JP2007225515A - Sensor output detection circuit - Google Patents

Abstract

A sensor output detection circuit capable of detecting a shift in input voltage from a sensor and automatically correcting an output signal level to a reference level.
An amplifier 13 for amplifying and outputting an output voltage Vs of a sensor 11, a comparator 14 for comparing an output signal of the amplifier 13 and a threshold Vt, and a threshold for adjusting the threshold Vt. An adjustment unit 15 and an output signal adjustment circuit 18 that adjusts the output signal Vout based on the comparison result of the comparison unit 14 are provided.
[Selection] Figure 1

Description

The present invention relates to a detection circuit that detects an output signal of a pressure sensor or an acceleration sensor.
In a bridge-type pressure sensor or the like, since the sensor element is formed of metal or the like, the balance of the bridge may be lost due to deterioration with time or the like, and the output voltage may deviate from the reference value. Then, since the output signal of the detection circuit that detects and amplifies the sensor output also deviates from the initial reference value, it is necessary to correct the deviation. Therefore, in such a sensor detection circuit, it is necessary to reliably perform the correction process of the output signal.

  FIG. 7 shows a conventional sensor output detection circuit. An output signal of the sensor 1 configured by a bridge circuit is input to the detection circuit 2, and the detection circuit 2 amplifies the output signal of the sensor 1 and outputs an output signal Vout.

  In such a sensor output detection circuit, the sensor 1 may lose the balance of the bridge due to deterioration over time, and the output voltage may deviate from the reference value. When the output voltage of the sensor 1 deviates from the reference value, the output signal of the detection circuit 2 is also deviated. Therefore, it is necessary to manually adjust the output signal level of the detection circuit 2 so as to correct the deviation. .

  In recent years, since the output level of the sensor has become smaller and smaller, it is necessary to set the gain of the detection circuit high. In such a situation, the sensor output shift greatly affects the output signal of the detection circuit.

  In Patent Document 1, the sampling value of the output signal of the temperature sensor and the product of the sampling time are accumulated, the accumulated value is compared with a threshold value set in advance in the memory, and based on the comparison result. A lifetime detector that issues a warning is disclosed.

Patent Document 2 includes a storage unit that holds a no-signal reference value at the time of manufacture and a no-signal reference value at the time of inspection, and can update the output level by updating the no-signal reference value at the time of inspection. A sensor output signal processing circuit is disclosed.
JP 11-273330 A Japanese Patent Laid-Open No. 8-128851

  In the sensor detection circuit shown in FIG. 7, since it is necessary to manually correct the deviation of the output signal, the operation is complicated, and only the output signal deviated from the reference value can be obtained unless appropriate correction processing is performed. There is no problem.

Patent Document 1 does not disclose the idea of performing a correction process based on the comparison result only by issuing a warning based on the comparison result.
Patent Document 2 discloses the idea of updating the reference value at the time of inspection, but does not disclose a configuration for automatically correcting the reference value.

  An object of the present invention is to provide a sensor output detection circuit capable of detecting a shift in input voltage from a sensor and automatically correcting an output signal level to a reference level.

  The object is to amplify and output the output voltage of the sensor, a comparison unit that compares the output signal of the amplification unit and a threshold value, a threshold value adjustment unit that adjusts the threshold value, and This is achieved by a sensor output detection circuit including an output signal adjustment circuit that adjusts the output signal of the amplification unit based on the comparison result of the comparison unit.

  ADVANTAGE OF THE INVENTION According to this invention, the sensor output detection circuit which can detect the shift | offset | difference of the input voltage from a sensor and can correct | amend an output signal level automatically to a reference level can be provided.

(First embodiment)
FIG. 1 shows a principle diagram of the present invention. The output voltage of the bridge-type sensor 11 is input to the detection circuit 12. The detection circuit 12 compares the output signal Vout of the amplification unit 13 with a preset threshold voltage Vt, and amplifies the output voltage Vs of the sensor 11 and outputs the amplified voltage. The comparator 14 is configured to adjust the output signal Vout, and the threshold adjuster 15 is configured to adjust the threshold of the comparator 14 based on the setting signal S from the outside. Moreover, the determination signal Y is output from the comparison part 14 as needed.

  A specific configuration of the detection circuit 12 is shown in FIG. The amplifying unit 13 receives input stage amplifiers 16a and 16b to which the output voltage of the sensor 11 is input, and outputs signals from the input stage amplifiers 16a and 16b, and outputs an output signal Vout obtained by amplifying the difference voltage between the output signals. An output stage amplifier 17 for outputting, and an output signal adjusting circuit 18 for adjusting the voltage level of the output signal Vout of the output stage amplifier 17 are provided.

  The output signal adjustment circuit 18 is connected to one input terminal of the output stage amplifier 17 via a resistor, and the output signal Vout of the output stage amplifier 17 is output based on the adjustment voltage Vc output from the output signal adjustment circuit 18. The output level is adjusted.

  As shown in FIG. 3, in the output signal adjusting circuit 18, for example, eight resistors R1 to R8 are connected in series between the high potential side power source V1 and the low potential side power source V2, and the resistors R1 to R8 are connected to the resistors R1 to R8. Are respectively connected in parallel with switches 19a to 19h.

  The switch circuits 19a to 19h are controlled to open and close based on a 4-bit control signal C1 output from the comparison unit 14. The resistors R1 to R8 are set, for example, such that the resistors R1 and R5 are 2 kΩ, the resistors R2 and R6 are 4 kΩ, the resistors R3 and R7 are 8 kΩ, and the resistors R4 and R8 are 16 kΩ.

  Complementary signals are input to the switch circuits 19a, 19e, 19b, 19f, 19c, 19g, 19d, and 19h, respectively, and when the 19a, 19b, 19c, and 19d are in a conductive state, the 19e, 19f, 19g and 19h are in a non-conductive state. The voltage at the node N1 between the resistors R4 and R5 is output as the adjustment voltage Vc via the amplifier 20.

  With such a configuration, the adjustment voltage Vc output from the amplifier 20 is controlled in 16 stages by controlling the switches 19a to 19h to open and close with the control signal C1. Therefore, the offset voltage of the output stage amplifier 17 can be controlled in 16 steps by the adjustment voltage Vc.

  The threshold adjustment unit 15 includes a threshold setting unit 21 having a memory and a threshold voltage adjustment circuit 22. The threshold value setting unit 21 stores the set value of the threshold voltage Vt from the outside. As shown in FIG. 4, in the threshold voltage adjusting circuit 22, for example, four resistors R11 to R14 are connected in series between a constant current source 23 and a power source Vss, and switches 24a to R14 are connected to the resistors R11 to R14. 24d are connected in parallel. The resistance values of the resistors R11 to R14 are set to 2 kΩ for the resistor R11, 4 kΩ for the resistor R12, 8 kΩ for the resistor R13, and 16 kΩ for the resistor R14.

The potential of the node N2 between the constant current source resistor R11 and the switch 24a is output as the threshold voltage Vt via the amplifier 25.
The switches 24a to 24d are controlled to open and close based on a 4-bit control signal C2 output from the threshold value setting unit 21. Accordingly, the potential of the node N2, that is, the threshold voltage Vt is controlled in 16 steps based on the set value set in the threshold setting unit 21.

  The comparison unit 14 includes a comparison circuit 26, an up / down counter 27, and a control unit 28. The comparator 26 receives the output signal Vout and the threshold voltage Vt. The comparison circuit 26 outputs an H level output signal CR when the output signal Vout becomes higher than the threshold voltage Vt, and outputs an L level output signal CR when the output signal Vout becomes lower than the threshold voltage Vt.

  The up / down counter 27 includes a clock generation circuit and receives an output signal CR of the comparison circuit 26. When the output signal CR of the comparison circuit 26 is maintained at the H level exceeding the period of the clock signal, a count-up operation is performed based on the rising edge of the clock signal, and the output signal CR of the comparison circuit 26 is When the signal is maintained at the L level beyond the period, the countdown operation is performed based on the rising edge of the clock signal.

The period of the clock signal of the up / down counter 27 is set substantially equal to the period of fluctuation of the output voltage Vs of the sensor 11.
The up / down counter 27 outputs an overflow signal OF to the control unit 28 to reset the count value when the count value by the count up operation and the count down operation overflows. In this embodiment, the overflow signal OF1 is output when the count value becomes +4, and the overflow signal OF2 is output to the control unit 28 when the count value becomes -4.

  The control unit 28 changes the control signal C1 output to the output signal adjustment circuit 18 based on the inputs of the overflow signals OF1, OF2. That is, when the overflow signal OF1 is input, the control signal C1 that decreases the adjustment voltage Vc output from the output signal adjustment circuit 18 by one step is output. When the overflow signal OF2 is input, the control signal C1 is output from the output signal adjustment circuit 18. The control signal C1 for raising the adjusted voltage Vc to be increased by one step is output.

  Next, the operation of the detection circuit 12 configured as described above will be described with reference to FIG. In the figure, the input voltage Vs from the sensor 11 is shown as a signal having a constant amplitude and a constant period, and the output signal Vout of the detection circuit 12 is output as a signal obtained by amplifying the input voltage Vs. The output signal Vout is shown ignoring the gain of the detection circuit 12.

  The input voltage Vs is always input as a signal that varies within a range including the reference value Vx, and the output signal Vout is output as a signal that varies within a voltage range including the threshold value Vt corresponding to the reference value Vx. In other words, when the input voltage Vs varies within a range including the reference value Vx, the threshold value Vt is set such that the output signal Vout becomes a signal that varies within a voltage range including the threshold value Vt.

  In this state, the output signal CR of the comparison circuit 26 repeats the H level and the L level at the cycle of fluctuation of the output voltage Vs of the sensor 11. Accordingly, the up / down counter 27 does not perform the count-up operation and the count-down operation, and the overflow signals OF1 and OF2 are not output.

  When the voltage level of the output signal Vs of the sensor 11 decreases and becomes lower than the reference value Vx, and the output signal Vout decreases and becomes lower than the threshold value Vt, the output signal CR of the comparison circuit 26 is maintained at the L level. It becomes. Then, the up / down counter 27 performs a count-down operation. When the count value becomes −4, the overflow signal OF2 is output to the control unit 28 and the count value is reset.

  The control unit 28 switches the control signal C1 by one step based on the overflow signal OF2. Then, the adjustment voltage Vc output from the output signal adjustment circuit 18 is increased by one step.

  Even if the adjustment voltage Vc is increased by one step, if the output signal Vout does not reach the threshold value Vt, the output signal CR of the comparison circuit 26 is maintained at the L level, so the up / down counter 27 repeats the count-down operation. The overflow signal OF2 is output to the control unit 28. Then, the adjustment voltage Vc output from the output signal adjustment circuit 18 is raised again by one step.

  By such an operation, when the adjustment voltage Vc rises to a level including the threshold value Vt, the output signal CR of the comparison circuit 26 is in a state of repeatedly outputting the H level and the L level. Is stopped and the adjustment voltage Vc does not change.

  When the output signal Vout rises and becomes higher than the threshold value Vt, the output signal CR of the comparison circuit 26 is maintained at the H level, so that the up / down counter 27 performs a count-up operation, and the count value is When +4, the overflow signal OF1 is output to the control unit 28.

  When the adjustment voltage Vc output from the output signal adjustment circuit 18 is lowered by one step and the output signal Vout decreases to a level including the threshold value Vt, the overflow signal OF1 is not output and the adjustment voltage Vc does not change.

In the detection circuit 12 as described above, the following operational effects can be obtained.
(1) The shift of the input voltage Vs from the sensor 11 from the reference value Vx is detected, and the level of the output signal Vout is automatically corrected to a range including the reference level, that is, a range including the threshold value Vt. it can.
(2) By changing the operating frequency or overflow value of the up / down counter 27, the speed at which the output signal Vout is adjusted to the range including the threshold value Vt can be arbitrarily set.
(3) If the voltage adjustment step of the output signal adjustment circuit 18 is changed, the speed at which the output signal Vout is adjusted to the range including the threshold value Vt can be changed.
(4) The threshold value Vt can be arbitrarily set from the outside. Therefore, the threshold value Vt according to the characteristics of the sensor 11 can be easily set.
(Second embodiment)
FIG. 6 shows a second embodiment. In this embodiment, a switch 29 is interposed between the comparison circuit 26 and the up / down counter 27 of the first embodiment. The same components as those in the first embodiment will be described with the same reference numerals.

  If the switch 29 is turned on, the operation is the same as in the first embodiment. When the switch 29 is turned off, it functions as a detection circuit that detects the voltage level of the output signal Vout with respect to the threshold value Vt.

  For example, when the sensor 11 is disconnected, the output signal Vout has a voltage level equal to 0V (when the low-potential side power supply voltage of the output stage amplifier 17 is 0V). In such a case, the switch 29 is turned off, and the setting signal S is inputted so that the threshold value Vt becomes 0.5 V which is the lower limit value of the normal output signal Vout.

  Then, the disconnection of the sensor 11 can be detected based on the determination signal Y output from the comparison circuit 26. That is, when the determination signal Y becomes L level, the sensor 11 is disconnected.

In addition, by appropriately setting the threshold value Vt, it can be applied to various detection circuits according to the operation state of the sensor 11 or the type of detection signal.
Further, by inputting a reference value from the outside as the output voltage Vs of the sensor 11, comparing the output signal Vout in that case with a preset threshold value Vt, and outputting a determination signal Y, the input stage amplifier 16a, The total gain of 16b and the output stage amplifier 17 can also be determined.

You may implement the said embodiment in the following aspects.
In the threshold value setting unit 21, a large number of setting values corresponding to various threshold values may be set in advance, and may be appropriately read out and output as the control signal C2.

It is principle explanatory drawing which shows the detection circuit of this invention. It is a circuit diagram showing a first embodiment. It is a circuit diagram which shows an output signal adjustment circuit. It is a circuit diagram which shows a threshold voltage adjustment circuit. It is a wave form diagram which shows operation | movement of the detection circuit of 1st embodiment. It is a circuit diagram which shows 2nd embodiment. It is a circuit diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Sensor 12 Detection circuit 13 Amplification part 14 Comparison part 15 Threshold adjustment part 18 Output signal adjustment circuit 21 Threshold setting part 22 Threshold voltage adjustment circuit 26 Comparison circuit 27 Up / down counter 28 Control part 29 Switch Vs Output voltage Vt threshold Vout output signal

Claims (5)

An amplifier for amplifying and outputting the output voltage of the sensor;
A comparison unit for comparing the output signal of the amplification unit and a threshold value;
A threshold adjustment unit for adjusting the threshold;
An output signal adjustment circuit for adjusting an output signal of the amplification unit based on a comparison result of the comparison unit. The threshold adjuster is
A threshold setting unit for storing a threshold setting value;
The sensor output detection circuit according to claim 1, further comprising a threshold voltage adjustment circuit that generates a threshold value based on the set value. The comparison unit includes:
A comparison circuit for comparing the output signal with a threshold value;
An up / down counter that outputs an overflow signal based on a count-up operation or a count-down operation when the output signal of the comparison circuit is maintained at the H level or the L level for a predetermined time or more;
The sensor output detection circuit according to claim 1, further comprising a control unit that outputs a control signal to the output signal adjustment circuit based on the overflow signal.   4. The sensor output detection circuit according to claim 3, wherein an output signal of the comparison circuit is output as a determination signal.   5. The sensor output detection circuit according to claim 4, wherein a switch is interposed between the comparison circuit and the up / down counter.

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