Calculating the output value itself using the above equation (1) can basically be solved by utilizing the principle of a microprocessor.

On the other hand, in order to make the output value compatible with various sensors and the dynamic range of the measured value, the analog signal flow (wire connection) and gain settings can be freely set, taking into account the number of auxiliary input signals, etc. It is desirable to be able to do this. To this end, the basically necessary preamplifiers, multiplexers, AD conversion circuits, etc. are formed in advance on a Si wafer.
A method of connecting these with final aluminum wiring is considered, and in this way, even when a sensor processor is required for a new sensor,
It can be realized in a relatively short time without designing the entire LSI.

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 2 is an explanatory diagram showing an embodiment of the sensor signal processing circuit according to the present invention. The temperature and pressure of the plant 10 to be controlled are measured by sensor groups 11 and 11, respectively.
The sensor output signal 21 is input to the sensor processor 19 via the sensor 11'. Generally, the signal 21 has a low signal level;
The signals are amplified by preamplifiers 12 and 12' corresponding to each sensor group 11 and 11', respectively. For example, the amplification degree of the preamplifier 12 is
It is determined by the ratio of the input capacitance 13 and the feedback capacitance 13''.The reason why the gain is determined by the capacitance is that the impedance characteristics obtained on the LSI on-chip are This is because the preamplifiers 12 and 12' have better linear characteristics and temperature characteristics.
16', the signal is converted into a digital signal, and is input to the microprocessor 17. The microprocessor 17 receives the digital signal, performs temperature correction and nonlinear correction using the correction coefficients stored in the PROM 22, and inputs the correction results to the output circuit 18. The output circuit 18 is capable of sending out an analog output signal of 4 to 20 mA, and is also capable of outputting a digital signal as it is. This output is the output signal 2 of the sensor processor.
Connected externally as 0.

FIG. 2 shows an example in which the mutual connections of the preamplifiers 12, 12' and the AO converters 16, 16' have been determined for a specific sensor, but as stated earlier, The number of auxiliary inputs, whether a preamplifier is necessary, and the size of the gain will vary depending on the type of sensor and the operating range of the object to be measured. Therefore, it is necessary to completely redesign the sensor/processor at this time, which increases the cost.

Therefore, an embodiment of a sensor signal processing circuit that does not require a complete redesign of the sensor processor will be described with reference to FIGS. 3 and 4. There is a preamplifier 12A on the semiconductor chip surface, and this preamplifier 1
Capacitors 13A to 1 placed near 2A
3D, gain setting operational amplifier 12B, capacitors 13E to 13H placed near this gain setting operational amplifier 12B, multiplexer 2
3. AD converters 16, 16', a macro processor 17, a PROM 22 for setting correction coefficients, and an output drive circuit 18 are incorporated. Connections between the circuits are made by aluminum evaporation or the like between the microprocessor 17, the output drive circuit 18, and the correction coefficient setting PROM 22. Preamplifier 12A, capacitor 13A~13
D, the gain setting operational amplifier 12B, the capacitors 13E to 13H, the multiplexer 23, and the AD converters 16 and 16' are connected in a pre-processing process for final formation as a sensor processor. That is, the final formed micro-
A partial cross-sectional view of the processor is shown in FIG. 4, and several layers are formed on a silicon substrate 50 using processes such as photoetching, diffusion, oxidation, and vapor deposition. Right side P as shown
-NMOS is formed on the well layer 42.
An aluminum electrode 48 is formed on the diffusion layer of the drain 44 and source 44' of this NMOS.
The gate through the oxide film is formed of polysilicon. The left side PMOS has almost the same configuration as the NMOS, so its explanation will be omitted.
A capacitor is formed on the left side of FIG. 4. In this capacitor, a polysilicon layer 47 serving as one electrode is placed on an oxide film formed on an N ⁺ diffusion layer 43, and a dielectric film 51 of _{SiO 2} or nitride is formed on top of the polysilicon layer 47. An aluminum electrode 48 serving as the other electrode is formed thereon. Here, an aluminum electrode is also drawn out from the electrode made of the polysilicon layer 47, so that the structure allows wiring in the final process. Then, on the oxide film with such partial wiring,
A PSG layer 49'' is formed, and final wiring is provided to this PSG layer 49'' using an aluminum layer 48. The aluminum layer 48'' in the PSG layer 49'' is determined depending on the type of sensor, the operating range of the object to be measured, the number of auxiliary inputs, the necessity of a preamplifier, etc. In FIG. This portion is shown as a portion surrounded by a dashed line 41. In addition, in the same figure, the dashed line 40
The area surrounded by 2 indicates a part where the wiring state is the same even if there are differences in the type of sensor, the operating range of the object to be measured, the number of auxiliary inputs, etc.

FIG. 5 shows the connections between the sensor and the sensor processor when a thermocouple is used as the sensor, and the connections inside the sensor processor. Since the output of the thermocouple is at a low level of 10 mV to 100 mV, it is connected to the preamplifier 12. On the other hand, the sensor 11,
Preamplifier 12 and AD converter 16 in the processor
In order to perform temperature correction, a temperature sensor 24 using a band cap voltage or the like is included in the same chip. Further, since the analog circuit in the sensor processor depends on the power supply voltage 15, these chip temperature signals and power supply voltage signals are switched by the multiplexer 24 and converted into digital signals by the second AD converter 16'. In this case, the accuracy of the second AD converter 16' may be lower than that of the first AD converter 16. The wiring connections after the AD converters 16, 16' are the same as in FIG. Note that the connection between the thermocouple, which is the sensor part, and the sensor processor is the sixth one.
As shown in the figure, the thermocouple 63 is connected to the sensor processor 19 via a terminal 60 and a twisted 62/shield 61 wire.

The AD conversion circuit 16 will be shown in detail using FIG. Here, charge-balanced AD conversion is used, and since it is an integral type, it is advantageous against noise on the plant side. The integrator 36 receives a charge proportional to the input signal 21 and a reference pulse charge of the opposite sign that cancels the charge. The output of the integrator 36 is input to the comparator 35, and when it exceeds a certain standard,
The output of the comparator 35 is the reference pulse generation circuit 3
2, thereby controlling the output level of the integrator 36 to be maintained near a constant level. The output of AD conversion is obtained by counting the output of the comparator 35 for a certain period of time, but if this output is left as it is, it will contain errors due to the temperature and power supply voltage dependence of the AD conversion section and preamplifier section. Therefore, the microprocessor 17 corrects the output using the necessary correction value, and the output circuit 1
Send on 8th. Since the correction value is determined depending on the power supply potential 15 and temperature 24 supplied to the chip, this information is taken in by the second AD conversion, and the correction value is selected based on this information. The AD converter 16 has an auto-zero control circuit 30 built-in, and the output from the auto-zero control circuit 30 is connected to an auto-zero switch 37 interposed between the sensor and the operational amplifier 12.
The zero point adjustment of the sensor is performed by outputting the signal to an auto-zero output holding circuit 31 which exchanges signals with the microprocessor 17. That is, auto zero control circuit 3
0, for example, switches the auro-zero changeover switch 37 to the ground potential (zero reference signal) side at regular intervals, and sends a command to the auto-zero output holding circuit 31 to hold the output of the AD conversion circuit 16 at that time. This held output signal has a value corresponding to errors such as offsets caused by fluctuations in temperature and power supply voltage of the amplifier 12 and AD conversion circuit 16. Therefore, microprocessor 1
7, by subtracting the above-mentioned held output signal from the AD conversion output of the sensor 11,
Since errors such as the offset are eliminated, the accuracy of the sensor output can be further improved. In this case, it goes without saying that the process of detecting and correcting the temperatures of the amplifier 12 and AD conversion circuit 16 is unnecessary.

Furthermore, the connection relationship between a pressure sensor using a pressure/resistance conversion element and the sensor/processor 19 is shown using FIG. A current is applied to the bridge circuit by a constant current drive 71 from the sensor/processor 19 side, and the pressure is calculated using a differential voltage corrected by pressure strain. The temperature of the sensor part is related to the voltage drop across the bridge, so
This is assumed to be the first auxiliary input 72. The output of the on-chip temperature sensor 24 is input as the second auxiliary input, and the chip power supply voltage 15 is input as the third auxiliary input via the multiplexer 23. A.D.
The circuit operation after the converter is the same as that shown in FIG. In this case, the correction coefficient value stored in the PROM collectively accounts for sensor temperature dependence, nonlinearity, on-chip temperature sensor error, temperature dependence, power supply dependence, nonlinearity, etc. of the preamplifier and two AD converters. It is stored so that it can be corrected. Therefore, there is no need for the wasteful work of correcting each part each time.

In the above embodiment, a microprocessor is used to perform the correction calculation, but it is not necessary to be limited to the microprocessor; for example, the DDA adder can be operated by timing directly with the output of the comparator. Of course, it is also possible to do so.

Furthermore, although the above-mentioned embodiment shows an example in which the basic circuit is arranged on the same chip, the essence of the invention will not be impaired in any way even if this configuration is divided into multiple chips. Needless to say.

〔Effect of the invention〕

As is clear from the above, the sensor signal processing circuit according to the present invention can be configured with a minimum number of components, has high versatility, is easy to adjust, and has highly accurate linearity. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a conventional sensor signal processing circuit, FIG. 2 is a circuit diagram showing an embodiment of a sensor signal processing circuit according to the present invention, and FIG. 3 is a circuit diagram showing an embodiment of a sensor signal processing circuit according to the present invention. 4 is a circuit diagram showing another embodiment of the sensor signal processing circuit according to the present invention; FIG. 4 is a configuration diagram when the circuit shown in FIG. 3 is incorporated on a semiconductor chip; FIG. 5 is a circuit diagram showing another embodiment of the sensor signal processing circuit according to the present invention The circuit diagrams and FIGS. 6 to 8 are circuit diagrams showing other embodiments of the sensor signal processing circuit according to the present invention. 10...Plant, 11,11'...Sensor, 12...
Operational amplifier, 16...AD converter, 17...Microprocessor, 18...Output drive circuit, 19...Sensor signal processing circuit, 22...PROM.

Claims (1)

[Claims] 1. In a sensor signal processing device that processes an analog signal from a main sensor, an analog signal from at least one auxiliary sensor that detects an analog signal from the main sensor and a state quantity including the ambient temperature of the main sensor. AD conversion means for taking in signals and converting them into digital signals, offset amount detection means for detecting an offset amount of the AD conversion means applied to at least the main sensor, and offset amount detection means for detecting the offset amount of the AD conversion means applied to at least the main sensor; a digital calculation device that performs correction to remove the detected offset amount from the digital signal, and corrects the corrected digital signal of the main sensor based on the digital signal of the auxiliary sensor output from the AD conversion means; and output means for transmitting the signal of the main sensor corrected by the digital arithmetic device to the outside. 2. The sensor signal processing device according to claim 1, wherein the auxiliary sensor includes an auxiliary sensor that detects a power supply voltage of the sensor signal processing device. 3. The sensor signal processing device according to claim 1, wherein the auxiliary sensor includes an auxiliary sensor that detects an ambient temperature of the sensor signal processing device. 4. The sensor signal processing device according to claim 1, wherein the AD conversion means switches and takes in the output signal of the auxiliary sensor via a multiplexer. 5. In the sensor signal processing device according to claim 1, the AD conversion means includes a first AD conversion means that receives the output signal of the main sensor, and a first AD conversion means that receives the output signal of the auxiliary sensor via a multiplexer. A sensor signal processing device comprising: a second AD conversion means for switching and inputting. 6. The sensor signal processing device according to claim 1, wherein the AD conversion means, the digital calculation device, and the output means are formed on the same semiconductor chip surface. Device. 7 In a sensor signal processing device that processes an analog signal from the main sensor, a switch means receives the analog signal from the main sensor and a zero reference signal as input, and switches and outputs one of the signals; and an output of the switch means. a first AD conversion means that takes in and converts it into a digital signal, outputs a command to switch the switch means to the zero reference signal side, and outputs an output signal of the first AD conversion means during an output period of this signal. a control means for temporarily holding the holding means; a second AD conversion means for capturing an analog signal from an auxiliary sensor that detects a state quantity including the ambient temperature of the main sensor and converting it into a digital signal; and the first AD. The output signal of the first AD conversion means held in the holding means is subtracted from the output signal of the main sensor outputted from the conversion means, and the subtracted output signal of the main sensor is converted to the second output signal of the main sensor. A digital calculation device that performs correction based on the output signal of the auxiliary sensor output from the AD conversion device; and an output device that transmits the output signal of the main sensor corrected by the digital calculation device to the outside. Sensor signal processing device.