JPH0519796Y2 - - Google Patents

Description

[Detailed description of the invention] Summary of the invention In a pressure sensor that generates an on/off detection output by comparing the output voltage of a pressure-sensitive element with a predetermined reference voltage, the variable range of the reference voltage is set by the pressure-sensitive element. By making it adjustable to match the range of the output voltage, it is possible to obtain homogeneous pressure/output characteristics regardless of variations in circuit elements or other fluctuation factors.

BACKGROUND TECHNICAL FIELD OF THE INVENTION This invention relates to a pressure sensor, more specifically a type of pressure sensor that generates an on or off output depending on applied pressure by discriminating the output of a silicon diaphragm type pressure sensitive element using an appropriate reference voltage. Regarding.

Prior Art The electrical circuit of a conventional pressure sensor is shown in FIG.

In the silicon diaphragm type pressure sensitive element 1, the central part of the back side is etched, and four diffused resistance layers are formed on the surface of the thin diaphragm part formed there, and these are connected to Wheatstone by aluminum wiring and electrodes.・It is assembled into a bridge circuit. This pressure sensitive element 1 is driven by a constant current source 2 through adjusting resistors R and R. The output voltage V ₀ is amplified by an amplifier circuit 3 including an operational amplifier 31.

Generally, the pressure/output voltage characteristics (sensitivity characteristics) of the pressure sensitive element 1 vary widely even when manufactured in the same process, and the output voltage V ₀ widely varies by about +120% from the target value.

Taking into account such variations in the pressure sensitive element 1 and other fluctuation factors, the output voltage V _W of the amplifier circuit 3 is determined by adjusting the amplification factor and the DC bias adjustment circuit so that uniform characteristics can be obtained for all pressure sensors. Sent to 4. This adjustment circuit 4 includes an operational amplifier 41, and the amplification factor is adjusted by an input resistance R _c and a feedback resistance R _f . Trimming resistors R _a and R _b are connected to the non-inverting input terminal of the operational amplifier 41.
A resistance circuit consisting of the following is connected. Resistor R _b is connected between the above non-inverting input terminal and ground _.
are connected between the same input terminal and a constant voltage source (voltage V _b ). These resistances R _a or
The DC bias of the operational amplifier 41 is adjusted by R _b .

The output voltage V _y adjusted by the adjustment circuit 4 is
The signal is sent to one input terminal of a comparator 51 in the comparison output circuit 5. The output voltage of the reference voltage adjustment circuit 6 is connected to the other input terminal of the comparator 51 as the reference voltage.
It is given as V _z .

According to the change in the pressure applied to the pressure sensitive element 1, the output V _x of the comparison output circuit 5 becomes a low (L) level when V _y > V _z , and a high level when V _y < V _z . (H) Level becomes . That is, an on/off output V _x can be obtained depending on the applied pressure.

The reference voltage adjustment circuit 6 has a reference power supply 61 (voltage
It consists of a variable resistor V _R and a resistor R ₁ connected in series with V _a ). The reference voltage V _z output from this circuit 6 can take a value of [R ₁ /(R ₁ +V _R )]V _a ≦V _z ≦V _a by changing the variable resistor V _R . This voltage value V _z can be arbitrarily changed within the above range by the operator depending on the usage conditions.

Therefore, the output voltage V _y of the adjustment circuit 4 is adjusted in advance so that V _yMIN ≒ [R ₁ / (R ₁ + V _R )] V _a V _yMAX = V _a within the applied applied pressure range. must have been done.

Now, the conventional circuit shown in FIG. 1 was adjusted as follows.

Output adjustment of pressure-sensitive element 1 When the applied pressure is 0 kg/cm ² , the resistors R〓 and R〓 are trimmed so that the amplified output voltage V _w of the pressure-sensitive element 1 becomes 0V. In other words, when the output voltage V ₀ of pressure sensitive element 1 deviates in the positive direction, the resistance
R〓 is adjusted and set so that V _w =0.
Conversely, when the output voltage V ₀ is negative, it is trimmed to V _w =0 by adjusting the resistor R〓.

Adjusting the amplification factor in the adjustment circuit 4 Apply the maximum pressure within the applicable range to the pressure sensitive element 1 (at this time, the output V _y takes the minimum value), and
resistor so that the output voltage V _y becomes the target value V _yMIN .
Amplification factor (R _f /R _c ) by trimming R _c or R _f
Adjust. That is, when V _y < V _yMIN ,
Adjust the resistor R _c to reduce the amplification factor and set V _y = V _{y MIN} . When V _y > V _yMIN , the amplification factor is increased by trimming the resistor R _f so that V _y =V _yMIN .

Adjustment of DC Bias in Adjustment Circuit 4 The balance of the operational amplifier 41 is lost by adjusting the resistor R _c or R _f described above. Therefore, resistance
When R _f is trimmed, the resistor R _a is trimmed so that R _f =R _a . Furthermore, when the resistor R _c is trimmed, the resistor R _b is adjusted so that R _c =R _b .

By trimming the resistor R _a or R _b , the value of the bias voltage applied to the non-inverting input terminal of the operational amplifier 41 changes, thereby increasing the output voltage V _y
also changes. Therefore, the value of the power supply voltage V _b is adjusted again so that V _y =V _yMIN .

As described above, adjustment of the electrical circuit of this pressure sensor is extremely complicated, and adjustment of one location greatly affects other locations, making it difficult to make sufficient adjustments. This is because there are many causes of variation. In other words, the causes of variations include variations in the characteristics of the pressure-sensitive element 1, bridges and bridges when applying the reference pressure to the pressure-sensitive element 1.
Level fluctuation due to imbalance, amplifier circuit 3,
DC bias fluctuations caused by variations in resistance in the adjustment circuit 4, etc., and operational amplifiers 31 and 4
1 input offset voltage, current variation, etc.

In addition, in the conventional pressure sensor, there are adjustment resistors R〓, R〓 also in the pressure sensing part near the pressure sensing element 1, and
The other trimming resistor is in the amplification factor and DC bias adjustment circuit 4, and it can be considered that this is included in the amplifier section along with the amplifier circuit 3, so there is also a trimming resistor in the amplifier section, and the IC of the entire circuit
It was difficult to

Overview of the invention Purpose of the invention The purpose of this invention is to provide a pressure sensor that is easy to adjust and in which many parts can be integrated into ICs.

Structure and effect of the invention The pressure sensor according to this invention has a pressure-sensitive element that generates an output voltage according to applied pressure, and two input terminals.One input terminal receives the output voltage of the pressure-sensitive element, and the other input terminal A reference voltage is applied to each terminal, and a comparison circuit generates an on/off detection output according to the comparison result between the output voltage of the pressure-sensitive element and the above-mentioned reference voltage. A reference voltage adjustment circuit is provided that generates the reference voltage that can be adjusted between an upper limit voltage and a lower limit voltage within a range of variation of the output voltage of the pressure sensitive element when applied.

the reference voltage adjustment circuit comprises a first circuit having a first trimming variable resistor and generating the upper limit voltage adjustable by a value of the variable resistor, a second circuit having a second trimming variable resistor and generating the lower limit voltage adjustable by a value of the variable resistor, and a second circuit having an upper limit voltage of the first circuit and a lower limit voltage of the second circuit applied to both ends thereof,
and a variable resistor that outputs the reference voltage that is adjustable between the upper limit voltage and the lower limit voltage.

By applying pressure to the pressure sensitive element, its output voltage varies. the first trimming variable resistor so that the first circuit generates a voltage equal to the upper limit voltage of the variation range of the output voltage of the pressure-sensitive element that occurs when a pressure in an applicable range is applied to the pressure-sensitive element; is adjusted. Further, the second trimming variable resistor is adjusted so that the second circuit generates a voltage equal to the lower limit voltage of the variation range of the output voltage of the pressure sensitive element. In this way, the upper limit of the range of variation in the output voltage of the pressure-sensitive element that occurs when a pressure within the applicable range of the pressure-sensitive element is applied to both ends of the variable resistor for generating the reference voltage included in the reference voltage adjustment circuit. A voltage and a lower limit voltage will be applied.
Thereby, the reference voltage can be adjusted between the upper limit voltage and the lower limit voltage.

The output voltage of the pressure sensitive element and the reference voltage are applied to the comparison circuit, and these output voltages and the reference voltage are compared. The output voltage of the pressure sensitive element varies between the upper limit voltage and the lower limit voltage according to the applied pressure. The reference voltage can also be adjusted between the upper limit voltage and the lower limit voltage. In this way, the reference voltage of the comparator circuit can always correspond to any pressure within the applicable range, regardless of variations in the characteristics of the pressure-sensitive element, offsets of operational amplifiers, etc., and variations in the characteristics of other circuits and elements. can be set to a value of That is, it becomes possible to freely set the threshold pressure level at which the detection output is turned on and off.

As described above, this invention allows all pressure sensors to have exactly the same pressure/output characteristics, regardless of variations in the characteristics of the pressure-sensitive elements and variations in the characteristics of other elements such as the offset of the operational amplifier. , can be obtained only by trimming the trimming variable resistor in the reference voltage adjustment circuit. This trimming can be done easily for the upper limit voltage and the lower limit voltage. Furthermore, since the pressure sensitive section and the amplifier section are not provided with a trimming variable resistor, these circuits can be integrated into ICs, and many parts of the pressure sensor can be integrated into ICs.

Furthermore, according to this invention, as described above, the upper limit voltage and lower limit voltage in the variation range of the output voltage of the pressure sensitive element are generated from the first circuit and the second circuit, respectively, and these voltages are used for generating the reference voltage. Since the voltage is applied to both ends of the variable resistor, the variable range of the output voltage of the pressure-sensitive element always corresponds to the variable range of the resistance value of the variable resistor for generating the reference voltage, regardless of the magnitude of the potential difference between the upper limit voltage and the lower limit voltage. However, the relationship between the adjustment position of the reference voltage generating variable resistor and the sensitivity of the pressure sensor is always constant. Therefore, it is possible to always adjust the sensitivity of the pressure sensor (adjust the reference voltage that defines the boundary between on output and off output) with the same feeling.

Description of examples FIG. 2 shows an embodiment of this invention.

The same circuits and elements as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

In the circuit of FIG. 2, the amplification factor shown in FIG.
A circuit corresponding to the DC bias adjustment circuit 4 is not provided. The amplifier circuit 30 shown in FIG. 2 mainly corresponds to the amplifier circuit 3 shown in FIG. The output voltage V _y of this amplifier circuit 30 is applied to one input terminal of a comparator 51 .

The feature of this invention is that all the trimming resistors are provided in the reference voltage adjustment circuit 60.

The positive output side of the reference power supply 61 (voltage V _a ) is connected to the non-inverting input terminal of the operational amplifier 31 of the above-mentioned amplification circuit 30 via a suitable resistor to provide its bias voltage, and also to the trimming resistor R _K It is connected to the non-inverting input terminal of the operational amplifier 62 of the reference voltage adjustment circuit 60 via the reference voltage adjustment circuit 60 . Another trimming resistor R _L is connected between this non-inverting input terminal and ground. The output voltage of operational amplifier 62 (designated _V1 ) is fed back to its inverting input terminal.

A resistor circuit is connected between the output side of the operational amplifier 62 and ground. This resistance circuit includes a parallel circuit of a trimming resistor _RM and a variable resistor V _R (V _R >> _RM ), and a trimming resistor _RN connected in series to this parallel circuit. Let the voltage at the connection point between this parallel circuit and resistor R _N be V ₂ .
Therefore, a voltage of V ₁ −V ₂ is applied to the variable resistor _VR . The output voltage of the variable resistor V _R is applied to the other input terminal of the comparator 51 as a reference voltage V _Z .

No trimming is performed on the pressure sensitive section including the pressure sensitive element 1 and the amplifier circuit 30. Therefore,
The output voltage V _y of the amplifier circuit 30 will vary over a wide range (about +200%) due to variations in the characteristics of the pressure-sensitive element 1, variations in the DC bias of the amplifier circuit 30, and the like.

By trimming the maximum voltage V ₁ and minimum voltage V ₂ of the variable resistor V _R , the maximum variation range of this output voltage V _y (i.e. V _yMAX ~ V _yMIN ) is brought within the range of these voltages V ₁ ~ _{V 2} Try to fit it in. Since the reference voltage V _z is always within the voltage range V ₁ to _{V 2} , it can always be compared with the output voltage V _y that is within the same range V ₁ to _{V 2} .

Trimming of voltages V ₁ and V ₂ is performed as follows.

Adjustment of Maximum Voltage V ₁ Pressure is applied to the pressure sensitive element 1 and the output voltage of the pressure sensitive element 1, that is, the output voltage V _y of the amplifier circuit 30 is set to its maximum value V _yMAX . Generally, the output V _y is maximized when the minimum pressure within the applicable range is applied. and,
The output voltage V ₁ of the operational amplifier 62 is the maximum voltage above.
Trim resistor R _K or R _L to equal V _yMAX . When the resistor R _K or R _L is trimmed, the output voltage V ₁ of the operational amplifier 62 increases or decreases.
When V _yMAX > V ₁ , resistor R _L is trimmed, and when V _yMAX < V ₁ , resistor R _K is trimmed to reduce V _yMAX.
= _V1 .

Adjusting the minimum voltage V ₂ By changing the pressure applied to the pressure sensitive element 1, the output voltage of the pressure sensitive element 1, that is, the output voltage of the amplifier circuit 30
Let V _y be its minimum value V _yMIN . Generally, when the maximum pressure within the applicable range is applied, the output V _y is minimized. Then, the resistor _RM or _RN is trimmed so that the output voltage V ₂ at the connection point of the resistor circuit consisting of _the resistors RM, V _R , and _RN becomes equal to the minimum voltage V _yMIN . Trimming resistor R _M or R _N increases or decreases the output voltage V ₂ . When V _yMIN > V ₂ , the resistance R _N
When V _yMIN <V ₂ , the resistors _RM are each trimmed so that V _yMIN =V ₂ .

By the above trimming, no matter what pressure within the applicable range is applied to the pressure sensitive element 1, the output voltage _Vy of the amplifier circuit 30 will always fall between _V1 and _V2 . Therefore, the reference voltage _Vz of the comparison output circuit 5 can be set to a value corresponding to any pressure within the applicable range. i.e. the output
The threshold pressure level at which V _x should be turned on and off can be freely set, and the value of the variable resistor V _R can be set after the above trimming to correspond to this pressure.

In the above manner, uniform pressure/output characteristics can be achieved for all pressure sensors by adjusting the reference voltage, regardless of variations in the characteristics of the pressure-sensitive element or characteristics of other elements such as the offset of the operational amplifier. This can be achieved by simply trimming the resistors in the circuit. This trimming is the upper limit voltage
The work is simple as it only needs to be performed for V ₁ and lower limit voltage V ₂ . Furthermore, since trimming resistors are not provided in the pressure sensitive section and the amplification section, it is possible to implement these circuits into ICs, and it is possible to implement many parts of the pressure sensor into ICs.

In the above embodiment, the four resistors R _K , R _L , R _M and R _N were made variable, but in order to adjust the upper limit voltage,
Either one of R _K and R _L may be fixed and only the other variable, and either one of R _M and _RN may be fixed and only the other variable for lower limit voltage adjustment.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an electric circuit of a conventional pressure sensor. FIG. 2 is a circuit diagram showing an embodiment of this invention. 1...Pressure sensitive element, 5...Comparison output circuit, 51...
... Comparator, 62 ... Operational amplifier, V _R ... Variable resistor, R _K , R _L , R _M , R _N ... Trimming resistor.

Claims (1)

[Claims for Utility Model Registration] A pressure-sensitive element that generates an output voltage according to applied pressure, and has two input terminals, one input terminal receives the output voltage of the pressure-sensitive element, and the other input terminal receives the output voltage of the pressure-sensitive element. Each reference voltage is applied, and depending on the comparison result between the output voltage of the pressure-sensitive element and the reference voltage, it is turned on or off.
A comparator circuit that generates an off detection output, and is adjustable between an upper limit voltage and a lower limit voltage in a variation range of the output voltage of the pressure sensitive element when a pressure within the applicable range is applied to the pressure sensitive element. ,
a reference voltage adjustment circuit that generates a reference voltage to be applied to the other input terminal of the comparison circuit; the reference voltage adjustment circuit has a first trimming variable resistor; a first circuit that generates the upper limit voltage; a second circuit that has a second trimming variable resistor and generates the lower limit voltage that can be adjusted by the value of the variable resistor; A pressure sensor comprising a variable resistor to which an upper limit voltage and a lower limit voltage of the second circuit are applied, respectively, and outputs the reference voltage that is adjustable between the upper limit voltage and the lower limit voltage.